Open-circuit-voltage improvement mechanism of perovskite solar cells revealed by operando spin observation

Abstract Organic-inorganic hybrid perovskite solar cells have attracted much attention as one of the most important next-generation solar cells. The solar-cell performances are known to be changed under operation; however, the root cause of the instability has not yet been understood sufficiently. Here, we report improvement mechanism in the open-circuit voltage, V OC , of perovskite solar cells at the initial stage of device operation that were firstly investigated by electron spin resonance (ESR). ESR study reveals reverse electrons transfer at the interface from the perovskite layer to the hole-transport layer not only under dark conditions but also under light irradiation where electrons are subsequently trapped in the hole-transport layer. Thereby, an electron barrier is enhanced at the perovskite/hole-transport-layer interface, improving field-effect passivation at the interface, and thus the V OC improves. These findings are crucial for understanding the mechanisms of device performance changes under operation, showing a relation between reverse electrons transfer and performance improvement, which is valuable for the development of further efficient perovskite solar cells.