Suppressing Residual Lead Iodide and Defects in Sequential-Deposited Perovskite Solar Cell via Bidentate Potassium Dichloroacetate Ligand.

In sequential-deposited polycrystalline perovskite solar cells, the unreacted lead iodide due to incomplete conversion of lead iodide to perovskite phase, can contribute to ionic defects, such as residual lead ions (Pb ). At present, passivation of interfacial and grain boundary defects has become an effective strategy to suppress charge recombination. Here, we introduced potassium acetate (KAc) and potassium dichloroacetate (KAcCl ) as additives in the sequential deposition of polycrystalline perovskite thin films and found that acetate ions (Ac ) can effectively reduce the residual lead iodide. Compared with acetate (Ac), dichloroacetate (AcCl ) can form Pb-Cl and Pb-O bonding as "dual anchoring" bonds with residual Pb , resulting in strong binding force and effective passivation of residual Pb defects. Furthermore, K can enlarge grain size and restrain ion migration at the grain boundaries. Consequently, perovskite solar cells with KAcCl additive show power conversion efficiencies (PCE) from 19.67 % to 22.12 %, with the open-circuit voltage increasing from 1.06 V to 1.14 V. The unencapsulated device can maintain 82 % of the initial PCE under a humidity of 30±5 % for 1200 h. This work provides a new approach for the regulation of ionic defects and grain boundaries at the same time to develop high-performance planar perovskite solar cells.