NaCl-assisted defect passivation in the bulk and surface of TiO2 enhancing efficiency and stability of planar perovskite solar cells

Abstract The defect passivation in the bulk of metal oxide electron transport layers and at the electron transport layers/perovskite interfaces is one of the pivotal roles that enhance electron injection and extraction to gain the high-performing planar perovskite solar cells. Herein, we incorporate the sodium chloride dopants into the compact TiO2 as electron transport layers at a low temperature of 200 °C. It is demonstrated that the appropriate sodium chloride additive can effectively passivate the bulk and surface defects of the intrinsic TiO2, suppressing oxygen vacancies-induced nonradiative recombination centers and improving electron extraction and collection. Simultaneously, the proper sodium chloride treatment remarkably enhances the TiO2 conductivity, reduces the water contact angle, and further indirectly optimizes the morphology of perovskite layer. With 5.0 mol% sodium chloride-incorporated TiO2, the perovskite solar cells exhibit the enhancement in the photovoltaic parameters because of the lower carrier recombination and faster charge transport, contributing to efficiency up to 19.84% with small hysteresis. More importantly, this sodium chloride-modified electron transport layer based perovskite solar cell also emerge a considerable long-term air-storage stability of about 80% of its initial efficiency after 800 h.