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. SnO 2 has attracted great attention as a candidate electron transport layer to replace TiO 2 in perovskite solar cells. However, the mixture of crystalline and amorphous states produces a large number of oxygen vacancy defects in the SnO 2 lattice and surface, leading to nonradiative recombination at the SnO 2 /perovskite interface. In this work, an effective method of doping the rare earth element Gd in SnO 2 is developed for planar perovskite solar cells. Doping with Gd ions can effectively passivate oxygen vacancy defects at the SnO 2 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 SnO 2 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%. • Gd was first introduced into SnO 2 -based planar PSCs. • Gd doped SnO 2 PSCs achieved the best efficiency of 22.4%. • Gd doping reduces interfacial trap-assisted charge recombination. • Gd doped SnO 2 exhibited a better energy level arrangement with the perovskite.