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-reconstructed Me-4PACz interface strategy, we achieved conformal coverage of SAMs and PVK. Furthermore, we identify that the conformal PVK layer inherits substrate textures with rich defects, 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 2-T PVK/CIGS TSCs exhibit a power conversion efficiency (PCE) of 26.14% (independently certified 25.21%), significantly surpassing previous records.