Synergistic effect of anions and cations in additives for highly efficient and stable perovskite solar cells

Abstract

Organic–inorganic halide perovskites have attracted intensive attention due to their outstanding photophysical properties and high performance in optoelectronic devices. Moreover, the quality of perovskite films plays an important role in the performance of perovskite devices. The use of additives has been previously suggested as the simplest and effective method to improve the quality of perovskite films. However, only the cations or anions in most additives are capable of functioning as active species in improving the quality of perovskite films. Herein, we report that ammonium thiocyanate (NH₄SCN) as an additive (contains NH₄⁺ and SCN⁻ ions) can significantly improve the quality of perovskite films as compared to NH₄I and Pb(SCN)₂ as additives containing the single active species of NH₄⁺ and SCN⁻, respectively. The synergistic effect between the ions in NH₄SCN is favorable for controlling the nucleation and growth speed of the crystal grains, which evidently increases the grain size and markedly improves the film stability. Finally, the efficiency of the device based on NH₄SCN (16.47%) is significantly enhanced without a hysteresis effect as compared to that of the devices with single ions as the active species, e.g., NH₄⁺ in NH₄I (13.97%) and SCN⁻ in Pb(SCN)₂ (12.88%). Our findings suggest that the synergistic effect of anions and cations in additives is an effective strategy for realizing efficient and stable perovskites.