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Copolymers based on dithieno[3,2-b:2′,3′-d]silole (DTS) and dithienylthiazolo[5,4- d]thiazole (TTz) are synthesized and tested in an all-solution roll process for polymer solar cells (PSCs). Fabrication of polymer:[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) solar cells is done on a previously reported compact coating/printing machine, which enables the preparation of PSCs that are directly scalable with full roll-to-roll processing. The positioning of the side-chains on the thiophene units proves to be very significant in terms of solubility of the polymers and consequently has a major impact on the device yield and process control. The most successful processing is accomplished with the polymer, PDTSTTz-4, that has the side-chains situated in the 4-position on the thiophene units. Inverted PSCs based on PDTSTTz-4 demonstrate high fill factors, up to 59%, even with active layer thicknesses well above 200 nm. Power conversion efficiencies of up to 3.5% can be reached with the roll-coated PDTSTTz-4:PCBM solar cells that, together with good process control and high device yield, designate PDTSTTz-4 as a convincing candidate for high-throughput roll-to-roll production of PSCs. [ABSTRACT FROM AUTHOR]

The role of the common stress factors such as high temperature, humidity, and UV irradiation on interface adhesion of roll-to-roll fabricated organic photovoltaic (OPV) devices is investigated. The samples range from bare front electrodes to complete devices. It is shown that applying single stress or combinations of stresses onto the samples variably affect the adhesion properties of the different interfaces in the OPV device. It is revealed that while the exposure of the complete devices to the stresses results in the loss of photovoltaic performance, some interfaces in the devices present improved adhesion properties. Depth profiling analysis on the fractured samples reveals interdiffusion of layers in the structure, which results in the increase of adhesion and change of the debond path. It is shown that through diffusion and intermixing of internal interfaces coupled stresses can increase the adhesion of OPV interfaces by over tenfold. The results are additionally compared to the photovoltaic performance of the complete devices. [ABSTRACT FROM AUTHOR]

The results of a meta-analysis conducted on organic photovoltaics (OPV) lifetime data reported in the literature is presented through the compilation of an extensive OPV lifetime database based on a large number of articles, followed by analysis of the large body of data. We fully reveal the progress of reported OPV lifetimes. Furthermore, a generic lifetime marker has been defined, which helps with gauging and comparing the performance of different architectures and materials from the perspective of device stability. Based on the analysis, conclusions are drawn on the bottlenecks for stability of device configurations and packaging techniques, as well as the current level of OPV lifetimes reported under different aging conditions. The work is summarized by discussing the development of a tool for OPV lifetime prediction and the development of more stable technologies. An online platform is introduced that will aid the process of generating statistical data on OPV lifetimes and further refinement of the lifetime prediction tool. [ABSTRACT FROM AUTHOR]

The effect of substituting lead with tin in perovskite‐based solar cells (PSCs) has shows that lead is preferred over tin by a lower cumulative energy demand. The results, which also include end‐of‐life management, show that a recycling scenario that carefully handles emission of lead enables use of lead in PSCs with little environmental impact. All other scenarios result in catastrophic emission of lead to the environment that would spell an end to widespread use of lead in PSCs. [ABSTRACT FROM AUTHOR]

A scaling effort on perovskite solar cells is presented where the device manufacture is progressed onto flexible substrates using scalable techniques such as slot-die roll coating under ambient conditions. The printing of the back electrode using both carbon and silver is essential to the scaling effort. Both normal and inverted device geometries are explored and it is found that the formation of the correct morphology for the perovskite layer depends heavily on the surface upon which it is coated and this has significant implications for manufacture. The time it takes to form the desired layer morphology falls in the range of 5-45 min depending on the perovskite precursor, where the former timescale is compatible with mass production and the latter is best suited for laboratory work. A significant loss in solar cell performance of around 50% is found when progressing to using a fully scalable fabrication process, which is comparable to what is observed for other printable solar cell technologies such as polymer solar cells. The power conversion efficiency (PCE) for devices processed using spin coating on indium tin oxide (ITO)-glass with evaporated back electrode yields a PCE of 9.4%. The same device type and active area realized using slot-die coating on flexible ITO-polyethyleneterphthalate (PET) with a printed back electrode gives a PCE of 4.9%. [ABSTRACT FROM AUTHOR]

The results presented demonstrate how the screening of 104 light-absorbing low band gap polymers for suitability in roll coated polymer solar cells can be accomplished through rational synthesis according to a matrix where 8 donor and 13 acceptor units are organized in rows and columns. Synthesis of all the polymers corresponding to all combinations of donor and acceptor units is followed by characterization of all the materials with respect to molecular weight, electrochemical energy levels, band gaps, photochemical stability, carrier mobility, and photovoltaic parameters. The photovoltaic evaluation is carried out with specific reference to scalable manufacture, which includes large area (1 cm2), stable inverted device architecture, an indium-tin-oxide-free fully printed flexible front electrode with ZnO/PEDOT:PSS (poly(3,4-ethylenedioxythiophene):polystyrene sulfonate), and a printed silver comb back electrode structure. The matrix organization enables fast identification of active layer materials according to a weighted merit factor that includes more than simply the power conversion efficiency and is used as a method to identify the lead candidates. Based on several characteristics included in the merit factor, it is found that 13 out of the 104 synthesized polymers outperformed poly(3-hexylthiophene) under the chosen processing conditions and thus can be suitable for further development. [ABSTRACT FROM AUTHOR]

Continuous flow methods are employed for the controlled polymerization of the roll-to-roll (R2R) compatible polymer PBDTTTz-4 including optimization and upscaling experiments. The polymerization rate and materials' quality can be increased significantly with the continuous flow method where reaction times down to 10 min afforded PBDTTTz-4 with high molecular weight and a constant quality. The flow method enables full control of the molecular weight via tuning of the flow speed, catalyst loading, and temperature and avoids variation in materials' quality associated with conventional batch synthesis. Upscaling from 300 mg batch synthesis to 10 g flow synthesis affords PBDTTTz-4 with a production rate of up to 120 g day-1 for a very simple in-house build flow reactor. An average power conversion efficiency (PCE) of 3.5% is achieved on a small scale (1 cm²) and an average PCE of 3.3% is achieved on a large scale (29 cm²). This shows that small device efficiencies can be scaled when using full R2R processing of flexible and encapsulated carbon-based modules without the use of vacuum, indium-tin-oxide, or silver, with the best achieving a PCE of 3.8% PCE. [ABSTRACT FROM AUTHOR]

Continuous flow methods are employed for the controlled polymerization of the roll-to-roll (R2R) compatible polymer PBDTTTz-4 including optimization and upscaling experiments. The polymerization rate and materials' quality can be increased significantly with the continuous flow method where reaction times down to 10 min afforded PBDTTTz-4 with high molecular weight and a constant quality. The flow method enables full control of the molecular weight via tuning of the flow speed, catalyst loading, and temperature and avoids variation in materials' quality associated with conventional batch synthesis. Upscaling from 300 mg batch synthesis to 10 g flow synthesis affords PBDTTTz-4 with a production rate of up to 120 g day−1 for a very simple in-house build flow reactor. An average power conversion efficiency (PCE) of 3.5% is achieved on a small scale (1 cm2) and an average PCE of 3.3% is achieved on a large scale (29 cm2). This shows that small device efficiencies can be scaled when using full R2R processing of flexible and encapsulated carbon-based modules without the use of vacuum, indium-tin-oxide, or silver, with the best achieving a PCE of 3.8% PCE. [ABSTRACT FROM AUTHOR]

The impact of additives mixed with poly(3,4-ethylenedioxythiophene):polysty­renesulfonate (PEDOT:PSS) on the stability of organic photovoltaic modules is investigated for fully ambient roll-to-roll (R2R) processed indium tin oxide free modules. Four different PEDOT:PSS inks from two different suppliers are used. The modules are manufactured directly on barrier foil without a UV filter to accelerate degradation and enable completion of the study in a reasonable time span. The modules are subjected to stability testing following well-established protocols developed by the international summit on organic photovoltaic stability (ISOS). For the harsh indoor test (ISOS-L-3) only a slight difference in stability is observed between the different modules. During both ISOS-L-3 and ISOS-D-3 one new failure mode is observed as a result of tiny air inclusions in the barrier foil and a R2R method is developed to detect and quantify these. During outdoor operation (ISOS-O-1) the use of ethylene glycol (EG) as an additive is found to drastically increase the operational stability of the modules as compared to dimethylsulfoxide (DMSO) and a new failure mode specific to modules with DMSO as the additive is identified. The data are extended in an ongoing experiment where DMSO is used as additive for long-term outdoor testing in a solar park. [ABSTRACT FROM AUTHOR]

The realization of a complete tandem polymer solar cell under ambient conditions using only printing and coating methods on a flexible substrate results in a fully scalable process but also requires accurate control during layer formation to succeed. The serial process where the layers are added one after the other by wet processing leaves plenty of room for error and the process development calls for an analytical technique that enables 3D reconstruction of the layer stack with the possibility to probe thickness, density, and chemistry of the individual layers in the stack. The use of ptychography on a complete 12-layer solar cell stack is presented and it is shown that this technique provides the necessary insight to enable efficient development of inks and processes for the most critical layers in the tandem stack such as the recombination layer where solvent penetration in fully solution processed 12-layer stacks is critical in eleven of the steps. [ABSTRACT FROM AUTHOR]

As mass-produced, low-cost organic electronics enter our everyday lives, so does the waste from them. The challenges associated with end-of-life management must be addressed by careful design and carbon-based electrodes are central to these developments. Here, the reproducible production of vacuum-, indium tin oxide (ITO)-, and silver-free solar cells in a fully packaged form using only roll-to-roll processing is reported. Replacing silver with carbon as electrode material significantly lowers the manufacturing cost and makes the organic photovoltaic (OPV) modules environmentally safe while retaining their flexibility, active area efficiency, and stability. The substitution of silver with carbon does not affect the roll-to-roll manufacturing of the modules and allows for the same fast printing and coating. The use of carbon as electrode material is one step closer to the wide release of low-cost plastic solar cells and opens the door to new possible applications where silver recycling is not manageable. [ABSTRACT FROM AUTHOR]

The tandem concept involves stacking two or more cells with complementary absorption spectra in series or parallel connection, harvesting photons at the highest possible potential. It is strongly suggested that the roll-to-roll production of organic solar cells will employ the tandem concept to enhance the power conversion efficiency (PCE). However, due to the undeveloped deposition techniques, the challenges in ink formulation as well as the lack of commercially available high performance active materials, roll-to-roll fabrication of highly efficient organic tandem solar cells currently presents a major challenge. The reported high PCE values from lab-scale spin-coated devices are, of course, representative, but not helpful for commercialization. Here, organic tandem solar cells with exceptionally high fill factors and PCE values of 7.66% (on glass) and 5.56% (on flexible substrate), which are the highest values for the solution-processed tandem solar cells fabricated by a mass-production compatible coating technique under ambient conditions, are demonstrated. To predict the highest possible performance of tandem solar cells, optical simulation based on experimentally feasible values is performed. A maximum PCE of 21% is theoretically achievable for an organic tandem solar cell based on the optimized bandgaps and achieved fill factors. [ABSTRACT FROM AUTHOR]

Steadily increasing efficiencies of organic solar cells are frequently published but the practical demonstration of actual large-scale installations with high power output has been very limited. Here, the real-world challenges and opportunities of organic solar cells fabricated on thin plastic foil and mounted in solar cell arrays of more than 1 kW are shown. In this configuration defects in form of burns that have never been reported before are observed. The reason can be seen in the combination of high power production, water ingress, and the use of thin plastic foil as the substrate. Environmental impact such as lightning was also observed to cause randomly distributed burn holes that initiate self-sustained damaging under illumination. The large solar cell modules each with more than 220 Wpeak are based only on serially connected cells and need no time-consuming manual wiring of single cells. Although burns that locally destroy the modules are observed the efficiency is not much affected. Simple repair procedures developed throughout the lifetime study enable the cut and replace of small pieces of the module. A complete replacement as it is carried out for malfunctioning conventional Si-based PV modules is not necessary. This enables cost-effective maintenance over the lifetime of the organic solar cells. [ABSTRACT FROM AUTHOR]

Indium-tin-oxide-free (ITO-free) polymer solar cells with composite electrodes containing current-collecting grids and a semitransparent poly(3,4-ethylenedioxythiophene):polystyrenesulfonate) (PEDOT:PSS) conductor are demonstrated. The up-scaling of the length of the solar cell from 1 to 6 cm and the effect of the grid line resistance are explored for a series of devices. Laser-beam-induced current (LBIC) mapping is used for quality control of the devices. A theoretical modeling study is presented that enables the identification of the most rational cell dimension for the grids with different resistances. The performance of ITO-free organic solar cells with different dimensions and different electrode resistances are evaluated for different light intensities. The current generation and electric potential distribution are found to not be uniformly distributed in large-area devices at simulated 1 Sun illumination. The generated current uniformity increases with decreasing light intensities. [ABSTRACT FROM AUTHOR]

Photovoltaic tandem technology has the potential to boost the power conversion efficiency of organic photovoltaic devices. Here, a reliable and efficient fully solution-processed intermediate layer (IML) consisting of ZnO and neutralized poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is demonstrated for series-connected multi-junction organic solar cells (OSCs). Drying at 80 °C in air is sufficient for this solution-processed IML to obtain excellent functionality and reliability, which allow the use of most of high performance donor materials in the tandem structure. An open circuit voltage ( Voc) of 0.56 V is obtained for single-junction OSCs based on a low band-gap polymer, while multi-junction OSCs based on the same absorber material deliver promising fill factor values along with fully additive Voc as the number of junctions increase. Optical and electrical simulations, which are reliable and promising guidelines for the design and investigation of multi-junction OSCs, are discussed. The outcome of optical and electrical simulations is in excellent agreement with the experimental data, indicating the outstanding efficiency and functionality of this solution-processed IML. The demonstration of this efficient, solution-processed IML represents a convenient way for facilitating fabrication of multi-junction OSCs to achieve high power conversion efficiency. [ABSTRACT FROM AUTHOR]

Evaporation is the most commonly used deposition method in the processing of back electrodes in polymer solar cells used in scientific studies. However, vacuum-based methods such as evaporation are uneconomical in the upscaling of polymer solar cells as they are throughput limiting steps in an otherwise fast roll-to-roll production line. In this paper, the applicability of inkjet printing in the ambient processing of back electrodes in inverted polymer solar cells with the structure ITO/ZnO/P3HT:PCBM/PEDOT:PSS/Ag is investigated. Furthermore, the limitation of screen printing, the commonly employed method in the ambient processing of back electrode, is demonstrated and discussed. Both inkjet printing and screen printing of back electrodes are studied for their impact on the photovoltaic properties of the polymer solar cells measured under 1000 Wm−2 AM1.5. Each ambient processing technique is compared with evaporation in the processing of back electrode. Laser beam induced current (LBIC) imaging is used to investigate the impact of the processing techniques on the current collection in the devices. We report that inkjet printing of back electrode delivers devices having photovoltaic performance comparable to devices with evaporated back electrodes. We further confirm that inkjet printing represent an efficient alternative to screen printing. [ABSTRACT FROM AUTHOR]

Concentrated light is used to perform photochemical degradation of polymer solar cell materials with acceleration factors up to 1200. At constant temperature the photon efficiency in regards to photo degradation is constant for 1–150 suns and oxygen diffusion rates are not a limiting factor. Accelerated degradation by concentrated light thus allows for rapid and precise evaluations of one sun polymer stabilities. [ABSTRACT FROM AUTHOR]

Small polymer solar cell modules that are manufactured without indium‐tin‐oxide using only roll‐to‐roll printing and coating techniques under ambient conditions enable facile integration into a simple demonstrator (for example a laser pointer). Semitransparent front electrode grid structures prepared by roll‐to‐roll inkjet printing in conjunction with photonic sintering enable preparation of complete modules on flexible substrates and subsequent integration of the modules into a laser pointer demonstrator. [ABSTRACT FROM AUTHOR]

Indium-tin-oxide (ITO) free polymer solar cells prepared by ink jet printing a composite front electrode comprising silver grid lines and a semitransparent PEDOT:PSS conductor are demonstrated. The effect of grid line density is explored for a large series of devices and a careful modeling study enabling the identification of the most rational grid structure is presented. Both optical and light beam induced current (LBIC) mapping of the devices are used to support the power loss model and to follow the evolution of the performance over time. Current generation is found to be evenly distributed over the active area initially progressing to a larger graduation in areas with different performance. Over time coating defects also become much more apparent in the LBIC images. [ABSTRACT FROM AUTHOR]

In article number 1402186, Eva Bundgaard and co‐workers present a large study via which a library of conjugated polymers is developed to identify lead candidates that are suitable for indium tin oxide (ITO)‐free, flexible polymer solar cells that are fully printed under ambient conditions. Based on several characteristics, 13 lead candidates are found, out of the 104 synthesized polymers. The variation in light absorption (color) of the 104 synthesized polymers is shown on the cover. Cover picture by Markus Hösel. [ABSTRACT FROM AUTHOR]

Jens W. Andreasen and co‐workers identify and surmount the challenges of fast and scalable manufacture of polymer tandem solar cells as reported in article number 1400736. This is accomplished by combining in situ X‐ray scattering and the high resolution 3D X‐ray vision provided by coherent synchrotron radiation diffractive imaging. [ABSTRACT FROM AUTHOR]