Charge Carrier and Mobile ion Dynamic Processes in Perovskite Solar Cells: Progress and Prospect

Abstract

Perovskite solar cells have achieved emerging conversion efficiency exceeding 25% in less than one decade, comparable to the record efficiency of silicon solar cells. Therefore perovskites attract considerable research interest as excellent materials of light-harvesting due to their great potential for the next generation of high-efficiency low-cost photovoltaics, in particular flexible solar cells that fill the gap of silicon photovoltaics. The excellent performance of photovoltaics is generally ascribed to the unique optoelectronic properties, which also make perovskites excellent candidates for other photonics applications. Charge carrier dynamics are significantly relevant to the conversion efficiency of a solar cell, and therefore the charge carrier dynamics have been intensively investigated in recent years by various time-resolved spectroscopic techniques. Different from the conventional semiconductors, perovskites are mixed ionic–electronic conductors, and mobile ions play important roles in the performance of the photovoltaics. The interaction between mobile ions and charge carriers exhibit a significant impact on the carrier dynamics and eventually on the conversion efficiency and stability of performance. This chapter reviews the progress of the investigation of charge carriers in perovskite photovoltaics. In the femtosecond timescale, a significantly slowed cooling of hot carriers is confirmed, which is promising to hot carrier solar cells and probably high-efficiency photocatalysis in the future. Charge carrier recombination has been intensively investigated. Defect trapping, charge carrier transport and transfer, and carrier recombination in the interface are closely relevant to the conversion efficiency and stability. Mobile ions are confirmed to play an important role in the carrier dynamics in the macroscopic timescale. I-V hysteresis and stability of the performance are usually considered to correlate to the mobile ions. In the final section, we discuss the problems that require urgent attention in perovskite solar cells for performance improvement and commercialization.