Controlled Activation of Self‐assembled Molecules Enabling Reproducible Flexible Perovskite/Cu(In,Ga)Se ₂ Tandems

Monolithic perovskite/Cu(In,Ga)Se 2 (CIGS) tandem solar cells offer a promising route toward lightweight and flexible photovoltaics beyond the Shockley–Queisser limit, for which self‐assembled molecule (SAM)‐based hole‐selective layer (HSL) is particularly attractive. However, in perovskite/CIGS tandems, the interfacial robustness of SAM‐based HSLs is often compromised by insufficient molecular anchoring, especially on rough and flexible substrates, leading to nonuniform assembly, enhanced non‐radiative recombination, and poor device reproducibility. Here, we introduce a controlled molecular activation strategy for SAM‐based HSLs by incorporating a trace amount of potassium hydroxide into the SAM precursor. This treatment induces controlled deprotonation of phosphonic acid groups, generating reactive phosphonate species that facilitate rapid covalent bonding with the substrate during self‐assembly, thereby yielding a dense and robust molecular interface. As a result, wide‐bandgap perovskite solar cells achieve a power conversion efficiency of 22.7% (0.0665 cm 2 ) with markedly narrowed device‐to‐device distributions in PCE, V OC , FF, and J SC , indicative of improved reproducibility. Applied to flexible monolithic perovskite/CIGS tandem solar cells, the resulting devices achieve a PCE of 25.3% (0.075 cm 2 ) and retain 92.6% of their initial efficiency after 500 h of maximum power point tracking at 45°C.