Developments of Highly Efficient Perovskite Solar Cells

ConspectusAfter developments in just more than a decade, the power conversion efficiency (PCE) of single junction perovskite solar cells (PSCs) has achieved a record of 26.0%. Such rapid progress of PSCs technology is mainly attributed to the excellent optoelectronic properties and facile solution-processed fabrication. Starting from the birth of PSCs up to present, various methods have been attempted to improve the performance and/or stability of PSCs. The first perovskite photovoltaic devices achieved a very low efficiency, attributed to the poor quality of the perovskite film upon a mesoporous substrate. There then are large amounts of work aiming at high-quality light-absorber films with pin-free, dense, homogeneous morphology with high crystallinity. Hereafter, the developments of carrier transport materials/layers (CTLs) based on different device structures had become an important issue. The stable CTLs with excellent electrical properties and matched energy levels are desired for efficient and stable PSCs. Besides perovskite film growth control and employment of advanced CTLs, the main studies are mitigation of all kinds of defects in PSCs, including charge traps in the perovskite bulk, interface defects between the perovskite and adjacent CTLs, and grain boundaries located at dangling bonds as well as halide loss defects. All of these defects in PSCs can not only cause nonradiation recombination but also provide an extra pathway for ionic migration, which leads to irreversible degradation of the perovskite film. And the very current studies on defects are trying to push PSCs to industrial application, since the long-term stability and high-efficiency count as the same importance for PSCs. There is an apparent fact that the literature about PSC fabrication is based on different experiment conditions, which gives it poor reproducibility. Herein, the conception and motivation of the studies are more valuable. It is necessary to share the research in detail by individual laboratories for a better communication in this rapidly developed field. It could be concluded that there are mainly three steps for PSCs to achieve such high-efficiency and appreciable stability: 1) modulation of the perovskite film quality; 2) development of desired CTLs for PSCs; 3) mitigation of defects in the perovskite bulk and/or interfaces. The three steps are also the basic development track of PSCs. In this Account, we will briefly review the milestones in the early period of PSCs. Then, we will mainly focus on our group and coauthors' representative progress of high-efficiency PSCs, following the above development order of PSCs technology. The mechanisms and motivations of improved efficiency and stability in different stages are discussed. Finally, a comprehensive summary as well as the deep perspectives of PSCs are proposed. And the future directions of PSCs for practical application are also discussed.