This PDF file contains the front matter associated with SPIE Proceedings Volume 10363, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Since the first report on the solid-state perovskite solar cell with power conversion efficiency (PCE) of 9.7% in 2012 by our group, its certified PCE now reaches 22%. It is believed that perovskite solar cell is promising next-generation photovoltaics (PVs) due to superb performance and very low cost. In this talk, the history of perovskite photovoltaics will be briefly presented along with their scientific progress. Methodologies to achieve hysteresis-free, stable and high PCE perovskite solar cells will be introduced. Lewis acid-base adduct approach has been found to be very reliable and reproducible method to get high quality perovskite layer minimizing non-radiative recombination. Non-stoichiometric precursor in adduct process demonstrated grain boundary healing effect, which further improved voltage and fill factor due to long carrier life time of perovskite and improved charge transporting at grain boundary as well. Grain boundary healing process yields PCE as high as 20.4%. Moisture was effectively protected and hysteresis was significantly reduced by introducing 2-dimensioanl perovskite at grain boundary of 3-dimensional perovskite grains. Ion migration is one of factors affecting stability and hysteresis, which can be deactivated by 2-dimensional perovskite with higher barrier energy for ion migration. Thermal stability of perovskite material was found to be stable up to 120°C in the absence of moisture, but that of full device was sensitive to selective contacts, indicating that thermally stable selective contacts are equally important. Universal method to remove hysteresis will be also given in this talk.

The phase separation between donor and acceptor molecules within the active layer of an organic solar cells dictates the morphology and hence is key to the recombination rate and ultimately the performance of the organic solar cell. Molecular dynamics (MD) simulation is a suitable technique to understand this phenomenon; however, conventional all-atom MD simulations cannot reach the appropriate length and time scales to compare with macroscopic observation. Even with the many available coarse-grained MD models, it is difficult to reach these scales. Therefore, we introduce here a 2D compact model to overcome this challenge, built by multiscale coarse-graining. First, we simulate systems including conjugated polymers, fullerenes, and organic solvents using all-atom MD to extract information about molecular conformation and packing. This includes an analysis of polymer solution behavior, fullerene clustering, and binary and tertiary mixing properties. These results are then used to systematically parameterize the molecules used in 2D coarse-grained MD simulations. The 2D simulations probe experimentally relevant length scales that were previously intractable to sample by other MD simulation methods. Using this model, we explore ternary systems including polymer, fullerene, and solvent molecules to investigate the phase separation process between polymer donors and fullerene acceptors. In this scheme, we additionally introduce explicit solvent evaporation to emulate realistic processing conditions. We quantify phase separation domain sizes that are comparable to experimentally observed values from resonant soft x-ray scattering. In addition, we extend this framework to other chemical species to demonstrate the flexibility of the approach.

Polymer Solar Cells (PSCs) continue to be a promising third generation, low energy-budget, lead-free PV technology. Efficiencies have now improved to over 12% and a new class of materials (small molecule acceptors) have recently provided rapid improvements that promise further advances. Significant effort in the field is being spent on synthetic efforts to tune the electronic structure and in understanding charge generation. In contrast, we explore the correlation of fill factor to the purity of domains as measured with soft x-ray scattering, and how said purity is controlled by thermodynamically metastable morphologies. We will argue that ideal materials systems will have a Flory Huggins interaction parameter χ that naturally leads to mixed domains that have a composition close the fullerene/SMA percolation threshold. Systems that are too miscible will have excessive bimolecular recombination. Systems too immiscible need to be quenched for best performance, are thus unstable and eventually produce fullerene islands that trap charges. Although some of these concepts are known and are indirectly referred to as “miscibility”, quantitative relations remained largely elusive. Understanding molecular interactions is even more important for conventional ternaries devices. In some cases, the two donor polymer used can have unfavorable thermodynamic interactions (χ = - 0.56 at 296 °C) that prevent improved performance due to lack of phase separation and alloying of the two donors. Overall, we advocate a program to measure χ(T) in model systems in order to develop a frame-work that will eventually lead to computational approaches that allow predictions of χ as a function of molecular tuning before synthesis of a targeted compound is attempted.

Singlet exciton fission is a process where an excited singlet state splits into two triplets, thus leading to generation of multiple excitons per absorbed photon in organic semiconductors. Herein, we report a detailed exciton management approach for multiexciton harvesting over a broadband region of the solar spectrum in singlet fission sensitized organic photodiodes. Through systematic studies on the model cascade of pentacene/rubrene/C₆₀, we found that efficient photocurrent generation from pentacene can still occur despite the presence of a >10nm thick interlayer of rubrene in between the pentacene/C₆₀ heterojunction. Our results show that thin rubrene interlayers of thickness < 5 nm are effective in maintaining the delicate balance between two free charge generation channels that progress independently via the electron and hole transfer routes. The contribution to photocurrent from pentacene despite having a reasonably thick rubrene interlayer, that too with higher triplet energy (T1=1.12 eV) than pentacene (T1= 0.86 eV), makes its operation a rather interesting result. We discuss the role of rubrene interlayer film discontinuity, triplet exciton reflection from rubrene interlayer and triplet energy transfer from rubrene to pentacene layer followed by diffusion of triplet excitons through rubrene as plausible mechanisms that would enable triplet excitons from pentacene to generate significant photocurrent in a multilayer organic heterojunction.

How photoexcitations evolve in time into Coulomb-bound electron and hole pairs, called excitons, and unbound charge carriers is a key cross-cutting issue in photovoltaic and optoelectronic technologies. Until now, the initial quantum dynamics following photoexcitation remains elusive in the organometal halide perovskite system. Here we reveal excitonic Rydberg states with distinct formation pathways by observing the multiple resonant internal quantum transitions using ultrafast terahertz quasi-particle transport. Nonequilibrium emergent states evolve with a complex co-existence of excitons, unbound carriers and phonons, where a delayed buildup of excitons under on- and off-resonant pumping conditions allows us to distinguish between the loss of electronic coherence and hot state cooling processes. The terahertz transport with rather long dephasing time and scattering processes due to discrete terahertz phonons in perovskites are distinct from conventional photovoltaic materials. In addition to providing implications for ultrafast coherent transport, these results break ground for a perovskite-based device paradigm for terahertz and coherent optoelectronics.

Hybrid metal halide perovskites (stoichiometry AMX3) have recently emerged as low-cost active materials in PV cells with power conversion efficiencies in excess of 21%. We discuss how parameters essential for photovoltaic operation, such as crystallinity, photostability, charge carrier mobility and diffusion lengths are altered with substitutions of the organic A cation (e.g. methylammonium versus formamidinium), the metal M cation (e.g. Pb2+ or Sn2+) and the halide X anion (I- versus Br-). We focus on two 3D perovskite systems that have attracted interest lately, lead-free ASnI3 (optical bandgap ~1.3 eV) and the mixed organic lead iodide/bromide system APb(BryI1-y)3 whose band gap can be tailored between ~1.5 eV (FAPbI3) and ~2.3 eV (FAPbBr3). We show that unintentional hole doping in tin iodide perovskites introduces fast recombination pathways that can be moderated by crystal structure [1] and introduces a radiative quasi-monomolecular charge recombination channel [2]. In addition, we demonstrate that charge-carrier diffusion and recombination in FA1-xCsxPb(BryI1-y)3 depends on a complex interplay between changes in morphology and electronic bandstructure with bromide fraction y [3,4,5]. References [1] Parrott, Milot, Stergiopoulos, Snaith, Johnston, Herz, J. Phys. Chem. Lett. 7, 1321 (2016). [2] Milot, Eperon, Green, Snaith, Johnston, Herz, J. Phys. Chem. Lett. 7, 4178 (2016). [3] Rehman, Milot, Eperon, Wehrenfennig, Boland, Snaith, Johnston, Herz, Adv. Mater. 27, 7938 (2015). [4] McMeekin, Sadoughi, Rehman, Eperon, Saliba, Hörantner, Haghighirad, Sakai, Korte, Rech, Johnston, Herz, Snaith, Science 351, 151 (2016). [5] Rehman, McMeekin, Patel, Milot, Johnston, Snaith, Herz, Energy Environ. Sci. 10, 361 (2017).

Organic solar cells with >12% PCEs Yongsheng Chen The College of Chemistry & School of Materials Science and Engineering Nankai University Tianjin, CHINA Email: yschen99@nankai.edu.cn Polymer/organic photovoltaic has been thought as one of the promising technology to face the increasing energy and environmental issues. In this talk, a series of high performance oligomer-like organic small molecules and their OPV devices will be discussed. Particularly, tandem cells using all small molecules with >12% PCEs will be presented in details. [1] "Solution-processed organic tandem solar cells with power conversion efficiencies >12%", Nature Photon, 2016, doi:10.1038/nphoton.2016.240 [2] "A Series of Simple Oligomer-like Small Molecules Based on Oligothiophenes for Solution-Processed Solar Cells with High Efficiency", J. Am. Chem. Soc., 2015, 137, 3886 [3] "Small-molecule solar cells with efficiency over 9%", Nature Photon., 2015, 9, 35. [4] "High performance photovoltaic applications using solution processed small molecules", Acc. Chem. Res, 2013, 46, 2645. [5] "Solution-Processed Organic Solar Cells Based on Dialkylthiol-Substituted Benzodithiophene Unit with Efficiency near 10%", J. Am. Chem. Soc., 2014, 136, 15529.

Organic photovoltaics (OPV) can lead to a low cost and short energy payback time alternative to existing photovoltaic technologies. However, to fulfill this promise, power conversion efficiencies must be improved and simultaneously the architecture of the devices and their processing steps need to be further simplified. In this talk we will present a simple solution-based technique that leads to the electrical doping of semiconducting polymer films over a limited depth. We will also show how that new processing technique can be employed to fabricate efficient single layer organic photovoltaic devices in which the functions of hole-and electron-collection are integrated in specific regions of the active layer near the electrodes. “Solution-based electrical doping of semiconducting polymer films over a limited depth,” V. A. Kolesov, C. Fuentes-Hernandez, N. Aizawa, F. A. Larrain, W.-F. Chou, M. Wang, A. Perrota, S. Choi, S. Graham, G. C. Bazan, T.-Q. Nguyen, S. R. Marder and B. Kippelen, Nature Materials (2016). Doi: 10.1038/nmat4818

Organometallic halide perovskite solar cells (PSCs) are extremely promising novel materials for thin-film photovoltaics, exhibiting efficiencies over 22% on glass and over 17% on foil ^{1, 2} . First, a sheet-to-sheet (S2S) production of PSCs and modules on 152x152 mm² substrates was established, using a combination of sputtering, e-beam evaporation, slot die coating and thermal evaporation (average PCE of 14.6 ± 1.3 % over 64 devices, more than 10% initial PCE on modules). Later the steps towards a roll-to-roll production will be investigated, starting from the optimization of the stack to make it compatible with a faster production at low temperature. A water based SnO_x nanoparticles dispersion was used as solution processable ETL, and the deposition process was scaled-up from spin coating to R2R slot die coating on a 300 mm wide roll of PET/ITO. R2R production is often carried out in ambient atmosphere and involve the use of large volumes of materials, thus a first point is the development of a green solvent and precursor system for the perovskite layer to prevent the emission of toxic compound in the environment. The first results on device fabrication are encouraging, which allow partial R2R manufacturing of flexible PSC (R2R coating of SnO_x and perovskite, S2S for Spiro-OMeTAD and gold) with stabilized PCE of 12.6%, a remarkable value for these novel devices. This result can be considered an important milestone towards the production of efficient, low cost, lightweight, flexible PSC on large area.

We report on high efficient multi-junction small-molecule organic p-i-n solar cells with an efficiency of up to 13.2% efficiency with an active area of 1.1 cm² from our labs. Furthermore, we discuss in detail the photon loss mechanisms of triple stacked solar cells of 12.5% efficiency by means of IPCE measurements in combination with an optical model. Additionally, we report about the latest findings from our fully integrated roll-to-roll vacuum production process of smallmolecule organic p-i-n tandem solar cells. Modules from Heliatek’s roll-to-roll production show efficiencies of 7.7% on the active area of 4629cm₂ with a fill factor of 66%. Modules from production were analyzed via IPCE-measurement showing a good agreement with the optical calculation mentioned above. This shows that organic layer sequences developed, tested, and analyzed on a lab tool were successfully transferred to a roll to roll vacuum machine.

Despite having surpassed 10% power conversion efficiency (PCE), widely held as the threshold for commercial viability, high performance organic photovoltaics (OPVs) are still mostly constrained to lab-scale devices fabricated by spin coating. Efforts to produce scalable printed OPVs trail significantly in efficiency, highlighting the need to better understand the processing-morphology-performance relationship in the context of linear printing processes. Here we investigate the OPV system PTB7-Th/PC71BM, which has demonstrated >10% PCE via spincoating but only exhibits ~1% PCE when roll-to-roll printed. Of particular interest is the ubiquitous alcohol wash post-treatment applied to the dried active layer, which induces a significant improvement in device performance, and its crucial role for printed films. While it has been speculated that the primary utility of the alcohol post-treatment is to remove the additive 1,8-diiodooctane (DIO) residue in the dried film, we find here that the wash process itself dramatically impacts morphology in printed films regardless of the presence of DIO. Here we employ various x-ray characterization techniques to probe phase separation, crystallinity, and molecular orientation, as well as in-situ grazing-incidence x-ray diffraction (in-situ GIXD) to monitor morphological evolution during the isopropanol post-treatment process. It is discovered that isopropanol induces significant donor polymer alignment and enhanced π-π degree of crystallinity. Through the understanding gained in this study, we are able to achieve a roll-to-roll printed OPV with 5% PCE, which is to our knowledge the highest reported performance for a roll-to-roll printed single junction photoactive layer on a flexible substrate.

The performance of polymer/perovskite solar cells (PSCs/PVKSCs) is highly dependent on the interfacial contact between the active layer and electrodes. Water/alcohol soluble interfacial materials, which enable orthogonal processing of high-performance multi-layer PSCs can greatly improve the interfacial contact as well as device performance. Traditional interfacial materials are not compatible with the large-area processing of PSCs using roll-to-roll techniques. Here, we present a series of self-doped interfacial materials with controlled doping properties and high mobility for the interface optimization of PSCs. Self-doped interfacial materials containing n-type conjugated backbone and polar side chains are prepared. It was shown that neutral amino groups undergo photo-induced doping process while the bromide-quaternized groups employ a self-doped mechanism.1 Further study on the counterions of the self-doped interfacial materials shows that the counterions can also induce different self-assembling and doping behavior with different strength, leading to varied charge-transporting properties. 2 More importantly, these self-doped interfacial materials can enable high-performance (>10%) PSCs and still work efficiently in varied thickness, which match well with the requirement of the fabrication of large-area PSCs. Based on the development of self-doped interfacial materials, a high-performance interconnecting layer for tandem solar cells was also developed, which can boost the power conversion efficiency (PCE) of tandem solar cells to 11.35%.3 Moreover, these interfacial materials can passivate the surface traps of perovskite to improve the electron extraction properties of PVKSC, leading to high-performance PVKSCs even when the thickness of interfacial material is more than 200 nm.4 The successful development of self-doped interfacial materials offers a better processing window for potential fabrication of PSCs/PVKSCs using large-area processing method. 1 J. Am. Chem. Soc. 2016, 138, 2004-2013. 2 Mater. Horiz. 2017, 4, 88-97. 3 Adv. Mater. 2016, 28, 4817-4823. 4 Adv. Energy Mater. 2016, 1501534.

The fabrication of organic photovoltaic modules via printing techniques has been the greatest challenge for their commercial manufacture. Current module architecture, which is based on a monolithic geometry consisting of serially interconnecting stripe-patterned sub-cells with finite widths, requires highly sophisticated patterning processes that significantly increase the complexity of printing production lines and cause serious reductions in module efficiency due to so-called ‘aperture loss’ in series connection regions. In this study, we demonstrate an innovative module structure that can simultaneously reduce both patterning processes and aperture loss. By using a charge recombination feature that occurs at contacts between electron/hole transport layers, we devise a series connection method that facilitates module fabrication without patterning the charge transport layers. With the successive deposition of component layers using slot-die and doctor-blade printing techniques, we achieve a high module efficiency reaching 7.5% with area of 4.15 cm2.

In polymer solar cells (PSCs), molecular design and modulation of chemical composition of the active layer materials are of critical importance for enhancing power conversion efficiencies (PCEs). In our previous work, a PCE of 11.2% was demonstrated by using a new combination of a polymer donor named PBDB-T and a small molecular acceptor (SMA) named ITIC. In order to optimized photovoltaic performance of the PBDB-T:ITIC-based PSCs, subtle chemical modifications of end-groups (EGs) were applied to precisely optimize the molecular energy level of ITIC. By successively introducing one- and two- methyl substituents, the lowest unoccupied molecular orbital (LUMO) levels of the two new acceptors (IT-M and IT-DM) were raised by 0.04 eV and 0.08 eV, respectively, compared to ITIC. Hence, improved open-circuit voltages (VOC) of 0.94 V and 0.97 V were obtained in the corresponding PSCs. Benefiting from the optimized molecular energy levels in the PBDB-T:IT-M-based blend, a PCE of 12.05% was obtained. Furthermore, we also introduced the third component Bis-PCBM[70] to enhance light absorption of the PBDB-T:IT-M blend in the short wavelength region. In the ternary PSCs based on PBDB-T:IT-M:Bis-PCBM[70], a higher PCE of 12.2% was achieved.

Organic semiconductors (OSCs) have found numerous applications in thin film electronic devices, including displays, sensors, lighting, and solar cells. OSCs offer the advantage that they can be modified by synthetic chemists to fulfill specific needs, and that they are not limited to being made from single elements or compositional alloys. For example, organic photovoltaics (OPVs) have reached nearly 13% power conversion efficiency (PCE) in small area devices using traditional polymer-fullerene blends, yet non-polymer and non-fullerene composites are now also showing PCEs above 10%. The flexibility offered by synthetic manipulation also presents a challenge: progress towards the discovery of next-generation, high-performance materials can be stifled by the bottleneck of device optimization through process engineering. High-throughput screening techniques that provide high fidelity performance metrics can circumvent this problem and will become important tools to accelerate material development. Here, we introduce such a tool, based on unique microwave conductivity capabilities, and illustrate a cost- and time-effective approach to evaluate the potential of promising new materials, independent of their bulk (i.e., device optimized) thin-film performance. We demonstrate the power of this approach, by correlating figures of merit from our screening tool to the OPV device performance for a library of current state-of-the-art OSCs, based on both polymer and small molecule chemical structure motifs. Finally, in the context of polymeric materials, we highlight the sensitivity of the screening process to physicochemical properties (e.g., molecular weight) and suggest that our tool can be employed for batch-to-batch quality control.

The initial steps in organic photovoltaic cell (OPV) operation involve the formation of neutral excitons through photo absorption, exciton diffusion to and separation into free charges at the donor acceptor interface.1, 2As the usable solar spectrum spans a large range from the visible to the infra-red (IR), an obvious direction for improved light harvesting is to synthesize donor and acceptor materials with complementary absorption. In such devices, specifically those involving polymer donors and small molecule acceptors, both charge transfer from donor and acceptor moieties, and energy (exciton) transfer from high band gap to low band gap material are possible. Here we show that when charge and exciton transfer processes are present, the co-existence of excitons in both domains can cause a loss mechanism. Charge separation of excitons in a low band-gap polymer is hindered due to exciton population in the larger band-gap acceptor domains. Our results further show that excitons in the lower bandgap material should have a relatively long lifetime compared to the transfer time of excitons from the higher band gap material, in order to contribute to the charge separation. These observations provide significant guidance for design and development of new materials in OPV applications.

We have deposited perovskite solar cells with a bandgap of 1.68 eV onto heterojunction silicon solar cells that by themselves have an efficiency of 21% to create a 1 square centimeter monolithic tandem solar cell with an efficiency of 25.3%. We have also made all-perovskite tandems using a new ABX3 perovskite composition containing a mixture of tin and lead on the B site that have greater than 20% efficiency. With solar cells packaged between two sheets of glass with rubber edge seals, we have passed the industry standard 1000 hour 85°C 85% humidity damp heat test as well as 200 cycles between 85°C and -40°C. One of the keys to obtaining high efficiency and stability was optimizing the composition of cesium and formamidinium on the A site and iodine and bromine on the X site. We will show how light -induced phase separation occurs when there is too much bromine in the films. Another crucial step towards improving stability is the use of atomic layer deposition to deposit a tin oxide buffer layer on the perovskite that enables the sputter deposition of an indium tin oxide transparent electrode. ITO is less reactive with perovskites than the metals that are typically used in perovskite solar cells. The ALD layer has minimal parasitic absorption and prevents shunting. Our progress towards achieving 30% power conversion efficiency and passing even more aggressive stability tests will be presented.

The rapid rise of power conversion efficiency of metal-halide perovskite solar cells beyond 20 % has drawn huge attention. Recent certified efficiencies, however, have been marked as “unstabilized” as perovskite solar cells tend to show a hysteretic behaviour during current density-voltage (J-V) measurements. This leads to deviating results for varying scan parameters and conditions, which challenges reliable and comparable results. In particular, the extent of this behaviour is highly dependent on device preparation method, architecture, device history, and more importantly on measurement preconditions and scan rate. Thus, the demand for reliable stabilized values arises which are reproducible and comparable among different laboratories. Here we introduce an adaptive tracking of the maximum power point and the open circuit voltage. We compare these values with device characteristics derived from standard J-V measurements. Furthermore, we discuss the challenges of a correct efficiency determination and provide the algorithms for easy implementation in existing measurement systems.

We have analyzed microstructures of perovskite layers deposited with different composition by controlling X-ray incident angle from 0.05 to 0.5, corresponding to near-surface and full-depth from surface, respectively. The patterns in the perovskite layers will be discussed in detail by combing with a high resolution TEM. In addition, alternative materials for electron- and hole-transporting layers will be introduced, because it would be important to solve several practical issues such as stability and flexibility. Sn-based oxides for the use in electron-transporting layer (ETL) and a low temperature solution-processed copper thiocyanate (CuSCN) as an inorganic HTL were applied to PSCs

Inorganic organic metal halide perovskite materials have been investigated for several technological applications, such as photovoltaic cells, lasers, photodetectors and light emitting diodes (LEDs), either in the bulk form or as colloidal nanoparticles. Recently, all inorganic Cesium Lead Halide (CsPbX₃, X=Cl,Br, I) perovskite quantum dots (PQDs) were reported with high photoluminescence quantum yield with narrow emission lines in the visible wavelengths. Here, green-emitting perovskite quantum dots (PQDs) prepared by a synthetic method based on a mixture of oleylamine and oleic acid as surfactants were applied in the electroluminescent layer of hybrid LEDs in combination with two different conjugated polymers: polyvinylcarbazole (PVK) or poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO). The performance of the diodes and the emission color tuning upon dispersion of different concentrations of the PQDs in the polymer matrix is discussed. The presented approach aims at the combination of the optical properties of the PQDs and their interaction with wide bandgap conjugated polymers, associated with the solution processing ability of these materials.

Recently, researchers have focused more to design highly efficient flexible perovskite solar cells (PVSCs), which enables the implementation of portable and roll-to-roll fabrication in large scale. Here, we demonstrated that vacuum-assisted thermal annealing can be used to control the composition, morphology, and thus the quality of the perovskite films formed from the precursors of PbCl2 and CH3NH3I. Using our vacuum-assisted thermal annealing approach to completely remove the chlorine byproduct, pure, pore-free planar CH3NH3PbI3 films with enhanced morphology can be readily formed for high efficiency PVSCs with high stability and reproducibility. In addition, we will report new room temperature approaches for forming PVSCs. Regarding the hole transport layer (HTL), NiOx is a promising material for candidate for fabricating efficient PVSCs. Here, we demonstrate the flawless and surface-nanostructured NiOx film from a simple and controllable room-temperature solution process. Meanwhile, we will propose a new room temperature scheme formation of perovskite films with the features of PbI2 residue-free, large grain-sizes, and highly crystalline. We further layout the design rules for the broad, rational extension of our scheme to form high-quality perovskite films. Using our approach, a room-temperature processed PVSC is obtained with no hysteresis, high power conversion efficiency of about 18%, which is the best of the PVSCs fabricated by low-temperature techniques to date. Additionally, the device is very stable with performance maintance of 95% after 1000 hours. This work contributes to the large-sale and low-cost production of PVSCs with high device performances.

Owing to the recently developed nonfullerene small molecule acceptors, the best power conversion efficiency (PCE) of solution-processable organic solar cells (OSCs) has been boosted up to over 12%[1], which makes this technology an economically viable contender for commercialization. Along with the steady progress in PCE achieved by spin-coating photovoltaic materials with chlorinated solvents in protective atmosphere, a central issue in the development of OSCs is pursuing a greener and simpler manufacturing protocol[2], which particularly allows for large-area processing in ambient air. Particularly, it is still a great challenge to replace halogenated solvents with halogen-free, low-toxicity solvents to achieve high-efficiency nonfullerene OSCs. Here we show that ~11.6% efficiency is achieved in nonfullerene OSC device based on PBDB-T:IT-M[3] by using a non-halogenated solvent combination. Moreover, the device parameters were correlated to the morphology investigated by synchrotron radiation grazing-incidence wide-angle X-ray scattering (GIWAXS), resonant soft X-ray scattering (R-SoXS), and differential scanning calorimetry (DSC). We observed a monotonic correlation between the average composition variations and photovoltaic device characteristics across all processing protocols in this record-efficiency material system. This correlation is indeed universal for OSC, irrespective of acceptor materials used (fullerenes, nonfullerene molecular acceptor, or conjugated polymers) and fabrication methods used (spin-coating or blade-coating).[1-5] We believe this nonhazardous solvent approach will be also applicable in the large area roll-to-roll coating and industrial scale printing of high-efficiency OSCs in air. Reference [1] Li, S.; Ye, L.; Zhao, W.; Zhang, S.; Mukherjee, S.; Ade, H.; Hou, J., Energy-Level Modulation of Small-Molecule Electron Acceptors to Achieve over 12% Efficiency in Polymer Solar Cells. Adv. Mater. 2016, 28 (42), 9423-9429. [2] Ye, L.; Xiong, Y.; Yao, H.; Gadisa, A.; Zhang, H.; Li, S.; Ghasemi, M.; Balar, N.; Hunt, A.; O’Connor, B. T.; Hou, J.; Ade, H., High Performance Organic Solar Cells Processed by Blade Coating in Air from a Benign Food Additive Solution. Chem. Mater. 2016, 28 (20), 7451-7458. [3] Ye, L.; Zhao, W.; Li, S.; Mukherjee, S.; Carpenter, J. H.; Awartani, O.; Jiao, X.; Hou, J.; Ade, H., High-Efficiency Nonfullerene Organic Solar Cells: Critical Factors that Affect Complex Multi-length Scale Morphology and Device Performance. Adv. Energy Mater. 2017, 7, 1602000. [4] Ye, L.; Jiao, X.; Zhang, S.; Yao, H.; Qin, Y.; Ade, H.; Hou, J., Control of Mesoscale Morphology and Photovoltaic Performance in Diketopyrrolopyrrole-Based Small Band Gap Terpolymers. Adv. Energy Mater. 2017, 7, 1601138. [5] Ye, L.; Jiao, X.; Zhao, W.; Zhang, S.; Yao, H.; Li, S.; Ade, H.; Hou, J., Manipulation of Domain Purity and Orientational Ordering in High Performance All-Polymer Solar Cells. Chem. Mater. 2016, 28 (17), 6178-6185.

Perovskite solar cells (PSCs) suffer from decomposition of the active material in the presence of moisture or heat. In addition, the corrosion of metal electrodes due to halide species needs to be overcome.[1,2] Here, we introduce ALD-grown tin oxide (SnOx) as impermeable electron extraction layer (EEL), which affords air resilient and temperature stable MAPbI3 PSCs. Being conductive, SnOx is positioned between the metal electrode and the perovskite. Its outstanding permeation barrier properties protect the perovskite against ingress of moisture or migrating metal atoms, while simultaneously the metal electrode is protected against leaking halide compounds.[2] Therefore, SnOx is also excellently suited to sandwich and protect ultra-thin metal layers (Ag or Cu) as cost efficient Indium-free semitransparent electrodes (SnOx/metal/SnOx) in PSCs. Using photoelectron spectroscopy, we unravel the formation of a PbI2 interfacial layer between a SnOx EEL and the perovskite. The resulting interface dipole between SnOx and the PbI2 depends on the choice of oxidant for ALD (water, ozone, oxygen plasma). SnOx grown by using ozone affords hysteresis-free devices with a stable efficiency of 16.3% and a remarkably high open circuit voltage of 1.17 V.[3] Finally, we fabricated semitransparent PSCs with efficiency >11% (Tvis = 17%) and an astonishing stability > 4500h under ambient conditions (>50% RH) or elevated temperatures (60°C).[4] [1] Y. Kato et al., Adv. Mater. Interf. 2015, 2, 150019 [2] K. Brinkmann et al., Nat. Commun. 8, 13938 [3] T. Hu et al. Adv. Mat. (submitted) [4] J. Zhao et al. Adv. Energ. Mat. (in press)

Absorption edge of perovskite (PVK) solar cells consisting of MAPbI3 is 800nm. According to our simulation, light harvesting in the area of near IR is also necessary for enhancing the efficiency more. We have already reported that mixed metal perovskite (MAPbSnI3) shows photo-conversion in IR region (1-6). The short circuit current (Jsc) was high, reaching to 30 mA/cm2 because of the wide range of light harvesting. However, the open-circuit voltage (Voc) was lower than 0.3 V and the estimated voltage loss was 0.6-0.7 V, which was much larger than that of MAPbI3 (0.4 V), suggesting the presence of high density charge recombination center. We found that Ti-O-Sn bonds formed at the interface between Tiania and MAPbSnI3 layer, create trap states, resulting in increasing charge recombination at the interfaces. The surface trap density and the trap depth was quantitatively monitored by thermally stimulated current methods. When the Ti-O-Sn linkage was formed at the interface between TiO2 and PVK, the trap density increased by one order of magnitude. The interface was analyzed by XPS and confirmed that Ti-O-Sn linkage was formed. After removing the Ti-O-Sn bond at the interface between TiO2 and MAPbSnI3, the efficiency drastically increased from 4.0 % to 13.8 % and the stability was improved. It was proved that interface architecture is quite important for enhancing the MAPbSnI3 solar cells. References 1. S. Nakabayashi, et al., J. Photonics for Energy; 2015, 5, 057410. 2. Y. Ogomi, et al., J. Phys. Chem. Lett. 2014, 5, 1004-1011.

The formation of pinhole-free perovskite photoactive films with full surface coverage has been a tremendous challenge for up-scaling planar perovskite solar cells (PSCs) while maintaining their high power conversion efficiencies (PCEs). Particularly, a significant mismatch between the surface energies of a hydrophilic perovskite precursor solution and a hydrophobic organic charge transport layer (CTL) has been a major cause for the poor and random surface coverage of perovskite photoactive films, which drastically reduces the scalability and reproducibility of PSCs. Here, we report a universal method to create extremely compact perovskite photoactive films on a variety of hydrophobic CTLs. By introducing an amphiphilic conjugated polyelectrolyte as an interfacial compatibilizer, we succeed in improving the wettability of perovskite precursor solutions on hydrophobic CTLs and fabricating perovskite photoactive films over large areas. Our approach enables the scalable fabrication of planar PSCs with large areas (1 cm2, PCE of 17%) while preserving nearly 90% of the PCEs of the corresponding small-area devices (PCE of 19%).

The kinetics at contacts plays a crucial role in sandwich-type thin-film devices based on organic semiconductors. This is of particular importance in organic and perovskite solar cells where selective contacts that are able to efficiently collect majority carriers, simultaneously blocking minority carriers, are desired. Despite the vast progress made, a comprehensive understanding, needed for developing new electrode materials to improve and optimize device performance is still lacking. A key parameter for obtaining information about processes taking place at the contacts is the effective surface recombination velocity.[1] However, means to quantitatively measure surface recombination velocities at contact interfaces in sandwich-type thin-film devices based on organic semiconductors are lacking. The Charge Extraction by a Linearly Increasing Voltage (CELIV) technique is one of the most common methods to measure the charge transport properties in organic semiconductor devices. In this work, we show how CELIV can be used to determine surface recombination velocities at selective and/or blocking contacts in thin-film devices. The analytical framework behind the method is presented, and confirmed by numerical drift-diffusion simulations. We furthermore demonstrate the method on organic semiconductor devices, employing TiO2 and SiO2 as cathode buffer layers. The method allows for an increased understanding of contact properties in sandwich-type thin-film devices based on organic semiconductors. [1] O. J. Sandberg, A. Sundqvist, M. Nyman, and R. Österbacka, Phys. Rev. Appl. 5, 044005 (2016).

In any photovoltaic device, efficient energy conversion results from a competition between light harvesting, charge separation and transport, and charge recombination. Devices based on disordered materials such as solution processed molecular, inorganic and hybrid semiconductors, despite showing impressive advances in performance recently, typically show greater recombination losses than traditional crystalline semiconductor devices. The impact of non-radiative recombination on open-circuit voltage can be quantified precisely using luminescence techniques, but the method does not indicate the microscopic origin of the recombination nor its impact on overall solar cell performance. In this work, we use a variety of complementary experimental techniques and simulation to correlate the measured voltage losses to the underlying recombination mechanism in different types of solar cell including organic heterojunctions, lead halide perovskites and solution processed inorganic devices. We will focus on the impact of structural and energetic disorder, selectivity of contacts, density and energy of defect states and the competition of charge separation with recombination. We will comment on the extent to which disorder controls the losses to recombination, and address the question of whether large recombination losses are unavoidable in molecular materials.

The efficiency with which photogenerated free carriers are extracted in excitonic solar cells is governed by the interactions between a number of material specific and device level properties and parameters: recombination dynamics, faster and slower carrier mobilities, contact potentials, etc. This complexity is inherent in disordered excitonic semiconductors, and understanding the underlying structure-property relationships is an ongoing endeavour in the field of organic solar cells. Questions such as – do higher mobility semiconductors necessarily deliver improved charge collection; how does supressed bimolecular recombination lead to fill factor maintenance especially at higher input irradiances [1]; or, how do we achieve high fill factors and efficiencies in thick junctions more suited to viable manufacturing [2]? In my talk I will examine some of the latest thinking in this area [3], and present data from a suite of emerging experimental techniques such as intensity dependent photocurrent, resistant dependent photovoltage and related extraction methodologies. I will also discuss recent findings on the interrelationship between the efficiency with which free charges are extracted and charge separated state formation – the two possibly connected through entropic considerations [4]. [1] “The impact of hot charge carrier mobility on photocurrent losses in polymer-based solar cells”, B. Philippa, M. Stolterfoht, P. L. Burn, G. Juska, P. Meredith, R. D. White & A. Pivrikas, Scientific Reports, 4, 5695 (2014). [2] "Efficient, large area, and thick junction polymer solar cells with balanced mobilities and low defect densities." A. Armin, M. Hambsch, P. Wolfer, H. Jin, J. Li, Z. Shi, P. L. Burn, and P. Meredith, Advanced Energy Materials, 5, 1401221 (2015). [3] “Impact of charge transport on current-voltage characteristics and power conversion efficiency of organic solar cells”, U. Wurfel, D. Neher, A. Spies & S. Albrecht, Nature Communications, 6:6951 (2015). [4] “Slower carriers limit charge generation in organic semiconductor light harvesting systems”, M. Stolterfoht, A. Armin, S. Shoaee, I. Kassal, P.L. Burn & P. Meredith, Nature Communications, 7, 11944 (2016).

Intrinsic photodegradation of organic solar cells, theoretically attributed to C-H bond rearrangement/breaking, remains a key commercialization barrier. This work presents, via dark electron paramagnetic resonance (EPR), the first experimental evidence for metastable C dangling bonds (DBs) formed by blue/UV irradiation of polymer:fullerene blend films in nitrogen. The DB density increased with irradiation and decreased ~4 fold after 2 weeks in the dark. The dark EPR also shows increased densities of other spin-active sites in photodegraded polymer, fullerene, and polymer:fullerene blend films, consistent with broad electronic measurements of fundamental properties, including defect/gap state densities. The EPR and electronic measurements enable identification of defect states, whether in the polymer, fullerene, or at the donor/acceptor (D/A) interface. Importantly, the EPR results indicate that the DBs are at the D/A interface, as they were present only in the blend films. The role of polarons in interface DB formation will also be discussed.

Three-dimensional (3D) lead halide perovskites exhibit impressively long carrier diffusion lengths and low trap densities, while reduced-dimensionality perovskites, such as two-dimensional (2D) and zero-dimensional (0D) perovskite derivatives, possess large exciton binding energies and high photoluminescence quantum yields. These characteristics make the diverse class of perovskite materials ideal for photovoltaics, photodetection, and light emission. Here we discuss our latest advances in growing and understanding the properties of monocyrstalline 3D perovskites, as well as 0D and 2D perovskite derivatives. We also demonstrate the integration of these materials in a range of optoelectronic applications including: monocrystalline perovskite solar cells; simultaneously fast and sensitive photodetectors that can operate in both broadband and narrow-band regimes; and efficient light-emitting diodes. Thus, in these device prototypes, we showcase the importance of crystallinity, dimensionality, and composition for tailoring materials properties, and realizing novel and efficient perovskite optoelectronics.

To date, the most widely employed technique to investigate the crystal structure and morphology of perovskite films have been SEM and X-ray diffraction. Most perovskite films are highly polycrystalline and thus traditional imaging techniques cannot easily isolate single crystallites or determine the statistics of lateral grain size or crystal size and morphology. A further limitation is that both SEM and other scanning probe microscopy techniques are surface-sensitive, with the bulk of the material being largely inaccessible using conventional imaging methods. To gain better insight into a perovskite film, we scan an X-ray beam focused to 400 nm across a sample, while simultaneously recording wide-angle X-ray scattering patterns. Such scanning nanofocus x-ray diffraction (nXRD) techniques have been employed to resolve local variations in structure across a broad range of materials and research fields, however this is the first time they have been applied to a perovskite film. We describe a method to in which each scattering pattern is analysed, allowing a classification to be made of individual perovskite grains according to a specific Miller plane. Using this method, we show that nXRD is able to resolve the extent of individual perovskite grains buried within a polycrystalline film (grain segmentation). We then use nXRD and SEM to demonstrate that the perovskite film coverage can be controlled by varying the temperature of the substrate during spin-coating. We conclude by showing that solar cells with a perovskite layer cast on a substrate held at a relatively high temperature result in devices with higher PCE.

Organic-inorganic perovskites have emerged as an interesting class of materials that have excellent photovoltaic properties for application to solar cells. The power conversion efficiency of perovskite solar cells over 20% has already been realized through systematic optimization of materials and fabrication processes. However, the long-term stability of perovskite solar cells still need to be improved for practical applications. In this study, we introduced a multifunctional benzoquinone (BQ) additive into a precursor solution containing methylammonium iodide (MAI) and lead iodide (PbI2) used for spin-coating of perovskite films. Resulting spin-coated perovskite films containing BQ had the improved perovskite morphology and crystal quality because of intermolecular interaction between MAI and BQ slowing the rate of perovskite crystal formation. Therefore, we obtained the greatly enhanced power conversion efficiency from 10.7% to 15.6%. The reduced charge recombination loss by electron transfer from perovskite to BQ is another source of the improved efficiency. In addition to the efficiency enhancement, the BQ addition led to the extended lifetime about twenty-six times. The lifetime, at which efficiency reduces to 80% of the initial under the one-sun condition (100 mW/cm2 and AM1.5G), reached about 4000 h, one of the longest lifetimes ever reported in perovskite solar cells. The extended lifetime can be explained by the reduced formation of carrier traps originating from metallic lead during solar irradiation as the results of thermally stimulate current measurements. We believe that the present findings offer insight to help obtain efficient, stable organic-inorganic perovskite solar cells for future applications.

We demonstrate how amino-terminated silane monolayers alter the chemical and energetic composition of the TiO2 surface, which controls the interfacial nucleation, growth and energetics of device-relevant, hybrid perovskite (PVSK) thin films. The surface chemistry and energetics of compact TiO2 thin films are modified with a 3-aminopropyltriethoxysilane (APTES) monolayer that can either weakly coordinate Pb2+ ions (–NH2/free base form) or act as a surrogate organic cation (–NH3+/acid form) at the TiO2/PVSK interface, providing for significant differences in the nucleation free energy for the PVSK active layer as a function of NH3+/NH2 ratio. XPS spectra of amine-modified TiO2 surfaces (N 1s core level) demonstrate that we can achieve NH3+/NH2 ratios of between 3:1 and 1:3 depending upon subsequent acid and base treatment, respectively. Methylammonium lead triiodide (MAPbI3) films are incrementally co-evaporated on TiO2, TiO2/APTES-NH3+ and TiO2/APTES-NH2 interfaces, and the chemical composition, growth dynamics and energetics are systematically investigated using in situ X-ray photoelectron spectroscopy (XPS) and UV photoelectron spectroscopy (UPS). The XPS and UPS results reveal that initial nucleation and subsequent growth of the MAPbI3 PVSK film strongly depends on the chemical functionality of the TiO2 surface. The evaporated films display island-like growth on the bare TiO2 surface, which hinders nucleation of the PVSK phase until ca. 15 nm of precursor material is deposited. Conversely, film growth is more layer-by-layer on the amine-modified TiO2 interfaces, which promote nucleation of the PVSK phase within the first ca. 5 nm of deposition. In addition to vacuum evaporated thin films, we show how these TiO2 surface modifications control the morphology and crystallinity of solution-processed PVSK films based on formamidinium and methylammonium organic cations. These studies elucidate the role of TiO2 surface chemistry on the formation mechanism of hybrid PVSK active layers and the interfacial and bulk energetics, which have significant consequences related to the processing and operation of next-generation optoelectronic device platforms.

The multi-junction concept is especially attractive for the photovoltaic (PV) research community owing to its potential to overcome the Schockley-Queisser limit of single-junction solar cells. Tremendous research interests are now focused on the development of high-performance absorbers and novel device architectures for emerging PV technologies, such as organic and perovskite PVs. It has been predicted that the multi-junction concept is able to boost the organic and perovskite PV technologies approaching the 20% and 30% benchmarks, respectively, showing a bright future of commercialization of the emerging PV technologies. In this contribution, we will demonstrate innovative architecture design for solution-processed, highly functional organic and hybrid multi-junction solar cells. A simple but elegant approach to fabricating organic and hybrid multi-junction solar cells will be introduced. By laminating single organic/hybrid solar cells together through an intermediate layer, the manufacturing cost and complexity of large-scale multi-junction solar cells can be significantly reduced. This smart approach to balancing the photocurrents as well as open circuit voltages in multi-junction solar cells will be demonstrated and discussed in detail.

Polymer-based solar cells have made rapid progress in the last decade and are currently attracting a great deal of attention as a next-generation solar cell. Very recently, they have shown a power conversion efficiency (PCE) of more than 10%, which is comparable to that reported for amorphous silicon solar cells. However, it is still required to improve the photovoltaic performance furthermore for practical applications. In this talk, I will demonstrate ternary blend polymer solar cells, which are a new approach to improving the photocurrent generation. We have recently developed ternary blend polymer solar cells based on a wide-bandgap polymer, poly(3-hexylthiophene) (P3HT), a fullerene derivative (PCBM), and a near-IR dye molecule such as a silicon phthalocyanine derivative (SiPc). Such near-IR dye addition can easily expand the light-harvesting wavelength range up to the near-IR region, and hence can boost the photocurrent furthermore. I will demonstrate how molecular design of near-IR dye molecules can control the location in ternary blend solar cells to improve the photocurrent generation effectively. We also have fabricated ternary blend polymer solar cells based on a wide-bandgap polymer, a low-bandgap polymer, and PCBM. This two-donor polymer blend can also expand the light-harvesting wavelength and hence can boost the photocurrent effectively. Efficient exciton harvesting and charge collection can be designed by combining a wide-bandgap crystalline polymer and a low-bandgap amorphous polymer.

Record efficiencies of OPV devices nowadays reach well above 10%. However, their organic nature makes them strongly sensitive to oxygen, light, heat and humidity. We report on long-term stabilization by ternary blending the active layers with small amounts of stabilizing compounds of different classes of antioxidants[1,3], radical scavengers[1] and light stabilizers[2]. Lifetime testing was conducted under ISOS3-degradation conditions on bulk-heterojunction cells containing a wide selection of stabilizers. Microscopic and spectroscopic methods were applied to monitor chemical degradation over time, and the observed differences are discussed in terms of energetic trap states formation within the HOMO/LUMO gap of the photoactive material, morphological and structural changes. Both antioxidants and UV absorbers yielded an increase of the accumulated power generation by over a factor of 3 compared to the reference devices without additive. In both cases, stability improvement was caused by significant reduction of radicals within the photoactive layer, which in turn stabilizes the performance by decreasing exciton recombination. However, stabilization mechanisms of these two classes are quite different, as reflected in the burn-in. While antioxidant-stabilized cells manifested a simultaneous increase of the burn-in period and decrease of decay magnitude, UV-absorber-stabilized cells retained the same burn-in period as the reference. [1] Turkovic V. et al, ACS Applied Materials & Interfaces 6, p 18525 (2014); http://dx.doi.org/10.1021/am5024989 [2] Turkovic V. et al, Journal of Physics D: Applied Physics 49, p 125604 (2016); http://dx.doi.org/10.1088/0022-3727/49/12/125604 [3] Turkovic V. et al, Applied Physics A 122:255 (2016); http://dx.doi.org/10.1007/s00339-016-9758-7

Embedding Semiconductor Quantum Dots (QDs) into hybrid organic-inorganic solar cell holds promises for improving photovoltaic performances. Thanks to their strong coupling with electro-magnetic radiation field, QDs represent paradigmatic photon absorbers. Nevertheless, the quest for suitable charge separating hetero-interfaces is still an open challenge. Within this framework, the excited state interactions between QDs and fullerene derivatives are of great interest for ternary solar cells (polymer:QDs:fullerene). In this work, we investigated the exciton dynamics of core/shell CdSe/CdS QDs both in solution and in blends with fullerene derivative (PCBM). By means of transient optical techniques, we aimed to unveil the dynamics of the QDs-PCBM interaction. Indeed, the observed excited state depopulation of QDs in blends is compatible with an excited state interaction living on picosecond timescale. Through electron paramagnetic resonance, we delved into the nature of this interaction, identifying the presence of charge separated states. The concurrence of these observations suggest a fast electron transfer process, where QDs act as donors and PCBM molecules as acceptors, followed by effective charge separation. Therefore, our experimental results indicate the QDs-PCBM heterointerface as suitable exciton separating interface, paving the way for possible applications in photovoltaics.

P3HT:PCBM is one of the most studied polymer-fullerene system. However the reported power conversion efficiency (PCE) values falls within the range of 4% to 5%. The thin film architecture in OPVs exhibits low PCE compared to inorganic photovoltaic cells. This is mainly due to the low exciton diffusion length that limits the active layer thickness which in turn reduces the absorption of incident light. Several strategies are adapted in order to increase the absorption in the active layer without increasing the film thickness. Inclusion of metal nanoparticles into the polymer layer of bulk heterojunction (BHJ) solar cells is one of the promising methods. Incorporation of metal nanostructures increases the absorption of organic materials due to the high electromagnetic field strength in the vicinity of the excited surface plasmons. In this work, we used ~ 60 nm Au plasmonic structures to improve the efficiency of organic solar cell. The prepared metal nano structures were characterized through scanning electron microscopy (SEM), and UV-Visible spectroscopy techniques. These prepared metallic nanoparticles can be incorporated either into the electron transport layer (ETL) or into the active P3HT:PC₇₁BM layer. The effect of incorporation of plasmonic gold (Au) nanoparticle in the inverted bulk heterojunction organic photovoltaic cells (OPVs) of P3HT:PC₇₁BM fabricated in ambient air condition is in progress. Initial studies shows an 8.5% enhancement in the PCE with the incorporation of Au nanoparticles under AM1.5G light of intensity 1 Sun.

The vertically self-organized concentration profile of the PSS:PEDOT:PFI layer from mesoscale DPD simulations presented in the previous contribution were inversely mapped back into atomistic scale. DFT quantum calculations were then performed to understand the nature of the formation of the PFI:PSS:PEDOT complex. Hydrogen bond bonding energy and deprotonation energy were obtained accordingly. The charge states of PSS polymer chain in this complex and its effects on the HOMO-LUMO (the work function) were discussed. The DFT quantum calculation revealed the formation of complex hydrogen bonding networks leading to the formation of super PFI:PSS:PEDOT structure. PFI was found to be a stronger H donor than PSS. The adding of PFI was found to have the effect of lowering the energy of PSS chain, as the result the HOMO of the PFI:PSS:PEDOT ternary structure was found to be -5.35 eV, lower than the original PSS:PEDOT binary structure. The increasing of the work function from the bottom to the top of the film can therefore be understood as the result of the combining effects of increasing PSS:PEDOT and PFI:PSS ratio in the vertical direction induced by PFI led phase segregation.

A series of star-shaped donor-acceptor oligomers having alkyldicyanovinyl fragments as electron-withdrawing groups, 2,2′-bithiophene as a conjugated π-bridge and either triphenylamine or its modified analogs (9-phenyl-9H-carbazole derivatives or tris(2-methoxyphenyl)amine as electron-donating cores was designed, synthesized and investigated. Variation of the chemical nature of the donor core allowed elucidating the structure-properties relationships for their solubility, absorption spectra, electrochemistry, phase behavior as well as photovoltaic performance in bulk heterojunction organic solar cells as donor materials in their mixtures with PC₇₀BM. The star-shaped molecules based on triphenylamine and tris(2-methoxyphenyl)amine cores have reduced bandgaps, which leads to more efficient absorption of the sun light and better photovoltaic performance.

In this work, we present the results of investigation of thin film hybrid organic-inorganic photovoltaic structures based on flat heterojunction hydrogenated silicon (a-Si:H) and poly(3,4 ethylene dioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) fabricated on polyethylene naphthalate (PEN). Different thicknesses of transparent AL doped Zn:O (AZO) electrodes have been tested on PEN substrate and studied by atomic force microscopy (AFM). The AZO films on PEN substrate were statistically processed to obtain surface morphological characteristics, such as root mean square roughness R_Q, skewness S_K and kurtosis K_U. Performance characteristics of fabricated photovoltaic structures have been measured and analyzed for different thicknesses of the transparent electrodes under standard illumination (AM 1.5 I₀= 100mW/cm²). Structures on flexible substrates show reproducible performance characteristic as their glass substrate counterpart with values of J_SC= 6 mA/cm₂, V_OC= 0.535 V, FF= 43 % and PCE= 1.41%.

In order to cut and decollate silicon for the manufacturing of solar cells and electronic components, commonly blade sawing or nanosecond-based laser processes are used. If the cut needs to be carried out with a high precision and without causing any thermal damage to the surrounding material, ultrashort pulsed laser cutting can be used to deliver a fine and small cutting kerf. The reduction of the kerf width leads to a higher yield per wafer, if single elements need to be cut out. As a result, marginal heat affected zones with minimal edge damages are attainable. Ultrashort pulsed lasers range from pico- to femtoseconds. In order to demonstrate the best pulse duration and ablation strategy for the singling of silicon wafers, the ablation threshold for pulse durations is determined using the Liu’s method. Through this method, the diameter of the ablated geometry is measured, squared and plotted against the peak fluence on a logarithmic scale. With the knowledge of the ablation threshold, various influences on cutting of silicon are compared in order to create a minimal cutting kerf with reduced heat affected zone. With decreasing pulse duration, the surface of the silicon seems to be smoother and ablation is characterized by a sharp ridge. The ablation threshold of silicon depends on the temperature, so a second laser beam for pre-heating of the silicon material is coupled coaxially with the cutting beam. This arrangement is found to improve the ablation behavior of silicon.

The PV performance and aging/stability of organic photovoltaic (OPV) devices based on the well-known system PTB7:[70]PCBM and an alternative air-stable electrode deposited at room conditions are fully studied when the active area is scaled by a factor of 25. On the other hand, the aging/stability processes were also studied through single diode model, impedance spectroscopy and light-beam induced current (LBIC) measurements in accordance with the established ISOS-D1 (dark storage) and ISOS-L1 (illumination conditions) protocols. Results are a good indication that the alternative cathode Field’s metal (FM) cathode works as an encapsulating material and provides excellent PV performance comparable with the common and costly high-vacuum evaporated Al cathode.

Organic materials have become very important in recent years due to their potential use for photovoltaic applications. Among the main advantages of organic semiconductors are their functional and mechanical flexibility, as well as fabrication simplicity. However, these materials usually afford moderate efficiency in organic photovoltaic devices. On the other hand, hydrogenated amorphous silicon (a-Si:H) is a widely known inorganic semiconductor that compared to their organic counterparts has excellent photogeneration and transport properties and it is suitable for large area fabrication of flexible devices. The idea of combining organic semiconductors and amorphous silicon films in hybrid photovoltaic devices is very attractive due to the possibility to complement the useful properties of both material systems. The photovoltaic devices that we study in this work consist of a p-i-n structure, which is also commonly used in inorganic solar cells. In such kind of structures, the light is mainly absorbed in the intrinsic silicon film and the p- and ntype films are used to create an electric field that separates electrons and holes to produce a photocurrent. In this work, we use an organic material (PEDOT:PSS) to replace the p-type inorganic film in amorphous silicon p-i-n structure. It is widely known, that PEDOT:PSS based organic film is highly transparent and its conductivity can be modified e.g. immerse in a solvent type. Here we present the results of experimental investigation of the effect of isopropanol (IPA) treatments in p-type (PEDOT:PSS) organic layer on characteristics of hybrid solar cell structure.