Two-Terminal Perovskite/Cu(In,Ga)Se2 Tandems with Conformal Coatings Based on Commercial Bottom Cells with >26% Efficiency

Abstract

High-performance of two-terminal (2-T) perovskite/Cu(In,Ga)Se2 (PVK/CIGS) tandem solar cells (TSCs) is fundamentally limited by submicron-scale topographic irregularities inherent to commercially available CIGS substrates. We demonstrate that these features induce spatial heterogeneity in the widely adopted [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) self-assembled molecules (SAMs), resulting in non-conformal PVK deposition due to poor wettability. By developing a N,N-dimethylformamide (DMF) assisted hydrophilic-terminated SAM reconstructing Me-4PACz interface strategy, we achieved conformal coverage of SAM and PVK. Furthermore, we identify that conformal PVK layer inherit substrate textures with defects-rich, impeding homogeneous C60 evaporation and conformal capping. To address this, we devised a bimolecular synergistic surface self-accumulation (BSSS) strategy combining 2,3,4,5,6-pentafluorobenzylphosphonic acid (F5BPA) and p-trifluoromethylphenyl ethylamine (p-CF3PEA). These modifiers spontaneously concentrate on textured PVK surfaces to construct a uniform interfacial network that recasts the PVK surface and bridges C60 through enhanced interactions. This enables homogeneous C60 adsorption and minimizes interfacial contact losses. The resulting 2T PVK/CIGS TSCs achieve a power conversion efficiency (PCE) of 26.14% (independently certified 25.21%), significantly surpassing previous records.