Sparkling hot spots in perovskite solar cells under reverse bias

•An in-situ temperature and current measurement technique with infrared micro-thermography was developed.•Infrared micro-thermography technique was used to investigate the reverse-bias behavior of perovskite solar cells (PSCs).•The sparkling hot spots were observed in PSCs under reverse bias with abruptly increased current and temperature.•The relationship between the hot spots and the photovoltaic performance of PSCs was revealed. Perovskite solar cells (PSCs) are attracting much attention and are on the way to commercialization. However, some modules are subject to reverse bias in actual fields, so it is meaningful to investigate the reverse-bias behavior of PSCs. Herein, an in-situ temperature and current measurement technique was developed. Intriguingly, some hot spots were observed and then quickly disappeared in the reverse biased PSCs, along with the simultaneous increase in the current and local temperature. Also, the potential mechanism has been revealed and analyzed. An abnormal bulge in the perovskite film was found at the hot spot. Accordingly, the appearance and disappearance of hot spots were perfectly explained by band bending and tunneling current caused by ion accumulation. Additionally, statistical analysis suggested that sparkling hot spots were related to reverse voltage and efficiencies of PSCs. The research provides a great significance for the study of PSCs under reverse bias. [Display omitted]