This PDF file contains the front matter associated with SPIE Proceedings Volume 11474, including the Title Page, Copyright information, and Table of Contents.

Carbon-based organic semiconductors have many advantages, like easy large-area preparation on flexible substrates, large variety of materials, and low cost. Recent estimates have shown that organic solar cells have the lowest CO2 footprint of any energy-generating technology. Despite these advantages, many challenges remain before organic solar cells can achieve broad commercial impact. In this talk, I will present an overview over the key features of solid-state organic solar cells and discuss recent progress in the field, leading to lab efficiencies approaching 20% and module efficiencies exceeding 10%. Furthermore, I will discuss key aspects of mass production and application scenarios.

Double cascading energy level alignment is achieved in bulk heterojunction organic solar cells ensuring efficient carrier splitting and transport. This affords unique advantages in optimizing light absorption, exciton splitting, carrier transport, and charge transfer state energy levels in quaternary blends. Solar cell device power conversion efficiency up to 17.40%, the highest in single layered devices, was achieved. The optimization of the electronic structure and morphology resulted in a simultaneous improvement of the open circuit voltage, short circuit current and fill factor. The proper ancillary donor/acceptor material choice provides useful handles in thin film. Control of the electronic structure and charge transfer state energy level is achieved with the choice of donor and acceptor materials, allowing the manipulation of the hole-transfer rates, carrier transport, and non-radiative recombination losses. A detailed structure-property relationship that best manifests the impo

The power conversion efficiencies (PCE) of polymer solar cells have now both reached over 17% for single-junction and multi-junction devices. However, in order the meet the commercialization requirement, further improvement in device stability and the exploration of niche applications of polymer solar cells are urgently needed. In this talk, I will discuss how to utilize an integrated strategy combining material design, interface engineering and optical management to tackle the efficiency and stability challenges of polymer solar cells. The molecular structures, crystal structures, thin film nanostructures, interface and device structures and their relationship to the overall properties of polymer solar cell will be discussed. I will also highlight how to apply high throughput optical calculation to guide the design of semitransparent and tandem polymer solar cells with state-of-the-art performance.

Organic solar cells (OSCs) based on non-fullerene acceptors can achieve high charge generation yields despite near-zero donor-acceptor energy offsets to drive electron-hole separation. In this talk I will present experimental data to show that free charges in these systems are generated by thermally activated dissociation of interfacial charge-transfer excitons (CTEs) that occurs over hundreds of picoseconds at room temperature, three orders of magnitude slower than comparable fullerene-based systems. Upon free electron-hole encounters at later times, CTEs and emissive excitons are regenerated, thus setting up an equilibrium between excitons, CTEs and free charges. This endothermic charge separation process enables these systems to operate close to quasi-thermodynamic equilibrium conditions with no requirement for energy offsets to drive charge separation and achieve greatly suppressed non-radiative recombination.

Our recent studies have found the unique phenomenon where the dissociation becomes a self-stimulated process occurring at donor:acceptor interfaces in non-fullerene organic solar cells [ITO/ZnO/C60-SAM/PM6:Y6/MoO3/Ag] with the remarkable power-conversion efficiency of 15.6 %. The self-stimulated dissociation was discovered by monitoring the dissociation at D:A (PM6:Y6) interfaces with our magneto-photocurrent measurement. It was observed that, as the excitons are increased, the dissociation at D:A interfaces becomes surprisingly easier, once the non-fullerene Y6 molecules are optically excited. This presents a self-stimulated dissociation where the electron-hole pairs experience an internal stimulation at D:A interfaces to dissociate into free carriers. This presentation will discuss the underlying mechanism of establishing self-stimulated dissociation in non-fullerene organic solar cells towards developing high-efficiency photovoltaics in non-fullerene organic solar cells.

In the past, most organic solar cells (OSCs) employed fullerenes as electron acceptors. Recently, the synthesis of novel non-fullerene acceptors (NFAs) resulted in high power conversion efficiencies (PCE) of 18.2%. The remarkably high VOC in NFA-based OSCs has been achieved by increasing charge transfer energy (CT) via closer matching of acceptor (A) and donor (D) energy levels. Moreover, an increase in CT energy can lead to a new loss pathway resulting from charge recombination to the now energetically favorable D and A triplet exciton (TE) states. Formation of TEs is not only causing a new loss pathway and reduced short-circuit current but can also lead to enhanced degradation of the active layer. We studied the polymer donor PBDB-T and its fluorinated version PM6, and the thiophene-based acceptor molecule ITIC and a novel benzothiadiazole-based acceptor molecule Y6. With low temperature spin-sensitive photoluminescence measurements formation of TEs is studied.

Recently, the efficiencies of nonfullerene organic photovoltaics (OPVs) have surpassed 18%. The realization of these high-efficiency OPVs is based on the use of push-pull type conjugated polymer donors, which are costly and not scalable. In contrast, polythiophenes (PTs) hold great promises in cost and scalability, rendering them alternatives to the push-pull type donors for commercial applications. Here, we reveal the crucial role of miscibility and crystallinity in determining the performance of PT:nonfullerene systems. Our study underscores the need for nonfullerene acceptors with much lower miscibility in matching PTs and provides design rules for higher efficiency PT:nonfullerene solar cells.

The development of Non-Fullerene Acceptors (NFAs) for Organic Photovoltaics (OPV) has pushed the device power conversion efficiency over 15%. However, the commercialisation of OPV modules by the roll-to-roll industries requires the processing of thick active-layer films (150-300 nm) and therefore materials with high charge carrier mobilities. The anisotropy and bidimensionality of the NFAs conjugated structure are critical to their solid-state organisation, which in turn affects their electronic functions (e.g. carrier mobility). With our work, we show first insights into the crystallisation of a series of ten commonly used NFAs and its effect on the charge transport, identifying how the structural design of the NFAs facilitates their organisational motifs in the solid-state and exploring the importance of the crystal packing and topological connectivity on the charge transport.

Two-dimensional halide perovskites are exciting new semiconductors that show great promising in low cost and high performance optoelectronics devices. However, the weak chemical bonding of halide perovskites makes them chemically, thermally, and mechanically unstable. To address this critical issue and move forward for commercialization, deeper fundamental insights regarding the degradation mechanism and better stabilization strategies have to be achieved. In this talk, I will present a new molecular approach to the synthesis of high-quality organic-inorganic hybrid perovskite quantum wells through incorporating widely tunable organic semiconducting building blocks as the surface capping ligands. Then, I will talk about the applications of these materials in high performance and highly stable solar cells and thermoelectric conversion devices.

The individual and combined effects of extrinsic (humidity and oxygen) and intrinsic (light, bias, and temperature) stressors on halide perovskite materials by implementing complementary optical and electrical characterization methods. These experiments are critical to assess the stability of the large variety of perovskite materials available for light-absorbing and -emitting applications. To pursue optimal ‘rest’ and ‘recovery’ conditions for device stable operation, we propose the implementation of a machine learning approach based on supervised learning upon exposing the samples to distinct values of humidity, oxygen, illumination, bias, and temperature, which will be discussed in details.

The fundamental gap of hybrid lead halide perovskites decreases linearly with decreasing temperature at ambient conditions. Using MAPbI3 (MA, methylammonium) as example, I will show that this atypical gap renormalization with temperature is due to an equal footing of thermal expansion and electron-phonon interaction effects. I will also present recent results obtained for FAxMA1-xPbI3 solid solutions (FA, formamidinium). Strikingly, the temperature dependence of the gap of a phase stable at intermediate compositions and below ca. 250 K exhibits a quadratic bowing with temperature. Band-structure and lattice-dynamics calculations provide crucial insights into this intriguing temperature behavior of the gap.

An unsolved problem of mixed halide perovskites is the light induced compositional instability. Under illumination microscopic clusters with a higher iodide content form which act as efficient recombination centers reducing device performance. In photoluminescence measurements this leads to the development of a secondary peak at low energies that increases in intensity and shifts towards lower energies. Different theories for about the origin have been developed but the underlying key mechanisms are still under debate. In the presented study the photoluminescence evolution of MAPb(I_1.5Br_1.5) perovskites with varying microstructure is investigated at various excitation densities and temperatures. We find a more evolved segregation mechanism with an intermediate stage between the commonly reported mixed phase and the appearance of the I-rich clusters (Br content < 50%). In this intermediate stage perovskite domains with nearly pure iodide content form (Br content < 25%). Using low excitation densities, the interplay between the I-rich domains and the I-rich clusters leads to a blue shift of the conjunct I-rich luminescence peak. At high excitation densities the I-rich domains and the I-rich clusters are clearly distinguishable, due to a stronger PL response of the I-rich domains. With continuous illumination more I-rich cluster form acting as carrier traps and recombination centers. Due to this, the influence of the few I-rich domains on the PL signature decreases leaving only the commonly reported red shift of the I-rich clusters at later stages of the segregation. The formation of the I-rich domains is fully reversible in the dark and occurs also at elevated temperatures. Measurements on sample with varying grain size further indicate an enhanced formation of those I-rich domains on samples with high grain boundary density possibly by a faster halide mobility along them.

Wide-bandgap the organo-metal halide perovskite solar cells (PSCs) are key for high performance perovskite-based tandem photovoltaics. One key aspect limiting the overall power conversion efficiency (PCE) in the 4-terminal tandem architecture is the imperfect transmission of the incident light below the bandgap of top PSCs. Here, we present periodic and disordered nanostructured ITO electrodes as new strategies to reduce reflection losses and transmission of PSCs. Using the nanostructured ITO, the short-circuit current-density is improved compared to planar references and as a result, an increase in the overall PCE of the solar cells is achieved.

The extraction of charge from perovskite solar cells requires charge diffusion to a charge extraction layer (e.g. PEDOT:PSS), followed by charge extraction. We present a method based on time-resolved luminescence to measure charge diffusion and extraction. We find that hole transfer from methylammonium lead iodide (MAPI) to PEDOT:PSS limits the hole extraction rate, and that faster extraction is obtained by using NiO as a hole extraction layer. In addition we observe a very high hole diffusion coefficient of 2.2 cm2/s in a solution-processed MAPI film that is independent of charge density, suggesting a band-like regime of hole transport.

Our approaches toward efficient lead and lead-free perovskite solar cells are i) development of highly-purified perovskite precursor materials, ii) Development of solution process fabrication methods for the perovskite layer, and iii) Development of organic semiconductors for efficient charge-collection layers. We have synthesized lead-halide and tin halide complexes as purified precursors for perovskite materials, which were later commercialized by TCI and are now widely used in this field as standard precursor materials. We also focus on the intermediates formed during the film-growth and have developed efficient fabrication methods based on the formation mechanism. We have designed and synthesized novel pi-conjugated materials designed to control frontier orbital energy levels, molecular aggregation properties, and the interface with the perovskite layer. In this talk, our recent progress on tin halide perovskite solar cells as well as lead halide perovskites will be introduced.

Spin-coated perovskite solar cells (PSC) have demonstrated an exceptional increase in power conversion efficiencies (PCEs) on small-area devices. Scaling-up this technology requires developing a scalable solution processing techniques like digital inkjet printing that additionally offers maskless free-form depositing. Here, we demonstrate a processing route for an inkjet-printed (IJP) triple cation PSC, which can surpass the 20% PCE limit by optimizing a vacuum crystallization technique that enables absorber layers thicker than 1 micron with a grain boundary-free columnar crystal structure. Further, we replace the vacuum-deposited charge-transport layers with IJP pendants to achieve a PSC layer stack consisting of only IJP functional layers.

Organic photovoltaics (OPVs) are an emerging technology for providing renewable energy. However, translation from lab scale to low cost roll-to-roll manufacturing of OPVs on a commercial scale requires significant research. This presentation will highlight work to overcome challenges such as the use of non-halogenated solvents for reduced toxicity formulations, all-solution processed OPVs, and reduced processing temperatures for compatibility with flexible plastic substrates in roll-to-roll coating. The use of ZnO nanoparticle electron transport layers will be discussed as a method for generating uniform films with sufficiently low work functions (< 3.7eV) for generating high performing OPVs using low temperatures that do not deform plastic substrates and enable roll-to-roll coating. Combining these advances, pilot scale OPV modules were fabricated, reaching 6.3% power conversion efficiency.

Certified efficiency of halogenated Pb-perovskite solar cells has reached 25.2 %. Because of the Pb usage restriction, researches on Pb free perovskite solar cells have been focused on. Halogenated Sn-perovskite is one of candidates for the Pb-free perovskite solar cells. In spite of the similarities of the electronic properties between Pb-perovskite and Sn-perovskite, the efficiency of the Sn-perovskite solar cell was still about 10%, which is far below that of Pb-perovskite solar cells. We report Ge ion doped Sn-perovskite solar cells (Pb free) with 13% efficiency by optimizing A site cations in ASnI3 composition and surface passivation.

Quantum dots (QDs) have extraordinary strong light absorption and size tunable bandgap. However, QD films are typically limited to ~200-300 nm due to their poor charge mobility. This severely limits the quantum efficiency of QD devices for λ <750 nm (infrared). Herein, we report a record 1 μm thick QD film using intercalated graphene layers as transparent current extractors. This overcomes QD poor mobility, ensuring both effective light absorption and charge extraction towards the near-infrared reaching quantum efficiency (EQE) of 90%. The short diffusion length (LD<200 nm) of QDs limits their useful thickness to ~200-300 nm1–4 , resulting in poor infrared light absorption. To overcome this limitation, we have built a 1 µm thick QD film with intercalated transparent graphene electrodes that keep high charge collection efficiency. As a result, the 1 µm intercalated devices show a superior EQE reaching 90% at λ ~800 nm without the drop of quantum efficiency at λ ~700 nm observed in most QD devices. The EQE of intercalated devices improves over the entire λ~ 600-1100 nm spectrum as the thickness increases from 100 nm to 1 μm, clearly breaking the restriction that the diffusion length of QDs imposes on the film thickness. This improves absorption and charge collection in the infrared.

Heterostructure comprising two different materials offer an extra degree of freedom to control absorption band and energy level for more efficient optoelectronic devices. Nevertheless, building the efficient charge transport platform is challenging because of the different physical and chemical nature of those. Colloidal quantum dots (CQDs) and polymer hybrid structures have steadily been studied as well, however, the rational strategy to efficiently extract charge have not been proposed so far; only exhibiting a power conversion efficiency (PCE) of 6 ~ 7 %. Here, we propose a new hybrid architecture that synergistically exploits the benefits of CQDs and organics in photovoltaics by introducing small molecules into a CQD/organic stacked structure. The small molecular bridge, mixed in polymer regime facilitates exciton dissociation and charge transfer to the CQDs layer, leading the high PCE of 13.1%.

OPVs are uniquely suited for applications that include low-cost semitransparent solar cells for building and greenhouse integration. For successful implementation in these applications, there is a need for high-performance transparent electrodes for both the anode and cathode. Furthermore, removing the need for the commonly used ITO will allow for improved device flexibility and lower cost. This work accomplishes this by utilizing AgNWs as both the cathode and anode to make fully solution-processed flexible ST-OPVs. Here, we describe the device design and processing approach to achieve performance comparable to transparent electrodes based on ITO and metal films.

The organic-inorganic hybrid perovskite solar cells have achieved power conversion efficiency on par with that of commercial silicon solar cells. The main challenge towards commercial application is its instability. Quasi-2D perovskite has higher stability and easier tunability compared to 3D perovskite. Tuning the phase distribution according to device architecture is of importance. To better understand the structure-function relationship of perovskite materials, we utilize femtosecond laser spectroscopy to study photophysics of different structures. For example, we manipulate the phase purity and vertical distribution of quasi-2D perovskite, verified by femtosecond transient absorption spectroscopy. We find that solar cell performance is more sensitive to phase purity than vertical phase distribution. In another example, to improve both efficiency and stability simultaneously, a small amount of hydrophobic cation of large size is added into 3D perovskite. We find that the propylammonium is the most effective by comparing a family of different cations. The cations of large size preferentially segregate at the grain boundaries and surface, verified by transient absorption and reflection spectroscopy. Such passivation enhances device efficiency up to 20.1% and improves both device and precursor stabilities.

The methylammonium lead iodide CH₃NH₃PbI₃ (MAPbI₃) perovskites have attracted a lot of attention as a possible absorber material for thin film solar cells due to their bandgap energy, high optical absorption coefficients and low-cost solution-processing deposition approaches. MAPbI₃ perovskite solar cells have evolved with transformative potential with laboratory efficiencies greater than 20%. Perovskite absorber materials are very inexpensive to synthesize and simple to manufacture, making them an extremely commercially viable option. Perovskites of compositional variations ABX₃ can yield a range of crystal structures, phases and stabilities. The Goldschmidt’s Tolerance Factor is a reliable figure of merit or empirical index to forecast the formation of preferred and stable structures and phases with ABX₃ mixed halide perovskite tolerance factors in the range of 0.9 to 1. Here, we probe perovskites of compositional variations ABX₃ with tolerance factors in the range of 0.9 to 1.0, and a large effective ionic radius greater than 200 pm. We report on the structural and optical properties of these perovskites. Photovoltaic (PV) devices were fabricated using these high tolerance factor perovskites. We report we have achieved power conversion efficiencies (PCEs) greater than 21% using the high tolerance factor perovskites investigated. The high tolerance perovskites were also characterized using synchrotron X-ray absorption near edge structure (XANES) spectroscopy at the National Synchrotron Light Source (NSLS) II at Brookhaven National Laboratory (BNL). XANES was used to probe the electronic structure of the high tolerance factor perovskites investigated.

Nowadays, solar industry becomes the fastest growing industry due to the rising demands to solve energy crisis and environmental problems. Third generation solar cells such as organic and perovskite solar cells are all relying on a semiconducting thin-film active layer to harvest the solar energy. The morphology of the active layer in terms of crystal structure, grain size and nanophase separation behavior is known to be critical to the solar cell device performance. Here, we are going to present our recent work on the active layer morphology and its correlations with device performances for several different types of photovoltaic systems. State-of-art synchrotron-based X-ray scattering techniques are employed for the morphology characterization: grazing incidence wide-angle X-ray scattering (GIWAXS) for Angstrom-scale ordering and grazing incidence small-angle X-ray scattering (GISAXS) for nano-scale ordering.

Ruddlesden-Popper layered perovskites have emerged as a promising solution for overcoming the moisture instability of three-dimensional hybrid perovskite materials. Given that the optoelectronic properties of these layered perovskites strongly depend on the dimensionality (n) of the phases present, understanding of the microstructure and order in such materials is important. Typically, the dimensionality of phases present is inferred from optical measurements rather than diffraction measurements which are a more direct probe of structural order. Here we use a combination of grazing-incidence transmission wide-angle X-ray scattering and transmission wide-angle X-ray scattering techniques to probe the in-plane microstructure of highly textured Ruddlesden-Popper films. Our analysis reveals that only diffraction peaks corresponding to n = 1, 2, 3 and ∞ phases are observed due to increasing disorder with increasing n. Evidence for stacking faults from X-ray measurements is also shown.

Photon management of perovskite solar cells (PSCs) is studied by the use of nanohole front contact, which allows improving the JSC of the PSC by providing an improved light incoupling. The front contact integrated with spherical nanocone shaped holes represent a refractive index grating allowing for light incoupling approaching unity while minimizing reflection losses. Besides, the front contact has a comparable refractive index (n~2.5) with the perovskite absorber, which minimizes the front reflections in PSC. Optics and optimization of front contact and solar cell are investigated by three-dimensional (3D) finite-difference time-domain (FDTD) simulations whereas finite element method simulations are used to study the electrical response of the device. Investigations reveal a maximum light incoupling enhancement of 10~12% for the optimized PSC, leading to 10 to 27% JSC enhancement with respect to the planar reference PSC.

Thermal transition of OSCs constituent materials are often insufficiently researched, resulting in trial-and-error rather than rational approaches to post-casting processing strategies to improve aggregation to enhance the power conversion efficiency. Despite the potential utility, little is known about the thermal transitions of the high-performance acceptors. Here, by using an optical method, we discover that the acceptor N3 has a clear solid-state aggregation transition at 82 °C. The transition informs and enables a double-annealing method that can fine‐tune aggregation and the device morphology. Compared with 16.6% efficiency for the control devices, higher efficiency of 17.6% is obtained through the improved protocol. Design of high-performance acceptors with yet lower aggregation transitions might be required to successfully transition to low thermal budget industrial processing methods where annealing temperatures on plastic substrates have to be kept low.

The world of organic solar cells (OSC) have been taken by storm by the recent developments in non-fullerene acceptors (NFAs) with record efficiencies being published in close succession. However, not all polymers that previously performed well in fullerene based devices are suitable for use in a blend with NFAs. This seems to be especially the case for diketopyrrolopyrrole (DPP) based polymers and currently there is a lack of understanding as to why. In our research we aim to improve on solar cell performance of DPP-NFA blends and elucidate the reason behind their suboptimal performance in order to extend the range of useful polymers in high efficiency (near infra-red absorbing) NFA OSCs. Preliminary results look promising with over 50% EQE improvement using a ternary solvent system which we currently attribute to better packing in the IEICO-4F phase.

We report the synthesis of composite interlayers by using alcohol-soluble polyfluorene-wrapped single-walled carbon nanotubes (ASP-wrapped SWNTs) and their application to the electron transport layer in efficient organic solar cells. The ASP enable the individual dispersion of SWNTs in solution. Impressively, ASP-wrapped SWNTs solutions are stable for 54 days, indicating very high dispersion stability. Using the ASP-wrapped SWNTs as a cathode interlayer on zinc oxide nanoparticles (ZnO NPs), 9.45% of power conversion efficiency (PCE) can be obtained in PTB7-th:PC71BM-based organic solar cells, which is mainly attributed to the improvement of the short circuit current. Performance enhancements of 18% and 17% were achieved compared to those of pure ZnO NPs and ASP on ZnO NPs, respectively. The improvement of solar cell performance originates from an increased internal quantum efficiency, balanced mobility between electrons and holes, and minimization of charge recombination.

In this work, we show that it is possible to identify combinations of materials which provide the greatest potential as tandem junctions, and to identify specific combinations of materials and film thicknesses which lead to optimal performance. Using this approach, we have investigated a series of wide-band gap, high open circuit voltage (VOC) photovoltaic polymers as front cells in tandem devices. Using the techniques we have developed, we match these polymers with complimentary low-band gap polymers and rapidly optimize tandem devices. In this way, we have been able to demonstrate tandem devices with PCE of up to 12.8% with a minimal consumption of valuable photoactive materials in tandem device optimization.

Perovskite solar cells have been under the spotlight of the photovoltaics community. However, little is known on the impact of structuring the active material using photonic crystal layers. We present here numerical simulations showing the effect of photonic crystal structuring on the integrated quantum efficiency of perovskite solar cells. The photo-active layer is structured using opal-like perovskite layers made of perovskite (full or truncated) spheres, including hybrid uniform/structured layers, embedded in a TiO₂ matrix. The excitation of quasi-guided modes inside the absorbing spheres increases the integrated quantum efficiency and the photonic enhancement factor. A genetic algorithm approach allows us to determine the optimum structure among more than 1.4 10^9 potential combinations. These numerical results of the benefits of photonic structuring on perovskite solar cells are also compared to experimental studies on selected configurations of perovskite solar cells.

Interfaces between organic electron-donating (D) and electron-accepting (A) materials can show efficient free charge carrier generation upon illumination, enabling organic photovoltaic devices and photodetectors with photon to electron conversion yields approaching 100%. Recently, organic light-emitting diodes (OLEDs) based on charge transfer (CT) (or exciplex) emission occurring at such D-A interfaces have been shown to exhibit high electroluminescence external quantum yields (EQEEL). However, no organic D-A combination with both a high EQEEL, as well as a high free carrier generation yield has been discovered so far. Such a system would result in significantly higher operating voltages in organic solar cells, reduced dark current in organic photodetectors, and reduced driving voltages for OLEDs.

In this research, we focus on the PEDOT:PSS materials, which is widely utilized in the field of organic electronics. First, we applied customized transfer of PEDOT:PSS to inter-layer in planer-type perovskite photovoltaics. The transfer-printed PEDOT:PSS layer led to the favorable crystallinity of perovskite Especially, the better stability resulted from the preserved crystallinity, and the inhibition of the ITO degradation. Second, we fabricated a pH-controlled PEDOT:PSS adjusted by imidazole. The neutral PEDOT:PSS revealed superior and very consistent performance for various active area sizes due to the uniformity of the perovskite crystals. The stability also was enhanced by preventing degradation by strong acid. Finally, a hybrid of PEDOT:PSS and copper chalcogenide nanoparticles (NPs) was used for organic photodiode. Since the NPs formed energy barrier in PEDOT:PSS, the dark current of the device was remarkably suppressed, with excellent detectivity.

Tandem structure provides a practical way to realize high efficiency organic photovoltaic (OPV) cells due to the limited optical absorption in organic semiconductors and tandem cells can be used to extend the wavelength coverage of the solar spectrum for light harvesting. The interconnecting layer (ICL) between subcells in a tandem solar cell plays a critical role in the reproducibility and the performance of tandem devices, and the processability of the ICL in a tandem cell has been a challenge. In this work we report on the fabrication of highly reproducible high efficiency tandem cells by employing a commercially available material, PEDOT:PSS HTL Solar (HSolar), as the hole transporting material used for the ICL. Comparing with the conventional PEDOT:PSS Al 4083, HSolar offers a better wettability on the underlying non-fullerene photoactive layers, resulting in better charge extraction properties of the ICL. When FTAZ:IT-M and PTB7-Th:IEICO-4F are used as the front cell and the back cells to fabricate the tandem solar cells, a power conversion efficiency (PCE) of 14.7% is achieved. To validate the processability of these tandem cells, three other research groups have successfully fabricated tandem cells using the same recipe and the highest PCE obtained is 16.1%. With further development of donor polymers and device optimization, our device simulation results show that a PCE < 22% can be realized in tandem cells in the near future.

The AzRISE-TEP Solar Test Yard is a 600-module capacity test bed that provides the environment for in-situ testing of PV module performance, with real-time data collection of module power production and local weather conditions. This work involves the examination of flexible, semi-transparent, organic photovoltaic (OPV) modules in an outdoor testing environment to study degradation in the hot, arid, Tucson, AZ climate. The work reports on changes in the I-V performance and efficiency of a string of two OPV modules in order to estimate degradation experienced by the OPV modules. The study finds that the module string under test dropped to below 80% of its initial power conversion efficiency (PCE) after 54.58 days, and predicts that the PCE will drop below 50% of its initial state after 114.53 days from deployment.

The inverted organic solar cell devices (iOSCs) were fabricated with different weight ratios 1:0.6, 1:0.8, and 1:1 of P3HT and PCBM, respectively. The photo-physical properties of these devices with varying weight ratios are investigated. We find that the absorption spectra revealed a decrease in the intensities with increasing the fullerene ratio and the peaks were blue shifted. Thin films morphology is evaluated by atomic force microscopy (AFM). The PL quenching suggests that the transfer of photo-induced electrons from P3HT to PCBM increases hugely with an increase in the amount of PCBM. Raman spectroscopy for devices shows a strong reduction in the crystallinity by increasing the ratio of fullerene within the blend. The J-V measurements for all devices were performed under the illumination of simulated AM 1.5 sunlight at 100 mW/cm2. External quantum efficiency (EQE) and Internal quantum efficiency (IQE) measurements are also performed for the best device. The best performance was recorded for the device with 1:1 weight ratio of P3HT and PCBM give Power Conversion Efficiency (PCE) of 3.67%, in contrast to 3.36% for (1:0.8) and 2.51% for 1:0.6 devices.

Perovskites have quickly become globally renowned for their extremely attractive electronic and optical characteristics. However, a clear relationship between the composition and photoelectronic properties of perovskites is still not well understood, developing this understanding is imperative to designing perovskite devices tailored to suit the needs of the application. In this study we characterize chlorine-doped MAPbI thin films produced by aerosol assisted chemical vapor deposition and compare the composition of the sample series via a comprehensive set of spectroscopy techniques including: Raman, photoluminescence, X-ray photoelectron and ultrafast transient absorption spectroscopy. We discuss the spectral properties revealed and relate our findings to the mechanisms attributed to the impressive optoelectronic properties exhibited by the perovskite structure.

In this work, the authors investigate the ferroelectric properties of methylammonium lead iodide, which is the reference material for modern perovskite solar cells. By usage of a particular device architecture of a Si-substrate with microstructured gold electrodes, poling fields are applied to the thin films in lateral direction. Piezoresponse Force Microscopy reveals poling of ferroelectric domains on the nanometer scale, which in turn results in a change of macroscopic conductivity. The electric field that is required to trigger the poling process is of a similar magnitude as electric fields in a solar cell under operation, which underlines the importance of understanding the relationship between microsctructure and solar cell performance.

Organic solar cells based on D18:Y6 recently exhibited a record power conversion efficiency of over 18%. We have initially studied the molecular packing and thermodynamic properties of three D18:NFA blends by employing synchrotron X-ray techniques, secondary ion mass spectrometry and UV-vis miscibility measurements. The D18 polymer exhibits strong chain extension in films, which is beneficial to charge transport. Miscibility and other characterizations explain the disparate performance of three systems and the processing procedures. Our contribution reveals several unique property–performance relations of D18-based photovoltaic devices and help guide design or fabrication of yet higher efficiency organic solar cells.

In this contribution, we use the electron spin as a probe to gain insight into the mechanism of molecular doping in a p-doped zinc phthalocyanine host across a broad range of temperatures (80-280K) and doping concentrations (0-5wt%). Electron paramagnetic resonance (EPR) spectroscopy discloses the presence of two paramagnetic species distinguished by two different g-tensors, which are assigned to a positive polaron on the host and a radical anion on the dopant based on DFT calculations. Combined with modelling, the inspection of the EPR spectra shows that anions on the dopants couple in an antiferromagnetic manner at high doping concentrations and that polarons on the host move with an activation energy much smaller than that inferred from electrical conductivity measurements. We rationalize this difference in terms of the disorder-free, intra-grain motion of the polarons probed by EPR, compared to disorder-limited, inter-grain transport probed via electrical measurements.

Although many efforts have been made to achieve a uniform perovskite film, the use of CH3NH3I:PbI2:DMSO (1:1:1) has been limited. This is because the intermediate phase and crystal phase can coexist in the precursor solution.[1] To solve this, a complex process was inevitably needed to ensure the uniformity.[2] Here, the quality of CH3NH3PbI3 film is simply improved via controlling nonstoichiometric molar ratio.[3] The uniform and dense perovskite layer was successfully fabricated by controlling the perovskite adduct formation. This demonstrated a critical point to improve current density and power conversion efficiency in perovskite photovoltaics. The synergistic effect of morphology and electrical properties has proved the optimized solubility for generating high current densities in inverted perovskite solar cells [1] L. Xie et al., Phys. Chem. Chem. Phys., 2017, 19, 1143 [2] K. Fu et al., Nanoscale, 2016, 8 4181 [3] B. G. Kim et al., Sol. Energy Mater. Sol. Cells, 2019, 192, 24

Porous organic polymers (POP) materials are two and three-dimensional structures formed through covalent bonds and lead to effective charge extraction through large contact areas [1,2]. In this study, by adjusting the synthetic strategy for porous organic polymers (T-POP), soluble, hypertonic and crosslinked polymers with alkyl-modified perylene motifs were produced [3]. As the surface area of this polymer expands, the frequency of contact of molecules between optically active units, such as the perylene motifs of the framework, increases, and π-π stacking becomes stronger. Facilitated charge carrier transport in inverted perovskite solar cells. The T-POP interlayer improves the morphology of the surface on the PC70BM layer to induce smooth current flow and builds an electron carrier pathway by stacking a three-dimensional vertical structure. As a result, the stability of the device was increased by T-POP, and the power conversion efficiency of the applied device was increased by 13%.

In this study, we developed a effective processing protocol to modify the electrical conductivity of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films via post-treatment with an alcohol-based solvent, 2-chloroethanol (2-CE), and to improve their performance as a transparent anode in organic photovoltaics (OPVs). Due to its appropriate boiling point, 2-CE is advantageous both for treating as a liquid phase chemical and for drying from the films via evaporation. We compared the optical and electrical properties of the 2-CE-treated PEDOT:PSS with those of standard 5 vol% dimethyl sulfoxide (DMSO) added PEDOT:PSS. With a similar thickness and transmittance in the visible region, the 2-CE-treated polymer electrodes surpassed the DMSO-added films with regard to the electrical conductivity. Additionally, we conducted X-ray Photoelectron Spectrometer (XPS), Ultraviolet Photoelectron Spectroscopy (UPS), J-V characteristic, Photoluminescence (PL), Impedance spectroscopy.

Metallic glasses are alloys without long-range atomic arrangement, obtained from the atomic structure of its liquid state. The solid metallic glass is fabricated by rapidly quenching the liquid-state alloy, which allows it to circumvent crystal growth prior to solidification. The unique, metallic and amorphous properties of metallic glasses have opened up possibilities for various applications, for they exhibit superior mechanical and chemical stability than that of the conventional crystalline metals. In this research, metallic glass thin film sputtered onto polymeric film exhibited encouraging results in mechanical reversibility through bending tests. Subsequently, suitable sheet resistance and work functions for applications photovoltaic cells were attained through compositional tuning, which enabled fabrication of an electrode for OPV, with enhanced chemical stability than that of crystalline metal.

This paper proposes a new, robust and generic tool to investigate both the series and the shunt resistances, (parasitic resistances), as well as the ideality factor for new generations of solar cells. Focus is given to both dye-sensitized solar cells and perovskite solar cells, where the mesoporous TiO2 layer plays a significant role. A comprehensive study for the mesostructured-based solar cells with respect to conventional solar cells has been conducted regarding the parasitic resistance variation, the effect of the active material and technology on the ideality factor. Experimental data show acceptable agreement with data extracted from the proposed model where the targeted parameters have been estimated.

Different additive materials have been extensively investigated in hybrid perovskite solar cells (PSC) to enhance the crystal growth, minimize defects and to improve the device stability. However, most of the additive engineering attempts are basically dedicated to the improvement of open circuit voltage (Voc) in PSC. There are very few investigations where PSC’s short circuit current density (Jsc) is significantly improved along with the Voc. In this work, a novel organic additive material called Phenylhydrazinium iodide (PHI) has been employed to enhance the Jsc hence the overall power conversion efficiency (PCE) of CH3NH3PbI3 PSC. Surprisingly, after PHI treatment Jsc jumps from around 20 to 23 mA/cm2 which corresponds to ~15% increase of short circuit current density resulting overall 21% improvement in PCE. PHI treatment in wide-bandgap perovskite will help to mitigate the problem of shorter Jsc in compared to low-bandgap perovskite materials in multi-junctional tandem solar cell.