This PDF file contains the front matter associated with SPIE Proceedings Volume 9942, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

The integration of planar-type perovskite (E_g ~ 1.5 eV) solar cells (PSCs) with a bulk-heterojunction (BHJ) composite comprising a near-infrared (NIR) absorbing conjugated polymer (E_g < 1.4 eV) and a fullerene derivative is a promising approach to overcoming the narrow absorption limit of typical PSCs. Nevertheless, integrated solar cells (ISCs) suffer from low fill factors (FFs) and inefficient NIR harvesting, mainly due to poor charge transport in the BHJ films. Here, we successfully demonstrate highly efficient P-I-N perovskite/BHJ ISCs with an enhanced FF and improved NIR harvesting by introducing a novel n-type semiconducting polymer and a new processing additive into the BHJ films. The optimized ISCs exhibit a power conversion efficiency (PCE) of 16.36%, which far surpasses that of the reference PSCs (~ 14.70%) due to the increased current density (J_sc ~ 20.04 mA cm^-2) resulting from the additional NIR harvesting. Meanwhile, the optimized ISCs maintain a high FF of 77% and an open-circuit voltage (V_oc) of 1.06 V. These results indicate that this approach is a versatile means of overcoming the absorption and theoretical efficiency limits of state-ofthe- art PSCs.

Impact of structural heterogeneity in solar absorber layers Michael F Toney SLAC National Accelerator Laboratory Structural and morphological heterogeneity is common in thin film and emerging solar cell absorber layers, including organic photovoltaic bulk heterojunctions (OPV BHJs), hybrid organic-inorganic perovskites (HOIP), and Cu2ZnSn(S,Se)4 (CZTSSe), and has a significant impact on the (opto)electronic heterogeneity and hence absorber properties. In this talk I will use X-ray based methods, including scattering and spectroscopies, to characterize and quantify the heterogeneity in OPV BHJs and HOIP absorber layers. The BHJ films are blends of the small molecule X2 and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) where it has been established that there are three distinct region of the films – pure PC71BM, pure X2 and intimately mixed X2:PC71BM. This talk will show how the absolute concentration of the mixed phase can be used to explain the large PC71BM:X2 composition range where good performance is observed [1]. The talk will also show that spin cast CH3NH3PbI3 films consistent of both crystalline and amorphous regions, which can explain previous heterogeneity in the PL imaging [2]. [1] Huang et al., Adv. Energy Mater. 4, 1301886 (2014). [2] deQuilettes et al., Science 348, 683 (2015).

The power conversion efficiencies (PCEs) of bulk heterojunction organic photovoltaic (OPV) devices have been reported more than 10%. Recently, in our group, we have achieved a PCE of greater than 11% with an inverted device geometry (device area 0.1 cm2) using a ternary blend comprising, an organic donor polymer, small molecule, and PC71BM, as an active layer. However, the device performance of OSC suffers significant drop with the device area scaling up due to sheet resistance of transparent electrode. In this work, we have used a thin layer of metal grid on top of transparent electrode to reduce the sheet resistance. Using this strategy, we fabricated inverted organic photovoltaic devices with an active layer composed of a ternary blend of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-co-3-fluorothieno[3,4-b] thiophene-2-carboxylate] (PTB7-Th) and small molecule (BTR)1 as the donors and PC71BM as the acceptor and we have achieved the PCE of greater than 8% for square centimetre active area devices. We also studied the role of metal grid thickness as well as geometry and annealing of active layer on the performance of OSCs. 1. K. Sun, Z. Xiao, S. Lu, W. Zajaczkowski, W. Pisula, E. Hanssen, J. M. White, R. M. Williamson, J. Subbiah, J. Ouyang, A. B. Holmes, W. W. H. Wong, D. J. Jones, Nat. Commun. 2015. (DOI: 10.1038/ncomms7013).

This presentation describes my group’s efforts to understand the molecular and microstructural basis for the mechanical properties of organic semiconductors for organic photovoltaic (OPV) devices. Our work is motivated by two goals. The first goal is to mitigate mechanical forms of degradation of printed modules during roll-to-roll fabrication, installation, and environmental forces—i.e., wind, rain, snow, and thermal expansion and contraction. Mechanical stability is a prerequisite for inexpensive processing on flexible substrates: to encapsulate devices in glass is to surrender this advantage. The second goal is to enable the next generation of ultra-flexible and stretchable solar cells for collapsible, portable, and wearable applications, and as low-cost sources of energy—“solar tarps”—for disaster relief and for the developing world. It may seem that organic semiconductors, due to their carbon framework, are already sufficiently compliant for these applications. We have found, however, that the mechanical properties (stiffness and brittleness) occupy a wide range of values, and can be difficult to predict from molecular structure alone. We are developing an experimental and theoretical framework for how one can combine favorable charge-transport properties and mechanical compliance in organic semiconductor films. In particular, we have explored the roles of the backbone, alkyl side chain, microstructural order, the glass transition, molecular packing with fullerenes, plasticizing effects of additives, extent of separation of [60]PCBM and [70]PCBM, structural randomness in low-bandgap polymers, and reinforcement by encapsulation, on the mechanical compliance. We are exploring the applicability of semi-empirical “back-of-the-envelope” models, along with multi-scale molecular dynamics simulations, with the ultimate goal of designing electroactive organic materials whose mechanical properties can be dialed-in. We have used the insights we have developed to demonstrate several new applications for OPV that demand extreme compliance, including biaxial stretching and conformal bonding of whole devices to hemispheres, and devices with ultrathin encapsulation mounted on human skin that survive significant cyclic mechanical deformation in the outdoor environment.

We show inkjet printed state-of-the-art perovskite solar cells with efficiencies of up to 12% which is an important step towards fully printed large scale production of photovoltaic perovskite devices. In comparison, the spin-coated reference achieves 13% efficiency. In both cases, the solar cell absorbers are prepared using a one-step process on a TiO2 compact layer without mesoporous intermediate layer as electron transport material and spiroMeOTAD as hole transport material. Moreover, we show that controlling printing parameters, like drop spacing and size, is essential to optimizing the final perovskite performance. Whereas parameters were initially controlled to be consistent with a final layer thicknesses known from literature, subsequent processes were aimed at also controlling crystallinity and roughness. To demonstrate the homogeneity of the printed devices, light beam induced current measurements (LBIC) were made. To evaluate the quality of the perovskite layer and the charge transfer efficiency in the device, time resolved photoluminescence measurements were conducted on the perovskite with and without electrical transport layers. Light soaking effects were also investigated and evaluated. Important differences between printed and spin-coated devices will be outlined, as well as other relevant parameters to optimize printed device performance.

Hybrid organolead trihalide perovskite (OTP) solar cells have developed as a promising candidate in photovoltaics due to their excellent properties including a direct bandgap, strong absorption coefficient, long carrier lifetime, and high mobility. Most recently, formamidinium (NH2CH=NH2+ or FA) lead iodide (FAPbI3) has attracted significant attention due to several advantages: (1) the larger organic FA cation can replace the MA cation and form a more symmetric crystal structure, (2) the smaller bandgap of FAPbI3 allows for near infrared (NIR) absorption, and (3) FAPbI3 has an elevated decomposition temperature and thus potential to improve stability. Single crystals provide an excellent model system to study the intrinsic electrical and optical properties of these materials due to their high purity, which is particularly important to understand the limits of these materials. In this work, we report the growth of large (~5 millimeter size) single crystal FAPbI3 using a novel liquid based crystallization method. The single crystal FAPbI3 demonstrated a δ-phase to α-phase transition with a color change from yellow to black when heated to 185°C within approximately two minutes. The crystal structures of the two phases were identified and the PL emission peak of the α-phase FAPbI3 (820 nm) shows clear red-shift compared to the FAPbI3 thin film (805 nm). The FAPbI3 single crystal shows a long carrier lifetime of 484 ns, a high carrier mobility of 4.4 cm2·V-1·s-1, and even more interestingly a conductivity of 1.1 × 10-7(ohm·cm)-1, which is approximately one order of magnitude higher than that of the MAPbI3 single crystal. Finally, high performance photoconductivity type photodetectors were successfully demonstrated using the single crystal FAPbI3.

When preparing the active layer film for organic optoelectronic devices, e.g., solar cells, spin-coating is often used for the deposition of the solution of electron donor and acceptor molecules. An alternative, among others, is to use dipcoating, where the substrate is dipped into the solution and subsequently withdrawn, all at coordinated speeds and times. In order to develop knowledge on how the final active layer morphology is influenced by preparation parameters, different coating methods are compared. In this contribution, we report on a comparative study of thin deposited films from a model system. The investigated model system is poly(9,9-dioctylfluorene) (F8, also referred to as PFO) as donor and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₀BM) as acceptor. Combining fluorescence and absorption spectroscopy with atomic force microscopy allows us to conclude that dipcoating offers increased possibilities to manipulate the film morphology, that the transition of the glassy F8 α-phase to the more ordered β-phase is influenced by the dipping speed as well as by the blend ratio, and that the long-wavelength emission of F8 cannot stem from the oxidized keto-F8 only.

In order to examine the interface structure of TiO2/perovskite layer, quartz crystal microbalance sensor (QCM) was used. On the QCM sensor, TiO2 layer was fabricated and the PbI2 solution in Dimethylformamide (DMF) was passed on the QCM sensor to estimate the adsorption density of the PbI2 on the titania2. The amount of PbI2 adsorption on TiO2 surface increased as the adsorption time and leveled off at a certain time. PbI2 still remained even after the solvent only (DMF) was passed on the TiO2 layer on QCM (namely rinsing with DMF), suggesting that the PbI2 was tightly bonded on the TiO2 surface. The bonding structure was found to be Ti-O-Pb linkage by XPS analysis. We concluded that the Ti-OH on the surface of TiO2 reacts with I-Pb-I to form Ti-O-Pb-I and HI (Fig.1 B). The surface trap density was measured by thermally stimulated current (TSC) method. Before the PbI2 passivation, the trap density of TiO2 was 1019 cm3. The trap density decreased to 1016/cm3 after the PbI2 passivation, suggesting that the TiO2 surface trap was passivated with I-Pb-I. The passivation density was tuned by the concentration of PbI2 in DMF, by which TiO2 layer was passivated. Perovskite solar cells were fabricated on the passivated TiO2 layer with various PbI2 passivation densities by one step process (mixture of PbI2 + MAI in DMF). It was found that Jsc increased with an increase in the Ti-O-Pb density. We concluded that the interface between TiO2 and perovskite layer has passivation structure consisting of Ti-O-Pb-I which decreases the trap density of the interfaces and supresses charge recombination. The effect of Cl anion on high efficiency is still controversial when perovskite layer is prepared by one step method from the mixture of MAI and PbCl2. It was found that adsorption density of PbCl2 on TiO2 surface was much higher than that of PbI2 from the experiment using QCM sensor. After the surface was washed with DMF, Cl and Pb were detected. These results suggest that the TiO2 surface was much more passivated by PbCl2 than by PbI2. This may explain partially the high efficiency when the perovskite layer was fabricated by one step process consisting of MAI and PbCl2 solution. We also observed that the crystal size increased with an increase in the amount of Cl anion which of course one of the explanation of the high efficiency. The interface of hole transport layer/perovskite layer, and between perovskite layer /perovskite layer (grain boundary) was passivated with organic amines. The passivation was also effective for increasing Voc and Jsc. This was explained by the results of transient absorption spectroscopy that the charge recombination time between hole transport payer/perovskite layer increased from 0.3 μsec to 60 μsec.

Organic-inorganic (hybrid) lead halide perovskites are taking the lead among the emerging photovoltaics technologies, thanks to the demonstration of power conversion efficiencies exceeding 20 %. Hybrid perovskites have a wide spectrum of desirable properties; they are direct bandgap semiconductors with very high absorption coefficients, high and balanced hole and electron mobility, and large diffusion length. A unique feature of these materials is their versatility in terms of bandgap energy, which can be tuned by simple exchange of their components. In this paper we present vacuum and hybrid deposition routes for the preparation of different organic-inorganic lead perovskite thin films, and their incorporation into efficient solar cells. The influence of the type of organic semiconductors used as hole/electron transport layer in p-i-n solar cells will be presented. We also discuss their electroluminescence properties, either for applications in light-emitting diodes or as a diagnostic tool of the optical and electronic quality of perovskite thin films. Finally, the effect of additives and dopants in the perovskite absorber as well as in the charge selective layers will be described.

Non-ion additive hole-transporting material (HTM) of hydrophobic oligothiophene derivative named DR3TBDTT and triphenylamine derivative of N,N′-di(3-methylphenyl)-N,N-diphenyl-4,4-diaminobiphenyl (TPD) were used for the organic-inorganic hybrid perovskite solar cells. The power conversion efficiency (PCE) was comparable to the device using Li-TFSI doped spiro-MeOTAD. Moreover, the PCE decreases by only 10% after approximately 1000 h without encapsulation, which suggests an alternative method to improve the stability of perovskite solar cells[1-3 ]. Figure 1. Schematic illustration of the energy diagram of the device without lithium salts REFERENCES [1] Zheng, L.; Ma, Y.; Chu, S.; Wang, S.; Qu, B.; Xiao, L.; Chen, Z.;Gong, Q.; Wu, Z.; Hou, X. Nanoscale 6, 8171−8176 (2014). [2] Zheng Lingling, Chung Yao-Hsien, Ma Yingzhuang, Zhang Lipei, Xiao Lixin, Chen Zhijian, Wang Shufeng, Qu Bo and Gong Qihuang, Chem. Commun. 50, 11196-11199 (2014). [3] Ma Yingzhuang, Chung Yao-Hsien, Zheng Lingling, Zhang Danfei, Yu Xiao, Xiao Lixin, Chen Zhijian, Wang Shufeng, Qu Bo, Gong Qihuang, and Zou Dechun, ACS Appl. Mater. Interfaces 7 (12), 6406–6411 (2015)

In recent years, higher power conversion efficiencies have been measured using "push-pull" or Donor-Acceptor (D-A) type compounds designed to specifically address bandgap and energy level requirements. Yet, a strong prescription is fundamentally lacking that improves materials for the set of all critical properties (including exciton diffusion rate and charge transport/ mobility) that combine to provide optimal performance. We will present our newest theoretical models that simulate the morphology-based spectroscopy for a series of squaraines, compounds representative of the total set of D-A type OPV-targets. The theory will describe how morphological and molecular structure influences i) the absorption spectrum, ii) the excited states and iii) the intermolecular charge transfer integral (ICTI). In particular, the ICTI's role in exciton diffusion and carrier mobility will be explored. Using device data that correlates with the ICTI variation, we will explain how this parameter must be considered in future design of new easily-purified, consistently processable, low-band-gap small molecules targeted for large scale OPV manufacture.

We recently reported the high performing molecular donor for OPV devices based on a benzodithiophene core, a terthiophene bridge and a rhodamine acceptor (BTR) [1]. In this work we optimized side-chain placement of a known chromophore by ensuring the thiophene hexyl side-chains are regioregular, which should allow the chromophore to lie flat. The unexpected outcome was a nematic liquid crystalline material with significantly improved performance (now 9.6% PCE), excellent charge transport properties, reduced geminate recombination rates and excellent performance with active layers up to 400nm. Three phase changes were indicated by DSC analysis with a melt to a crystalline domain at 175 oC, transition to a nematic liquid crystalline domain at 186 oC and an isotropic melt at 196 oC. In our desire to better understand the structure property relationships of this class of p-type organic semiconductor we have synthesized a series of analogues where the length of the chromophore has been altered through modification of the oligothiophene bridge to generate, the monothiophene (BMR), the bisthiophene (BBR), the known terthiophene (BTR), the quaterthiophene (BQR) and the pentathiophene (BPR). BMR, BBR and BPR have clean melting points while BQR, like BTR shows a complicated series of phase transitions. Device efficiencies after solvent vapour annealing are BMR (3.5%), BBR (6.0%), BTR (9.3%), BQR (9.4%), and BPR (8.7%) unoptimised. OPV devices with BTR in the active layer are not stable under thermal annealing, however the bridge extended BQR and BPR form thermally stable devices. We are currently optimising these devices, but initial results indicate PCEs >9% for thermally annealed devices containing BQR, while BPR devices have not yet been optimised and have PCEs > 8%. In order to develop the device performance we have included BQR in ternary devices with the commercially available PTB7-Th and we report device efficiencies of over 10.5%. We are currently optimising device assembly and annealing conditions and relating these back to key materials properties. I will discuss the development of these new materials, their materials properties, structural data, and optimised device performance. I will examination of chromophore length on the Nematic Liquid Crystalline properties and on materials development and performance resulting in materials with > 9% PCE in OPV. [1] Sun, K.; Xiao, Z.; Lu, S.; Zajaczkowski, W.; Pisula, W.; Hanssen, E.; White, J. M.; Williamson, R. M.; Subbiah, J.; Ouyang, J.; Holmes, A. B.; Wong, W. W.; Jones, D. J., Nat. Commun. 2015, 6, 6013. DOI: 10.1038/ncomms7013

We present a number of polyfluorene based conjugated polymers with crosslinkable acrylate and oxetane units. These polymers can be crosslinked by free radical polymerization in the case of acrylates and by cationic ring opening polymerization for oxetanes. Upon polymerization densely crosslinked networks are formed which are completely insoluble. We show that the diffusion coefficient of C₆₀ in polyfluorene is reduced by a factor of 1000 by crosslinking. MIS-CELIV measurements are used to monitor changes in the charge carrier mobility upon crosslinking. It shows that using appropriate conditions, e.g. low initiator concentrations or thermal crosslinking, the charge carrier mobility is not reduced by crosslinking. Solution processed three layer organic solar cells were realized with a crosslinkable fluorene based copolymer containing acrylate groups. The efficiency is increased from 1.4% for the reference to 1.8% in the three layer cell with a crosslinked exciton blocking layer. A critical issue of BHJ cells is the instability of the morphology of the polymer:fullerene blend over long operation times at elevated temperature. We present a crosslinkable derivative of the low bandgap polymer PFDTBT which contains oxetane units. BHJ cells with the crosslinked PFDTBT derivative and PCBM were tested in accelerated aging experiments at 100 °C for times up to 100 h. Stabilization was clearly observed in crosslinked BHJ cells compared to the non-crosslinked reference. We show for the first time that oxetane containing polymers can be thermally crosslinked without any added initiator. Initiator free crosslinking is particularly attractive as it avoids the formation of decomposition products, and thus potential electron traps and quenching sites from the initiator.

In this work we compare two different semitransparent inkjet printed electrodes for organic photovoltaic (OPV) applications. We highlight the processing as well as layer properties of the most commonly used silver grid/PEDOT:PSS electrodes and a newly developed inkjet printed silver nanowire (AgNW) mesh. Application of the different electrode types in fully inkjet printed organic solar cells reveals the superior performance of the AgNWs. Using them as bottom and top electrode, semitransparent solar cells with power conversion efficiencies (PCE) of up to 4.3 % are demonstrated. Comparable devices with silver grid electrodes reach a maximum PCE of 3.6 %. We identify shading of the opaque silver grids, which cover ~10 % of the device area, and thermal stress introduced by the curing of the silver grid top electrodes as main factors for the losses. Furthermore, the silver grids do not only lower the short circuit current of the solar cell, but are also visually obstructive.

The newly developed inkjet printed AgNW percolation network electrodes show high transparency of over 90 % at a sheet resistance of less than 20 Ω/□ and a very low haze of less than 3 %. This enables a clear view through semitransparent devices like organic light emitting diodes (OLEDS) or solar cells in which they can be used.

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 the most efficient devices to date, the functions of photocurrent generation, and hole/electron collection are achieved in different layers adding complexity to the device fabrication. In this talk, we present a novel approach that yields devices in which all these functions are combined in a single layer. Specifically, we report on bulk heterojunction devices in which amine-containing polymers are first mixed in the solution together with the donor and acceptor materials that form the active layer. A single-layer coating yields a self-forming bottom electron-collection layer comprised of the amine-containing polymer (e.g. PEIE). Hole-collection is achieved by subsequent immersion of this single layer in a solution of a polyoxometalate (e.g. phosphomolybdic acid (PMA)) leading to an electrically p-doped region formed by the diffusion of the dopant molecules into the bulk. The depth of this doped region can be controlled with values up to tens of nm by varying the immersion time. Devices with a single 500 nm-thick active layer of P3HT:ICBA processed using this method yield power conversion efficiency (PCE) values of 4.8 ± 0.3% at 1 sun and demonstrate a performance level superior to that of benchmark three-layer devices with separate layers of PEIE/P3HT:ICBA/MoOx (4.1 ± 0.4%). Devices remain stable after shelf lifetime experiments carried-out at 60 °C over 280 h.

Organic photovoltaics (OPV) show strong potential for a number of renewable energy applications because of some specifically appealing features (light weight, flexibility, color, …). Over the past decade, the power conversion efficiencies of organic solar cells have strongly risen to values surpassing the 10% threshold, mainly due to strong efforts in chemical engineering of the photoactive components, architectural device optimization and acquisition of fundamental insights in the underlying device physics. As part of the device optimization, the use of conjugated polyelectrolyte (CPE) interfacial layers has been introduced as a popular and powerful way to boost the inherent I-V characteristics. In the presented work, we applied impedance spectroscopy to probe the dielectric permittivity of a series of polythiophene-based CPE interlayer materials as a means to postulate design rules toward novel generation interfacial layers. The presence of ionic pendant groups grants the formation of a capacitive double layer, boosting the charge extraction and device efficiency. A counteracting effect is that the material’s affinity with respect to the underlying photoactive layer diminishes. To enhance the interlayer-photoactive layer compatibility, copolymer structures containing a certain amount of non-ionic side chains are found to be beneficial.

The effects of peripheral alkyl groups and thermal annealing on the exciton quenching efficiency in bilayer porphyrinfullerene thin films has been investigated. The thin film UV-vis absorbance spectra, steady-state fluorescence emission, and thermal properties of three carboalkoxyphenyl porphyrin derivatives have been studied: tetra(4-carbohexoxyphenyl)porphyrin (TCH₄PP), tetra(4-carbo-2-ethylhexoxyphenyl)porphyrin (TCEH₄PP), and tetra(4-carbooctoxyphenyl)-porphyrin (TCO₄PP). The quenching efficiencies of these three derivatives have been calculated from their steady-state emission using pristine spin cast films and films with an evaporated C₆₀ bilayer. Structural analyses have been performed using X-ray diffraction (XRD), UV-vis spectroscopy, and thermal properties were studied using differential scanning calorimetry measurements (DSC). Annealing the films caused significant structural changes as was observed in the UV-vis absorbance spectra and XRD diffraction patterns. Prior to thermal annealing, quenching efficiencies are greatest for the TCH₄PP and TCO₄PP (hexyl and octyl derivatives), which is in agreement with previous bulk quenching experiments to calculate exciton diffusion lengths.¹ After annealing, the hexyl derivative (TCH₄PP) showed the lowest bilayer quenching efficiency and indicated evidence of significant molecular rearrangements.

In this presentation we evaluate the thermal and light-soaking stability of polymer:fullerene bulk heterojunctions (BHJs) based on a donor polymer recently developed by Merck Chemicals. Blade-coated thin films of pure polymer and BHJs incorporating either PC61BM or PC71BM were investigated using atomic force microscopy (AFM), grazing-incidence x-ray diffraction (GIXD), neutron reflectivity (NR), and UV-Visible spectroscopy. The addition of fullerene to the polymer at device-relevant concentrations (25-50% by weight) results in a 7-fold reduction in surface roughness relative to pure polymer films, attributed to a reduction in the pure polymer domain size with increasingly homogeneous polymer:fullerene mixing. Films subjected to accelerated stressing relevant to scalable OPV fabrication—thermal stressing at 120 °C for 1 hour or light-soaking under AM1.5 light for 8 hours—indicate robust stability to stressing, with thin films showing marginal but monotonic increases in roughness with increasing fullerene concentration. Wide-angle GIXD measurements indicate a contraction of 1-4% in features attributed to polymer crystalline domains upon annealing. Comparison of pre-and post-annealed films reveals increased correlation between polymer scattering features in the latter, consistent with improved ordering of the polymer backbone and sidechains. These findings, together with GIXD measurements of full device stacks and accelerated aging measurements of operational cells, support recent reports on the high photoconversion efficiency stability of this polymer BHJ system for highly scalable, long-lifetime OPVs.

Polymer : fullerene blend films are the best studied materials systems for organic photovoltaic energy conversion. Whilst the variety of donor materials studied is huge, the vast majority of systems use either phenyl-C61 butyric acid methyl ester (PCBM) or its C71 analogues (PC70BM) as the electron acceptor. The choice places a constraint on the donors that may be used and may exclude high oxidation potential donor materials that would otherwise be good candidates for stable photovoltaic devices. Recently, Solenne BV has developed a new ketolactam fullerene (KL) which is a stronger acceptor than PCBM. Here, we study the photocurrent generation and charge generation properties of blend devices of the new fullerene with polymers which have exhibited insufficient driving force for excitons generated in the polymer to separate into free charge carriers, when blended with PCBM or PC70BM. An example is the low LUMO benzotrithiophene-co-diketopyrrolopyrrole polymer, BTT-DPP[1,2]. We compare the external and internal quantum efficiency spectra, current-voltage characteristics and charge generation yield for polymer:PCBM and polymer:KL systems, and thereby identify the factors limiting charge generation in these systems.

Оrganic field-effect transistors (OFET) can combine photodetection and light amplification and, for example, work as phototransistors. Such organic phototransistors can be used in light-controlled switches and amplifiers, detection circuits, and sensors of ultrasensitive images. In this work, we present photophysical characterization of well-defined ultrathin organic field-effect devices with a semiconductive channel based on Langmuir-Blodgett monolayer film. We observe clear generation of photocurrent under illumination with a modulated laser at 405 nm. The increase of photocurrent with the optical modulation frequency indicates the presence of defect states serving as traps for photogenerated carriers and/or the saturation of charge concentration in the thin active layer. We also propose a simple one-dimensional numerical model of a photosensitive OFET. The model is based on the Poisson, current continuity and drift-diffusion equations allows future evaluation of the photocurrent generation mechanism in the studied systems.

Here we investigate light trapping substrates and electrodes for enhancing the performance of organic photovoltaics (OPVs). Their power conversion efficiency (PCE) can be improved by a factor of 1.16 using laser patterned PET substrates and by a factor of 1.13 using commercial, structured display films. Furthermore, we prepare light trapping electrodes using as flexible conductive polymer with embedded TiO₂ nanoparticles, improving the PCE by a factor of 1.08 as compared to a neat polymer electrode. However, nano-imprinted conductive polymer electrodes does not provide light trapping effect due to the small size (50 nm) of the structures. Moreover flexible OPV devices, integrating the above light trapping elements, show non-degraded performance after bending tests.

The role of MAPbI₃ perovskite crystal facet surface property, surface cohesion, was investigated in this study. The interaction energy of as grown MAPbI₃ perovskite crystal facet (002), (110), (112) and (200) with organic PSS-PEDOT, PCBM and Sprio-OMeTAD molecules were obtained using molecular dynamics simulations. The results indicated that these three molecules can interact well with all four common facets of MAPbI₃ crystal producing negative interactive energies. The interacting between Sprio-OMeTAD molecule and the MAPbI₃ perovskite crystal surface is the strongest producing the lowest interactive energy. While PCBM is the weakest and PSS-PEDOT in between. The interaction energies of these three molecules show similar preferential orders, they are (112), (002), (200) and (110) respectively. In the PCBM case, energy differences among facet surfaces (002), (110) and (200) are small when compare with surface (112). Solar cells made from tailored crystals with large (112)/(002) surfaces can be expected to have better crystal-PEDPT:PSS contact therefore, better hole injection efficiency. Same goes to the Sprio-OMeTAD and PCBM where higher electron extraction efficiency can be expected.

In this work we present the results of a study of twenty natural pigments obtained from plants and insects from southern Ecuador. Many of them will be considered as a potential natural sensitizer for the construction of DSSCs. The results indicate that these pigments have a good performance in the absorbance and wavelength spectra. Were selected four best pigments for the construction of DSSCs, Rumex tolimensis Wedd, Raphanus sativus, Hibiscus sabdariffa, and Prunus serótina, however the conversion efficiency is lower than 1%.

Plastic optoelectronic materials and thin film devices are very attractive in future optical sensor and solar energy applications due to their lightweight, flexible shape, high photon absorption coefficients, low cost, and environmental benefits. In this study, optoelectronic properties of D, D/fA blend, DfA, and a series of DBfA type of conjugated block copolymers has been investigated, where D is a donor type PPV conjugated block, B is a non-conjugated and flexible aliphatic hydrocarbon bridge chain containing different number of aliphatic methylene units, and fA is a fluorinated acceptor type PPV conjugated block. The optical absorptions of the D/fA blend, DfA, and DBfAs are typical overlaps of individual absorptions of D and fA blocks, while the solution steady state photoluminescence (PL) emission of D were quenched to different levels in blends and block copolymers, with DBfAs containing one methylene unit bridge (DB₁fA) quenched most. This could be attributed to an intra-molecular photo induced electron transfer or charge separation in DBfA systems. Theoretical first principles study of the equilibrium atomic configuration of DfA reveals the existence of twisting angles between the D and fA blocks in DfA stable states which may account for a less PL quenching of DfA as compared to DB₁fA. These results are important for designing and developing high efficiency polymer based optoelectronic systems.