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 (Pb2+ ). 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 (KAcCl2 ) 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 (AcCl2 ) can form Pb-Cl and Pb-O bonding as "dual anchoring" bonds with residual Pb2+ , resulting in strong binding force and effective passivation of residual Pb2+ defects. Furthermore, K+ can enlarge grain size and restrain ion migration at the grain boundaries. Consequently, perovskite solar cells with KAcCl2 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.
Keywords: bidentate coordination; perovskite solar cells; potassium dichloroacetate; sequential deposition method; unreacted lead iodide.
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