Ethylenediamine Vapors-Assisted Surface Passivation of Perovskite Films for Efficient Inverted Solar Cells

Defects present at the surface or within the bulk of halide perovskites act as a barrier to charge transfer/transport, induce nonradiative recombination thereby limit open-circuit voltage (V-OC), and accelerate degradation in the perovskite solar cells (PSCs). Passivation of these defects at surfaces, interfaces, and grain boundaries to suppress the charge recombination is therefore imperative to improving photovoltaic performance in the PSCs. Herein, a facile posttreatment of perovskite surface by ethylenediamine (EDA) via mixed solvent vapor annealing method is reported. The results show that only a trace amount of EDA causes significant suppression of nonradiative recombination leading to over 100 mV increased V-OC and approximate to 22% improvement in power conversion efficiency (PCE) of the inverted PSCs. The key reasons for this improvement are an upward shift in the Fermi energy level, reduced lattice strain and Urbach energy, and reduction in nonradiative recombination upon EDA passivation. These lead to a PCE exceeding 20% up from 16% for a nonpassivated film. The unencapsulated EDA-modified PSCs also demonstrate an improved shelf-life and retain 87% of the initial PCE after 850 h.