Surface Engineering of TiO2 ETL for Highly Efficient and Hysteresis‐Less Planar Perovskite Solar Cell (21.4%) with Enhanced Open‐Circuit Voltage and Stability

Interfacial studies and band alignment engineering on the electron transport layer (ETL) play a key role for fabrication of high‐performance perovskite solar cells (PSCs). Here, an amorphous layer of SnO 2 (a‐SnO 2 ) between the TiO 2 ETL and the perovskite absorber is inserted and the charge transport properties of the device are studied. The double‐layer structure of TiO 2 compact layer (c‐TiO 2 ) and a‐SnO 2 ETL leads to modification of interface energetics, resulting in improved charge collection and decreased carrier recombination in PSCs. The optimized device based on a‐SnO 2 /c‐TiO 2 ETL shows a maximum power conversion efficiency (PCE) of 21.4% as compared to 19.33% for c‐TiO 2 based device. Moreover, the modified device demonstrates a maximum open‐circuit voltage ( V oc ) of 1.223 V with 387 mV loss in potential, which is among the highest reported value for PSCs with negligible hysteresis. The stability results show that the device on c‐TiO 2 /a‐SnO 2 retains about 91% of its initial PCE value after 500 h light illumination, which is higher than pure c‐TiO 2 (67%) based devices. Interestingly, using a‐SnO 2 /c‐TiO 2 ETL the PCE loss was only 10% of initial value under continuous UV light illumination after 30 h, which is higher than that of c‐TiO 2 based device (28% PCE loss).