Surface-Activated Corrosion in Tin–Lead Halide Perovskite Solar Cells
Laura E. Mundt, Jinhui Tong, Axel F. Palmstrom, Sean P. Dunfield, Kai Zhu, Joseph J. Berry, Laura T. Schelhas, Erin L. Ratcliff
Abstract
Mixed tin–lead halide perovskite solar cells have promising power conversion efficiencies, but long-term stability is still a challenge. Herein we examine the stability of a 60:40 tin–lead perovskite to better understand diminished device performance upon thermal treatment, both in ambient and inert atmosphere. Operando X-ray diffraction shows a stable bulk structure of the perovskite absorber, leading to the hypothesis that surface chemistry dominates the degradation mechanism. X-ray photoelectron spectroscopy reveals two new observations post-thermal annealing that accompany previously reported Sn4+ evolution: (i) the formation of I3– intermediates preceding I2 loss at the surface and (ii) evidence of under-coordinated tin and lead surface sites (Snδ<2+ and Pbδ<2+, respectively) in inert and ambient conditions. These two species indicate an activated corrosion (i.e., both oxidation and reduction) process at the surface as a possible chemical pathway for degradation, which is expected to be accelerated under operando voltage and light biases.