Gadolinium-doped SnO2 electron transfer layer for highly efficient planar perovskite solar cells

Metal halide perovskite solar cells have experienced unexpected rapid growth in the past decade due to their excellent photoelectric conversion efficiency. SnO2 has attracted great attention as a candidate electron transport layer to replace TiO2 in perovskite solar cells. However, the mixture of crystalline and amorphous states produces a large number of oxygen vacancy defects in the SnO2 lattice and surface, leading to nonradiative recombination at the SnO2/perovskite interface. In this work, an effective method of doping the rare earth element Gd in SnO2 is developed for planar perovskite solar cells. Doping with Gd ions can effectively passivate oxygen vacancy defects at the SnO2 interface, leading to a decrease in surface energy, which contributes to facilitating the formation of high-quality perovskite films. Gd doping can also optimize the energy level matching between SnO2 and the perovskite layer, thus improving the charge extraction and transport capabilities. As a result, the optimized device achieves a high power conversion efficiency of 22.40%, with a certified value of 21.95%.