Enhanced charge collection with passivation of the tin oxide layer in planar perovskite solar cells

Tin oxide is an excellent candidate to replace mesoporous TiO2 electron transport layers (ETLs) in perovskite solar cells. Here, we introduced a SnO2 layer by a low-temperature solution process, and investigated its morphology, opto-physical and electrical properties affecting the device performance. We reveal that low-temperature processed SnO2 is self-passivating in nature, which leads to a high efficiency. To further enhance the blocking effect, we combined a compact TiO2 underlayer with the SnO2 contact layer, and found that the bi-layered ETL is superior compared to single layers. The best device shows photovoltaic values in a planar structure with a short-circuit current density (J(sc)) of 22.58 mA cm(-2), an open-circuit voltage (V-oc) of 1.13 V, a fill factor (FF) of 0.78, and a power conversion efficiency (PCE) of 19.80% under 1 sunlight illumination.