This thesis explores two interfacial strategies to improve the performance of lead-free tin-based perovskite solar cells (TinPSCs). First, bio-inspired antioxidant molecules—adrenaline, 3,4-dihydroxyhydrocinnamic acid (DHCA) and 3,4-dihydroxy-L-phenylalanine (L-DOPA)—were applied as surface or bulk additives to mitigate Sn²⁺ oxidation and passivate undercoordinated Sn ions. Although these treatments showed partial improvements in stability, their strong reducing nature sometimes led to Sn⁰ formation and crystallization issues, limiting device efficiency. Building on these findings, an alternative interfacial modification approach was developed using 4-fluorophenethylammonium iodide (4FPEAI) deposited onto the PEDOT:PSS layer. The fluorine atom reacts sulfonate atom through hydrogen bonding and induced dipole formed a built-in electric field that enhanced hole extraction and suppressed interfacial charge carrier recombination. Devices treated with 4FPEAI showed improved crystallinity, reduced trap state density, and increased hole mobility. Additionally, incorporation of 2 mol% ammonium thiocyanate (NH₄SCN) into the perovskite precursor further improved the open-circuit voltage (VOC) by modulating crystallization kinetics and enhanced photovoltaic performance with a champion power conversion efficiency (PCE) of 10.47%. Characterization via space-charge-limited current (SCLC), photoluminescence (PL), time-resolved photoluminescence (TRPL), Raman, and impedance spectroscopy confirmed the combined effects of trap passivation and improved charge transport. Grazing-incidence wide-angle X-ray scattering (GIWAXS) reveals the crystallization mechanism. This work highlights the complementary roles of redox chemistry and interfacial dipole engineering in advancing efficient and stable TinPSCs.