Effects of Spin States on Photovoltaic Actions in Organo-Metal Halide Perovskite Solar Cells Based on Circularly Polarized Photoexcitation

Abstract

Organo-metal halide perovskites have become very promising photovoltaic materials with triply nondegenerate spin states due to spin–orbital coupling effects. This paper reports the effects of optically operated spin states on photocurrent (JSC) and photovoltage (VOC) in perovskite (MAPbI3) solar cells with the device architecture of ITO/TiO2 (compact)/TiO2 (mesoporous)/MAPbI3/P3HT/Au. Specifically, we switch the photoexcitation from linear polarization to circular polarization to change the electron–hole pair population of spin singlet φml=±1φ↑e↓h and spin triplet φml=0φ↑e↑h in the perovskite solar cells. Simultaneously, we investigate the photovoltaic actions upon optically shifting the spin population. We find that optically shifting the spin population by switching photoexcitation from linear to circular polarization can cause an increase on both JSC and VOC in the perovskite solar cells under circular photoexcitation. Our studies present the first evidence that the perovskite solar cells are the only type of solar cells where spin states can be optically operated with the consequence of influencing the photovoltaic actions. Our results indicate that switching photoexcitation from linear to circular polarization can increase the population of spin triplet electron–hole pairs available for dissociation and consequently increases the JSC. On the other hand, optically shifting the spin population can decrease the bulk polarization and consequently increases the VOC under circular photoexcitation. Therefore, our studies provide insightful understanding on the effects of optically operating spin states on photovoltaic processes in perovskite solar cells.