Uniform and ordered self-assembled hole-selective layers driven by π-π interactions for efficient perovskite-silicon tandem solar cells

Self-assembled molecules (SAMs) are promising hole-selective layers for high-performance perovskite tandem solar cells. However, their inhomogeneous distribution and disordered packing on substrates lead to interfacial energy losses, limiting further improvements in efficiency and stability. Here, we design a SAM, Me-Ph2mPACz, through meta-disubstitution of dimethylcarbazole moieties on a phenyl linker. Compared to its monosubstituted carbazole counterpart, Me-PhpPACz, Me-Ph2mPACz exhibits stronger adsorption energy and suppresses intermolecular hydrogen bond interaction via π-π stacking interactions. This inhibits the formation of large micelles, promoting a uniform, ordered and thermoresistant hole-selective layer. The resulting multilayer configuration retards crystallization and alleviates residual stress in the perovskite film, thereby reducing non-radiative recombination at the buried interface and enhancing hole extraction. The implementation of Me-Ph2mPACz as the hole-selective layer in 1.68 eV perovskite solar cells reduces interfacial non-radiative losses from 168 mV to 124 mV, accompanied by an increase in power conversion efficiency from 21.82% to 23.14%. The corresponding perovskite-silicon tandem solar cells achieve a champion PCE of 33.40% (certified 32.45% at National Renewable Energy Laboratory, NREL). Furthermore, encapsulated tandem devices based on Me-Ph2mPACz demonstrate exceptional stability, retaining 83% of their initial efficiency after 1000 h of maximum power point tracking under one-sun illumination at 85 °C in air. This work opens an avenue for designing high-performance and durable self-assembled molecules for perovskite tandem photovoltaics.