Enhanced performance of perovskite solar cells via defect passivation of the light-absorbing layer using 4‑tert-butylbenzylammonium iodide (tBBAI)

• The role of surface passivation agent was studied. • Lattice reconstruction and defect passivation were achieved by a simple way. • The charge recombination behavior within perovskite solar cells were investigated. • The morphological evolution of perovskite films was analyzed. Perovskite solar cells (PSCs), owing to their outstanding optoelectronic properties and low fabrication cost, have emerged as a key direction in next-generation photovoltaic technologies. However, intrinsic material defects and interfacial non-radiative recombination severely constrain their performance stability and hinder commercialization. The experimental results demonstrate that this passivation strategy, as confirmed by SEM and XRD, induces perovskite grain regrowth and reduces PbI2 content, thereby improving film crystallinity, enlarging grain size, and optimizing charge transport pathways. Consequently, the champion device achieves a power conversion efficiency (PCE) of 20.62%, representing a 13.7% enhancement over the control. XPS and FTIR analyses further confirm that tBBAI enables dual-site targeted passivation through “NH3+-Pb2+ and I–halide vacancy” interactions. Complementary characterizations including TRPL, SCLC, EIS, dark J-V, and contact angle measurements quantitatively verify extended carrier lifetimes, reduced defect density, enhanced recombination resistance, suppressed leakage current, and improved hydrophobicity, collectively leading to a substantial reduction in the hysteresis index. This work aims to further investigate the role of 4-tert-butylbenzylammonium iodide (tBBAI) as a surface passivation agent for perovskite solar cells. The molecule exhibits excellent chemical passivation capability, as demonstrated by various characterization techniques, revealing that the NH 3 + and I − functional groups interact with undercoordinated Pb 2+ ions and halide vacancies, thereby reducing surface defects and suppressing carrier recombination. Further insights into the underlying mechanism of tBBAI in the perovskite layer were systematically explored.