Performance Enhancement of Flexible Perovskite Solar Cells Enabled by Ammonium Halide Passivation

The low-temperature preparation requirement of perovskite solar cells (PSCs) enables the fabrication of flexible perovskite solar cells (f-PSCs). This technique has great potential for commercialization but is still accompanied by challenges in preparing dense and low-defect perovskite films on flexible polymer substrates. In this work, propylammonium chloride (PACl) was introduced during the fabrication process of a two-step sequentially deposited perovskite film. This ammonium halide salt has a long alkyl chain that can be incorporated into the A sites lacking volatile cations in the perovskite lattice. Meanwhile, it can also induce the transformation of extended imperfections to a lower-dimensional perovskite material. By using PACl for interface treatment, 2D perovskite is formed on 3D perovskite, which passivates interface defects in perovskite thin films, inhibits ion migration at grain boundaries, and restrains hysteresis. By comparison, the n-i-p f-PSCs passivated by PACl have an exceptional power conversion efficiency (PCE) of 22.06%, an open-circuit voltage (V-OC) of 1.19 V, and a fill factor (FF) of 79.02% without any deterioration in the short-circuit current density (J(SC)), which are superior to control device parameters (PCE & horbar;19.24%, V-OC & horbar;1.11 V, and FF & horbar;76.09%). In addition, the PACl-passivated flexible device exhibited decent mechanical stability, where the stimulated PCE was maintained at 89% of the original value after 2000 cycles of bending tests with a bending radius of 5 mm.