Erbium-doped CsPbI2.5Br0.5 with enhanced crystalline quality and improved carrier lifetime for thermally stable all-inorganic perovskite solar cells

Abstract

In recent years, all-inorganic perovskite solar cells (AIPSCs) have attracted enormous attention because of their excellent stability compared to organic–inorganic hybrid PSCs. However, the pinholes and cracks on the film surface caused by the fabrication process usually result in restricted light absorbance and short carrier lifetime; therefore the photoelectric conversion efficiency (PCE) of AIPSCs is difficult to reach a high value. To solve this issue, here we propose the lattice doping of rare earth element erbium (ErCl₃) into CsPbI_2.5Br_0.5 perovskite films. We present that chloride ions (Cl⁻) can assist in the formation of the perovskite phase and enhance the crystallinity and uniformity of perovskite thin films, thus significantly prolonging the carrier lifetime and improving the photovoltaic performance of the AIPSCs. Moreover, the radius of erbium ions (Er³⁺) is smaller than that of lead ions (Pb²⁺), so Er-doping will lead to a contracted lattice volume and enhanced phase thermal stability. The fabricated AIPSCs with nanocarbon as both the hole transport layer and counter electrode can reach a champion PCE of 9.22%. Furthermore, the encapsulated AIPSCs exhibit a superior heat resistance in an ambient atmosphere and retain 95% of their initial PCE after being continuously heated at 100 °C for over 576 h. This study helps tackle the issue of excessive crystal defects in the preparation process of inorganic perovskites and provides a feasible solution for fabricating AIPSCs with excellent thermal stability.