Tailored Key Parameters of Perovskite for High-Performance Photovoltaics

Abstract

ConspectusTo tackle the foreseen energy crisis and serious environmental problem caused by conventional energy resources, solar cells, or photovoltaics (PV), a technology that can directly convert sunlight to electricity has been considered to be one of the most important and cost-effective clean energy techniques that benefit the environment. So far, silicon-based PVs have dominated the market due to mature fabrication techniques and their relatively good power conversion efficiency (PCE) and excellent stability.In the past decades, metal halide perovskite PVs have been a major direction of current PV research owing to their intriguing optoelectronic performance. The record PCE of perovskite PV cells has unprecedently increased from an original 3.8 to 25.5%. The typical structure of a photovoltaic perovskite is ABX3, where A refers to a monovalent cation such as methylammonium (MA+), cesium (Cs+), or formamidinium (FA+); B refers to a divalent cation such as Pb2+ or Sn2+; and X refers to a halide anion. In general, a perovskite PV device consists of an active layer of the perovskite absorber, which is connected by a hole-transporting layer (HTL) and an electron-transporting layer (ETL). In the beginning, the strategies to improve the PCEs mainly focused on developing an effective method to grow a smooth and continuous polycrystalline film. After the improvement of the baseline PCE of the perovskite PVs, various techniques were employed to reduce the defects of perovskite formed at grain boundaries and surfaces, further pushing the PCEs of perovskite PV devices to over 20%. In the meantime, the discovery of suitable and low-cost interfacial materials such as electron-transporting materials and hole-transporting materials has appealed to the attention of the perovskite research community to accelerate the commercialization of the perovskite PVs.In this Account, we start from our efforts to develop facile and effective fabrication strategies to obtain smooth and continuous polycrystalline perovskite thin films, including vapor-assisted and moisture-assisted perovskite crystal growth. The strategies and the in-depth mechanisms of preventing the formation of specific detrimental defects accumulated at grain boundaries or the surface are also portrayed by designing various passivation molecules with certain functional groups, such as carbonyl groups, amine groups, or sulfonic groups. Some systematically designed electron- or hole-transporting materials to improve the charge extraction and collection efficiency in perovskite PV devices are discussed as well. Finally, future perspectives for further enhancing the long-term stability and PCE are proposed to accelerate the commercialization of perovskite PV devices in the next decade.