Perovskite Solar Modules

The impressive advance of halide perovskite semiconductors and their application in prototype solar cells over the past decade has opened a window of opportunity for the technology to enter large area production of photovoltaic modules in the near future. Moving from the laboratory-scale perovskite solar cell (PSC) to a perovskite solar module (PSM) involves scientific and technological developments that encompass various aspects ranging from materials science to device engineering as well as novel characterizations methods and numerical models. In particular, the fabrication methods used for processing small area PSC are not adequate for the fabrication of PSM on an industrially relevant scale (>1m2). This Special Issue highlights the growing interest in the scaling-up of the perovskite technology, which can pave the way to its commercialization. The contributions cover a wide range of aspects, ranging from module interconnection scalable processing of perovskite semiconductor thin films, fabrication of high efficiency and stable charge transport layers, low toxicity processing, perovskite/silicon solar modules, and in-situ monitoring of large area processed perovskite thin films. This special issue on perovskite solar modules encompasses 3 perspectives, 4 review articles, and 7 research articles. The four Reviews discuss the limitations and the potentials of the PSMs and their interlayers. Chenquan Yang et al. (10.1002/solr.202100600) presented a comprehensive review titled “Towards commercialization of efficient and stable perovskite solar modules” where the authors examined the recent signs of progress in both solutions and vacuum-based processes towards the scaling up of the perovskite technology. They also reviewed the charge carrier transport, electrode materials, and their scaling methods for high-efficiency and stable photovoltaic devices. Finally, the current strategies for optimizing the environmental stability of devices are highlighted together with the packaging strategies for reducing lead leakage during operation. The review by N. Tiwari et al. (10.1002/solr.202100700) titled “Advances and Potentials of NiOx Surface Treatments for p-i-n Perovskite Solar Cells” covers p-type NiOx, a very prominent hole transport layer (HTL) for p-i-n PSCs due to the suitable valence band energy, the high transparency, and compatibility with various deposition processes. This contribution revisits approaches of surface modifications based on physical (UV-ozone, oxygen, argon, and/or helium plasma), chemical (interlayer passivation), and doping treatments. The impacts of these surface modifications on the structural and optoelectronic properties of the NiOx are discussed and the implications for the power conversion efficiency (PCE) are revisited. Do-Kyoung Lee et al. (10.1002/solr.202100455) studied the materials and methods used for high-efficiency PSMs, with a focus on the formation of large-area perovskite films which significantly affect the PCE in the review “Materials and Methods for High-Efficiency Perovskite Solar Modules”. The direct comparison between materials helps understand the functions of processing and photovoltaic parameters. The review revisits the role of Precursor, additive, and interface engineering as well as various coating methodologies for PSMs. The authors highlighted how the engineering of uniform, pinhole-free, and high-quality large-area perovskite films can contribute to high-efficiency PSMs and pave the way for commercialization. Yuanhang Cheng et al. (10.1002/solr.202100545) in their review on the “Development and Challenges of Metal Halide Perovskite Solar Modules” discuss the challenges to fabricating large-area high-efficiency PSCs with solution-based and vacuum-based deposition technologies. They also analyze the issues of module stability, potential lead leakage issues, and outdoor field tests. The three perspectives focused on the advantages and limitations of perovskite modules and perovskite/silicon modules. Eli J. Wolf et al. (10.1002/solr.202100239) analyzed the limitation and potential to prevent reverse bias under partial shading in the perspective “Designing Modules to Prevent Reverse Bias Degradation in Perovskite Solar Cells When Partial Shading Occurs”. Indeed, Partial shading is a very common problem in the field operation of panels composed of cells in series. The illuminated PSCs can induce a large reverse bias on the shaded cell to attempt to force current through it. This can generate a fast degradation in the performance of the devices. In their perspective, the authors show that panels composed of perovskite–silicon tandems cells can be protected with fewer bypass diodes than with single-junction PSCs or perovskite CIGS tandems. They also suggest different strategies related to how to be positioning the panels to minimize these effects. Zhichun Yang et al. (10.1002/solr.202100458) in the perspective titled “Recent Progress on Metal Halide Perovskite Solar Minimodules” analyzes the advances of PSCs in terms of design and module structure. The authors give an overview of the commonly used technology for the deposition of charge-transport layers as screen printing and evaporation technologies. They also analyzed the role of the contact between the metal electrode and the perovskite layer in the interconnection channel, the stability of PSMs issue is another important factor. They also discuss how to improve PSM's stability by focusing on the development of intrinsic stable perovskite, interface layer, electrode effective barrier, and encapsulation methods. Michele De Bastiani et al. (10.1002/solr.202100493) presented a perspective work titled “All set for efficient and reliable perovskite/silicon tandem photovoltaic modules?” which revisits the future key issues of the perovskite/silicon tandem photovoltaic modules. The authors also discuss various applications of perovskite PV technology its advantages against shading effect and partial failure. The research articles of the issue cover aspects related to perovskite materials as well as scalable methods to fabricate PSMs. Advances on materials and deposition methods are at the heart of the technological progress of high-efficiency PSMs. About the importance to control the morphology formation of perovskite semiconductor thin films to achieve reproducibility S. Ternes et al. (10.1002/solr.202100353) developed a novel correlative in-situ multichannel imaging technique, in a research paper titled Correlative in situ multi-channel imaging for large-area monitoring of morphology formation in solution-processed perovskite layers. The technique obtains reflectance, photoluminescence intensity, and central photoluminescence emission wavelength images on large areas subsecond resolution, allowing to consistently monitoring solution film drying, perovskite nucleation, and perovskite crystallization. A further aspect of key importance to the industrial scale-up of perovskite photovoltaics by solution-based deposition processes is the toxicity of solvents and materials used in the precursor inks and post processes. The toxicity imposes constraints to costs and manufacturing compliance with worldwide worker safety regulations as discussed in the article of R. Swartwout et al. (10.1002/solr.202100567) titled Predicting Low Toxicity and Scalable Solvent Systems for High-Speed Roll-to-Roll Perovskite Manufacturing. The article shows the example of dimethylformamide (DMF) based inks and the costs associated with the handling of hazardous substances are very significant (estimate of ¢3.7/W). Moreover, the authors show that suitable new ink solvent systems with much lower toxicity can be predicted using a Hansen solubility model. Next to reducing the toxicity of the solvents, the sheer amount of toxic materials used in the fabrication needs to be reduced by advanced processing strategies. In this regard, M. Zendehdel et al. (10.1002/solr.202100637) report a universal coating strategy, combining blade and spin coating to realize low-waste layer-by-layer deposition of 3D and 2D perovskite films on large-area substrates in a paper titled Zero-Waste Scalable Blade-Spin Coating as Universal Approach for Layer-By-Layer Deposition of 3D/2D Perovskite Films in High-Efficiency Perovskite Solar Modules. The process is uniform as wells as reproducible and prototype PSCs with high PCE > 19% and very good thermal stability are demonstrated. Next to the perovskite semiconductor, the adequate choice of suitable charge transport layers is pivotal to extract efficiently the charge carriers from the device and ensure stable operation. R. He (10.1002/solr.202100639) reports in their research article titled ‘ Scalable preparation of high-performance ZnO-SnO2 cascaded electron transport layer for efficient perovskite solar modules’ report a scalable and high-performance double-layer electron transport layer (ETL) for efficient and stable PSMs. This double layer exhibits an energy cascade band alignment that facilitates charge extraction and is deposited using scalable deposition processes (spray pyrolysis and blade coating). Using the double layer ETL, the authors present efficient PSMs with PCE up to 17.8%. The importance of material development for the stability of PSMs is highlighted in the article by D. Bogachuk et al. (10.1002/solr.202100527), titled Perovskite Photovoltaic Devices with Carbon-Based Electrodes Withstanding Reverse-Bias Voltages Up to -9V and Surpassing IEC 61215:2016 International Standar, which covers PSCs and PSMs with carbon-based electrodes that demonstrate excellent resilience against reverse-bias-induced degradation. Importantly, the authors demonstrate for the first time a PSM that passes the IEC 61215:2016 test according to international standards at an accredited module testing laboratory. The application of scalable deposition techniques for the fabrication of PSMs is presented in the work of M. Ernst et al. (10.1002/solr.202100535), titled Multi-Layer Blade Coating Fabrication of Methylammonium-Free Perovskite Photovoltaic Modules with 66 cm2 Active Area, where PSCs and PSMs modules up to an area of 66 cm2 have been fabricated by using a blade-coating technique. The development, supported by a theoretical description of the coating based on the Landau-Levich model, represents one of the first examples for a p-i-n architecture where absorber and transporting layer are deposited with a coating technique suitable for large area deposition. The possibility print all the layers including the top electrode is discussed and presented in the research paper of D. Li et al. (10.1002/solr.202100554) titled Series resistance modulation for large-area fully printable mesoscopic perovskite solar cells. Here the authors investigate the impact of the printed carbon-based electrode on the series resistance for a mesoscopic PSC finding the way to reduce it to almost 30% to its initial value by using several strategies including a different geometrical shape of the cell and adding bus bars. This in turn permits to double the efficiency of the PSC. Finally, we want to express our gratitude to all the authors for their valuable contribution to this special issue. The in-depth and swift evaluation of manuscripts as well as the valuable feedback by the reviewers are highly appreciated. Last but not least, we want to thank the editorial team of Solar RRL and in particular Dr. A. Troeger for the organization, the support, and enthusiasm to help our community in the dissemination of science. Annalisa Bruno is a principal scientist at the Energy Research Institute at Nanyang Technological University (ERI@N). She coordinates a team working on perovskite high-efficiency solar cells and minimodules by industraial compatible methods as thermal evaporation. She is also a tenured scientist at Italian National Agency for New Technologies, Energy, and Sustainable Economic Development (ENEA). Previously, she was a postdoctoral research associate at Imperial College London and she received her B.S., M.S., and Ph.D. degrees in physics from the University of Naples Federico II. Her research interests include perovskite optical and electrical proprieties to their implementation in a variety of optoelectronic devices, mostly solar cells. Aldo Di Carlo received his degree in Physics (with honors) from the University of Rome “La Sapienza” (Italy) in 1991 and his Ph.D. degree from the Technische Universität München (Germany) in 1995. He is currently a Full Professor of Optoelectronics and Nanoelectronics at the University of Rome “Tor Vergata” (Italy) and since 2006, he has also been director of the Centre for Hybrid and Organic Solar Energy (CHOSE). Since September 2019 he is Director of the Institute for Structure of Matter of the National Research council (CNR-ISM). Di Carlo is author/coauthor of more than 500 scientific publications on international journals, 13 patents, and several book chapters. Ulrich W. Paetzold is a tenure-track-professor for next generation photovoltaics at Karlsruhe Institute of Technology (KIT). He was a doctoral student at Forschungszentrum Jülich and received his Ph.D. in physics from RWTH Aachen University, then continued as a postdoc at IMEC in Leuven. Since 2016, he leads his own research team at KIT. His research focusses on the interaction between light and structured matter for the purpose of engineering novel materials and optical concepts for solar energy harvesting. He is particularly interested in perovskite thin-film photovoltaics and perovskite based multijunction photovoltaics.