Metal-Organic Complex Interfaces Enabling Triplet-State Modulation and Defect Passivation in Perovskite Solar Cells

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Abstract
Incorporating metal-organic complexes into perovskite solar cells (PSCs) can be a suitable strategy to improve device performance via surface defects passivation with further modulation into interfacial charge-carrier dynamics. Moreover, can also enable photophysical processes like metal-to-ligand charge transfer (MLCT) and triplet-triplet annihilation (TTA), sensitizing PSCs active layer and enhancing light harvesting capability. Here, Pt(II)- and Zn(II)-based Salophen and Sal-3,4-ben complexes were employed as interfacial modifiers, with Pt(Sal-3,4-ben) yielding the most significant improvement in photovoltaic performance. Perovskite films incorporating Pt(Sal-3,4-ben) have longer charge-carrier lifetimes, as typical of strong spin-orbit coupling from the heavy Pt center and by TTA-induced charge injection into the perovskite bands. An increase in open-circuit voltage (VOC) (1.07 to 1.12 V) and in short-circuit current density (JSC) (22.18 to 24.31 mA cm-2) is observed together an improvement in fill factor and series resistance reduction. This suggests trap-state passivation and more efficient charge separation/extraction, probably arising from triplet-state processes. Involving excited triplet states may facilitate TTA or delayed fluorescence, indirectly boosting photocurrent generation originated from charge transfer process involving Pt(II) coordination compound and perovskite. In contrast, Zn-based complexes, which lack heavy atoms, exhibit limited triplet-state process resulting in modest improvements, supporting the proposed link between triplet-mediated effects and enhanced JSC. Overall, these results highlight the dual role of metal complexes in both defect passivation and photophysical tuning of PSCs, offering a new platform for exploring triplet-state and singlet-fission engineering toward higher efficiency.