Exploring spin-orbital coupling effects on photovoltaic actions in Sn and Pb based perovskite solar cells

Organo-metal halide perovskites, as emerging photovoltaic materials, have demonstrated interesting spin states due to spin-orbital coupling (SOC) effects. However, replacing the Pb with the Sn can inevitably affect the SOC and consequently changes the internal photovoltaic processes in the development of environmentally friendly perovskite devices. Here, by operating the spin states with circularly polarized photoexcitation we report that the spin-dependent photocurrent (Jsc) becomes much more prominent upon replacing Pb with Sn, increasing the spin dependence from 0.25% to 1.25% by switching the photoexcitation from linear to circular polarization. Essentially, the spin-dependent Jsc is determined by the spin relaxation time, changing with the SOC strength, as compared to the charge dissociation time. On the other hand, our magneto-photocurrent (magneto-Jsc) results show that the internal magnetic parameter decreases from 281 mT to 41 mT upon Sn-Pb replacement, providing an evidence that the SOC is indeed weakened from Pb to Sn based solar cells. Furthermore, the spin-dependent photoluminescence (PL) indicates that weakening the SOC upon the Sn-Pb replacement leads to more antiparallel spin states (singlets) available for PL but less parallel spin states (triplets) available for photovoltaic action. Therefore, SOC plays an important role in the development of photovoltaic actions in Sn-based perovskite solar cells.