Can Laminated Carbon Challenge Gold? Toward Universal, Scalable, and Low-Cost Carbon Electrodes for Perovskite Solar Cells

While perovskite solar cell (PSC) efficiencies are soaring at a laboratory scale, these are most commonly achieved with evaporated gold electrodes, which would present a significant expense in large-scale production. This can be remedied through the use of significantly cheaper carbon electrodes that, in contrast to metals, also do not migrate through the device. To this end, the present work investigates simple-to-prepare aluminum-supported carbon electrodes derived from commercially available, inexpensive materials that can be applied onto various hole-transporting materials and enable photovoltaic performances on par with those provided by gold electrodes. Successful integration of the new carbon-based electrode into flexible devices produced by a roll-to-roll printing technology by both pressing and lamination is demonstrated. However, temperature cycling durability tests reveal that the use of carbon electrodes based on commercial pastes is hindered by incompatibility of adhesive additives with the key components of the PSCs under heating. Resolving this issue, tailor-made graphite electrodes devoid of damaging additives are introduced, which improve the PSC stability under temperature cycling test protocol to the level provided by benchmark gold electrodes. The study highlights current challenges in developing laminated carbon electrodes in PSCs and proposes strategies toward the resolution thereof.This work was funded by the Australian Centre for Advanced Photovoltaics and Australian Renewable Energy Agency. A.N.S. also acknowledges the financial support from the Australian Research Council (Centre of Excellence CE140100012; Future Fellowship FT200100317). Monash Centre for Electron Microscopy (MCEM) and Melbourne Centre for Nano fabrication (MCN) are acknowledged for providing access to their facilities. The authors are grateful to Dr T. Zhang, A. Surmiak, Dr. N. Peris, Dr. D. Senevirathna, and Dr. N. Pai from Monash University for the experimental support throughout this study

Controlling Homogenous Spherulitic Crystallization for high-efficiency Planar Perovskite Solar Cells fabricated under ambient high-humidity conditions

The influence of precursor solution properties, fabrication environment, and antisolvent properties on the microstructural evolution of perovskite films is reported. First, the impact of fabrication environment on the morphology of methyl ammonium lead iodide (MAPbI3) perovskite films with various Lewis‐base additives is reported. Second, the influence of antisolvent properties on perovskite film microstructure is investigated using antisolvents ranging from nonpolar heptane to highly polar water. This study shows an ambient environment that accelerates crystal growth at the expense of nucleation and introduces anisotropies in crystal morphology. The use of antisolvents enhances nucleation but also influences ambient moisture interaction with the precursor solution, resulting in different crystal morphology (shape, size, dispersity) in different antisolvents. Crystal morphology, in turn, dictates film quality. A homogenous spherulitic crystallization results in pinhole‐free films with similar microstructure irrespective of processing environment. This study further demonstrates propyl acetate, an environmentally benign antisolvent, which can induce spherulitic crystallization under ambient environment (52% relative humidity, 25 °C). With this, planar perovskite solar cells with ≈17.78% stabilized power conversion efficiency are achieved. Finally, a simple precipitation test and in situ crystallization imaging under an optical microscope that can enable a facile a priori screening of antisolvents is shown

Machine learning-assisted development of organic photovoltaics via high-throughput in situ formulation

The discovery of high-performance non-fullerene acceptors and ternary blend systems has resulted in a breakthrough in the efficiency of organic photovoltaics (OPVs) and has created new opportunities for commercialization. However, manufacturing technology has remained far behind expectations. Here we show a new research approach to develop OPVs via industrial roll-to-roll (R2R) slot die coating in conjunction with the in situ formulation technique and machine learning (ML) technology. The formulated PM6:Y6:IT-4F ternary blends deposited on continuously moving substrates resulted in the high-throughput fabrication of OPVs with various compositions. The system was used to produce training data for ML prediction. The composition/deposition parameters, referred to as deposition densities, and the efficiencies of 2218 devices were used to screen ML algorithms and to train an ML model based on a Random Forest regression algorithm. The generated model was used to predict high-performance formulations and the prediction was experimentally validated by fabricating 10.2% efficiency devices, the highest efficiency for R2R-processed OPVs so far

A novel spiro-functionalized polyfluorene derivative with solubilizing side chains

We report on a new polyfluorene derivative containing a spiroanthracenefluorene unit with a remote C-10 position that provides facile substitution of alkyl groups. An ethylhexyl group was introduced into the spiroanthracenefluorene unit and the ethylhexyl-substituted spiroanthracenefluorene was polymerized via an Ni(0)-mediated polymerization. The polymer showed a high spectral stability with respect to heat treatment, UV irradiation, and high current passage. A light-emitting device based on this polymer showed an emission in a deep blue region with CIE color coordinates of x= 0.17 and y= 0.12

Water-soluble polyfluorenes as an electron injecting layer in PLEDs for extremely high quantum efficiency

A cationic water-soluble polyfluorene containing ion-transporting side groups and mobile metal ions is synthesized. The material is used as an electron injection layer in polymer light-emitting diodes with high-work-function Al cathodes. The devices show high quantum efficiencies (see figure), with a maximum external quantum efficiency of 4.8%, approaching the theoretical maximum external quantum efficiency of about 5%.N

Organic photovoltaics’ new renaissance: advances toward roll-to-roll manufacturing of non-fullerene acceptor organic photovoltaics

Non-fullerene acceptors (NFAs) have recently breathed new life into organic photovoltaic (OPVs), achieving breakthrough photovoltaic conversion efficiencies. Unlike conventional fullerene acceptors, they offer strong levels of tunability and solution-processibility that allow them to be easily exploited in the roll-to-roll (R2R) fabrication process. This has enabled a new renaissance for OPVs in the face of other photovoltaic material candidates for large-scale, high-throughput, cost-effective manufacturing. In this review, the current progress of R2R manufacturing of NFA-OPVs and the applications enabled by them are summarized. The perspectives on their research, technological, and future prospects for industry scale-up are also presented.Nanyang Technological UniversityPublished versionThis work was supported by the Australian Centre for Advanced Photovoltaics (ACAP) program funded by the Australian Government through the Australian Renewable Energy Agency (ARENA). This work is also supported via funding from the Nanyang Technological University (NTU) College of Engineering International Postdoctoral Fellowship. Prof. Justin M. Hodgkiss acknowledges support from the Marsden Fund of New Zealand

Hot slot die coating for additive-free fabrication of high performance roll-to-roll processed polymer solar cells

Hot solution deposition has emerged as a promising strategy to achieve high performance polymer solar cells and many state-of-the-art devices have been recently fabricated by this approach in research laboratories. Currently, a major challenge in the photovoltaics community is translating such methodologies into industrially relevant processes so that progress can be made beyond the research community. In this work, hot deposition is developed via a slot die coating process, using a thermally robust and thickness tolerant photovoltaic polymer and a 3D printer-based slot die coater. This method uses not only hot substrates but also hot solutions. We find that controlling solution and substrate temperatures is critical to achieve optimum morphology and high device performance. Analysis of nano-morphology and molecular packing shows a clear influence of both solution and substrate temperatures. At optimal temperature conditions (80 degrees C head-80 degrees C substrate), slot die coated devices with an inverted configuration exhibited up to a 7.61% power conversion efficiency without using additives or other processing treatments, which are detrimental to stability and processing efficiency. The optimum temperature combination was readily scaled up using roll-to-roll processing equipment without further optimization, yielding flexible polymer solar cells with a 7.06% power conversion efficiency, demonstrating the potential of the hot slot die coating method from an industrial perspective