Homogenizing hole-selective contacts for centimeter-square flexible perovskite/Cu(In,Ga)Se ₂ tandems

Abstract

(CIGS) tandems offer a path to high-efficiency and lightweight photovoltaics. However, simultaneously achieving high efficiency and mechanical durability remains a challenge. A contributing factor is the interfacial inhomogeneity arising from molecular aggregation in planar carbazole-based hole-selective contacts (HSCs) on flexible substrates. Here, we develop a strategy of spatial steric hindrance that transforms planar carbazole core into a three-dimensional π-conjugated skeleton. This molecular reconfiguration suppresses intermolecular π-π stacking, yielding homogenized selective contacts and high-quality perovskite films. When integrated into flexible monolithic perovskite/CIGS tandem devices, this strategy enabled a champion stabilized power conversion efficiency (PCE) of 26.2% (certified 25.5%) for a 0.091-square centimeter device and 25.3% (certified 24.3%) for a centimeter-scale device, both representing high certified efficiencies reported to date for flexible two-terminal tandems. These devices demonstrated remarkable mechanical robustness, retaining their initial PCE after 10,000 bending cycles at a 10-millimeter radius, highlighting the potential of molecular-level interfacial engineering to realize high-efficiency, stable, and scalable flexible photovoltaics.