Perovskite solar cells, as an emerging clean energy source, have injected new momentum into the high-quality development of the photovoltaic industry. Recently, Peking University, in collaboration with multiple research groups at home and abroad, proposed a new strategy for improving the performance of perovskite solar cells through coherent growth of high Miller index crystal faces. The relevant research results were published in Nature. This research will provide new growth points for optimizing the performance of perovskite solar cells and is also a fundamental innovation in the field of perovskite photovoltaics Gong Qihuang, an academician of the CAS Member and president of Peking University, told reporters. The "dual path" improves the photoelectric conversion efficiency. The photoelectric conversion efficiency is a measure of the efficiency of solar cells in converting light energy into electrical energy. There are two main ways to improve the photoelectric conversion efficiency of perovskite solar cells: one is to increase the capture rate of incident photon energy by light absorbing materials, that is, to increase the effective absorption of solar energy; The second is to weaken the non radiative recombination of photo generated carriers, that is, to reduce the loss of generated electrical energy inside the battery. For over a decade, a significant amount of research in the field of perovskite solar cells has focused on reducing the loss of electrical energy within the cell. This is achieved by reducing defects at the interfaces of the perovskite absorber layer and various functional layers, thereby reducing the non radiative recombination energy loss of photo generated carriers within the cell. This approach of "reducing defects and improving efficiency" has achieved good results, and the relevant understanding has become increasingly sophisticated. The Peking University team has been conducting long-term research on defect control and performance improvement of perovskite solar cells. In recent years, the team has conducted in-depth research on the upper interface, buried bottom interface, and electrode buffer layer interface of perovskite solar cells, and proposed targeted defect control and performance improvement strategies. By 2023, the photovoltaic conversion efficiency of perovskite solar cells will be improved to over 25%. To further improve the photoelectric conversion efficiency, it is necessary to continue to increase the capture rate of incident photon energy by light absorbing materials on the existing basis Professor Zhu Rui from Peking University told reporters. Generally speaking, increasing the thickness of the perovskite absorber layer can enhance the absorption of incident light, thereby improving the capture ability of incident photons, obtaining more optical gain, and ultimately improving the photoelectric conversion efficiency. However, the thickening of the absorbing layer film is often accompanied by an increase in defects, leading to more severe non radiative recombination in the film, thereby reducing the photoelectric conversion efficiency of the battery and offsetting the optical gain caused by the enhanced absorption of incident light. Therefore, Zhu Rui stated that there is an urgent need to develop new processes to overcome this challenge. Facing the challenge of solving performance fluctuations from the perspective of temperature, Peking University has launched joint research with multiple research groups at home and abroad. The first challenge they encountered was the seasonal fluctuations in battery performance, where high-performance batteries typically exhibit significant seasonal dependence. This is a problem that has troubled us for over a decade Zhu Rui told reporters, "At first, we found that humidity fluctuations affected the preparation of battery functional layers, so we transferred the entire process to an inert atmosphere with controllable humidity. However, the seasonal dependence of battery performance still exists." "In addition to humidity, another factor that shows significant changes with seasonal changes is temperature." Professor Luo Deying from Beihang University suggested starting from temperature to solve the problem of performance fluctuations. So, the joint team optimized the nucleation and grain growth process of perovskite films by precisely controlling the ambient temperature during the coating stage, significantly improving the seasonal dependence of battery performance, resulting in consistent photoelectric conversion performance of batteries prepared throughout the year. In the process of searching for the mechanism, the joint team found that the high Miller index crystal faces of perovskite films are temperature dependent. Miller index is a concept in material crystallography, used to describe the sign system of crystal plane orientation, which represents the relative relationship between crystal plane and crystal axis through three integers. High Miller index refers to the crystal planes with larger index values, (100), (110), and (111) are usually considered low Miller index crystal planes, while other crystal planes are high Miller index crystal planes. The joint team found that when the ambient temperature during the coating stage of perovskite films is under specific conditions, the proportion of high Miller index (211) crystal planes in perovskite films increases. After verification, the (211) crystal plane has the characteristics of "self passivation" and the formation of "coherent grain boundaries", which significantly reduces the concentration of internal and surface defects in the film. The entire team was excited when they discovered that the (211) crystal plane had such unique properties. So, we utilized these characteristics to improve the internal and surface defects of the crystal, and further validated them in perovskite micron thick films, achieving a synergistic optimization of 'photon utilization and electrical loss' Rodying said. The joint team fully utilized the above findings to develop high-quality micrometer sized perovskite thick films, which not only improved the ability to capture incident photons, but also significantly reduced the loss of electrical energy inside the battery, successfully increasing the photoelectric conversion efficiency to 26.1% and improving the stability of the battery under external conditions such as light and heat. This study demonstrates a method for preparing thick yet high-quality perovskite thin films, which not only significantly improves the performance of solar cells, but also deepens our understanding of the working mechanism of this' fascinating material 'and provides new ideas for optimizing its performance Professor Samuel D. Stranks from the University of Cambridge in the UK stated. High Miller index crystal faces are worth exploring in depth. "Basic research plays a leading role in key core technologies, and strengthening basic research is the 'first move' to break through key core technologies." Gong Qihuang believes that conducting research on the properties of perovskite materials from the perspective of high Miller index crystal faces is a fundamental exploration in the field of perovskite optoelectronics and has important guiding significance for the development of related technologies. Other high Miller index crystal planes in perovskite materials are also worth exploring in depth. As early as the crystallographic research of semiconductor materials in the last century, high Miller index crystal planes, such as silicon and gallium arsenide crystal planes, have attracted industry attention Rodying said, "High Miller index crystal planes have more complex atomic arrangements compared to common low Miller index crystal planes, which may lead to unique surface reconstruction and unique electronic states." Li Shunde, a doctoral student at Peking University, added, "Some high Miller index crystal planes in semiconductor materials have almost no vacancies or defects. Compared with materials such as silicon and gallium arsenide, the elemental composition and crystal structure of perovskite materials are more complex and diverse, and their high Miller index crystal planes may exhibit more 'colorful' characteristics, which is worth further exploration." "This work is only the beginning of research on high Miller index crystal planes in perovskite materials. We believe that studying other high Miller index crystal faces in perovskite materials can uncover more new methods and ideas, helping to deepen our understanding of the 'high Miller index crystal face family' in perovskite materials Zhu Rui said. (New Society)