In the Chief Executive’s 2020 policy address, Hong Kong SAR government has announced a determined effort towards carbon neutrality before 2050. It becomes urgent to decarbonize the energy system by exploiting solar energy. Because the conventional silicon solar cell technology reaches its plateau, the field is striving for a disruptive solar cell technology that can transform the landscape of solar energy. Perovskite solar cells have thus emerged as a near ideal technology option. In contrast to conventional solar cells, highly efficient perovskite solar cells are fabricated by solution printing in ambient conditions, thus offering an unprecedented opportunity for clean energy generation at extremely low cost. Perovskite solar cells also possess market-attractive flexible and semitransparent features, which will reform our impression on solar panels and create an aesthetically pleasing, carbon-free urban environment. A huge potential impact is being seen for deploying perovskite solar cell to reduce carbon footprint of modern cities like Hong Kong.
The research laboratory of Dr. Yuanyuan (Alvin) Zhou, Assistant Professor in the Department of Physics at HKBU, is doing cutting-edge research on perovskite solar cells. Just earlier this year, Dr. Zhou led an international research collaboration to deliver perovskite solar cells bendable thousands of times, a development promising for build-integrated power-generation applications. Now Dr. Zhou, together with major collaborators from the Brown University and National Renewable Energy Laboratory, have made another important step for bringing this technology to the ideal. They have achieved ideal-band-gap perovskite solar cells that simultaneously demonstrate high efficiency and stability. This work is now published in the latest issue of Matter, the flagship journal in materials science for Cell Press.
In physics, the Shockley-Queisser limit is used for predicting the potential of one semiconductor solar cell with various bandgaps. An ideal band gap for a solar cell to reach its efficiency limit is around 1.35 eV. It is promising that one can easily tune the band gap of perovskite solar cells to the ideal region, but the field has rarely realized ideal-band-gap perovskite solar cells that can exhibit both high efficiency and long-term stability, which is mainly due to the lack of a holistic control over the corresponding perovskite thin film properties.
In this study, Dr. Zhou and his collaborators creatively chose a complex additive phase of SnCl2•3FACl that can tailor the thin film growth of ideal-band-gap perovskite semiconductors. They found that this approach not only enhances the microstructure characteristics and physical properties of ideal-band-gap perovskites, but also relaxes the residue thin-film stress, a ‘hidden’ factor now known critical to the performance ofideal-band-gap perovskite solar cells. As a result, the ideal-band-gap perovskite solar cells in this work show power conversion efficiencies beyond 20% and meanwhile an operational stability over seven hundred hours under accelerated tests.
Dr. Zhou’s laboratory plan to further pushing forward this perovskite semiconductor technology via a fundamental investigation into the microscopic mechanisms. He has recently been invited to express his forward-looking opinions related to this research direction on Joule, the flagship journal in energy forCell Press (impact factor: 29.155). Dr. Zhou further comments that fundamental insights into the atomic-scale microstructures and their evolution will guide us to make new inventions towards ideal perovskite solar cells for green energy generation.
 J. Tong#, J. Gong#, M. Hu, S.K. Yadavalli, Z. Dai, F. Zhang, C. Xiao, J. Hao, M. Yang, M.A. Anderson, E.L. Ratcliff, J.J. Berry, N.P. Padture*, Y. Zhou*, K. Zhu*. High-performance methylammonium-free ideal-band-gap perovskite solar cells. Matter 4, 1365-1376 (2021).
 S. Cai, Y. Zhou*. Visualizing the Invisibles in Perovskites. Joule 3, 2545-2548 (2020).