Organic Dyes for Interfacial Regulation of Iodine in Metal Halide Perovskite Wide-Bandgap and Tandem Solar Cells

In mixed-halide wide-bandgap (WBG, FA_0.8Cs_0.2PbI_1.8Br_1.2) perovskite solar cells (PSCs), halide ion migration triggered by light exposure results in phase separation. The migrating iodide anions (I^–) undergo oxidation to iodine (I₂) upon light exposure, whereas Pb²⁺ is reduced to metallic Pb⁰. This process induces irreversible degradation of PSCs, ultimately causing a marked decline in photovoltaic performance. To mitigate this issue, a multifunctional dye molecule, 12-[3-(carboxymethyl)-5-[[4-[4-(2, 2-diphenylvinyl) phenyl]-1, 2, 3, 3a, 4, 8b-hexahydrocyclopenta [b] indol-7-yl] methylene]-4, 4′-dioxo-2′-thioxo-4, 5-dihydro −2′H, 3H-[2, 5′-bithiazolylidene]-3′(4′H)-yl] dodecanoic acid (D358), was introduced at the interface of perovskites. Under electron transfer conditions, the D358 molecule facilitated the reduction of I₂ to I^– and the oxidation of Pb⁰ to Pb²⁺, thereby effectively suppressing halide phase segregation. Furthermore, the defects of PSCs were successfully passivated by the carboxyl groups in the D358 molecule. With the adjustment, the power conversion efficiency (PCE) of the WBG device increased from 18.75 to 19.94%, indicating a significant performance improvement. When integrated with a narrow-bandgap (FA_0.6MA_0.3Cs_0.1Pb_0.5Sn_0.5I₃) subcell, a PCE of 28.83% was obtained by the all-perovskite tandem solar cells. Continuous maximum power point tracking operation for 1000 h (ISOS-L-1 standards, 25 °C) revealed superior stability in D358-treated WBG devices, preserving 82.9% of the initial PCE.