A non-equilibrium Ti4+ doping strategy for an efficient hematite electron transport layer in perovskite solar cells

Abstract

Non-equilibrium Ti⁴⁺-doped hematite (Ti-Fe₂O₃) is explored successfully as an electron transporting layer (ETL) material for planar perovskite solar cells, which were simply processed by quenching the ETL films at high temperature after thermal annealing. High-temperature quenching can fix Ti⁴⁺ dopants in the bulk lattices of Ti-Fe₂O₃ and suppress surficial TiO_x segregations on it, which obviously increase the doping density and decrease surficial electron traps in Ti-Fe₂O₃ ETLs, thereby greatly improving their electron transport properties. Hence, the efficiency of planar perovskite solar cells with these desired Ti-Fe₂O₃ ETLs can be boosted to 17.85% along with the stabilized value of 17.05%, which is much higher than that of cells with Ti-Fe₂O₃ ETLs prepared by routine natural cooling and even the previous record efficiency of planar cells based on Fe₂O₃ ETLs. Our work contributes to enriching the ETL systems of perovskite solar cells and offers a promising candidate for efficient and photo-stable cells.