Abstract
Surface passivation of perovskite solar cells (PSCs) has been considered as an effective way to improve the efficiency and stability of devices. Here, we study the influence of an ultrathin layer of tantalum pentoxide (Ta2O5) as a passivation layer in the mesoscopic heterojunction PSCs. This material was conformally coated on top of mesoporous TiO2 (mp-TiO2) with various thicknesses by the atomic layer deposition technique. We observe that Ta2O5 reduces the recombination at the perovskite/mp-TiO2 contact surface and improves the charge transport, as proved by photoluminescence spectroscopies. With an optimized thickness of Ta2O5 (similar to 1.9 nm), a high-power conversion efficiency of 21.25% was obtained for the Ta2O5-modified device, mostly because of the enhancement of the open-circuit voltage (V-oc). In addition, our modified cell exhibits low hysteresis, improved shelf life, and thermal and UV light stabilities compared to the unmodified device. Our study demonstrates the importance of surface passivation in mesoscopic PSCs.