Conjugation-regulated self-assembled molecules for tandem solar cells

Perovskite/silicon tandem solar cells on rough textured substrates are at present limited by a critical trade-off in self-assembled monolayer (SAM) design because increasing molecular conjugation enhances conductivity but often leads to unfavourable aggregation that impairs conformal coverage^1,2. Here we overcome this challenge using a rationally engineered molecular spatial conjugation that incorporates tailored intramolecular distortion to suppress excess π-π stacking without sacrificing charge-transport efficiency. This steric regulation facilitates the formation of a highly ordered, conformal SAM across rough pyramidal textures. By reconciling molecular packing with interfacial coverage, the tailored interface provides optimized energy-level alignment for ultrafast charge extraction, enables improved defect passivation through adaptive conformational adjustment and acts as a robust template for high-quality perovskite film growth. Making use of this interface, the optimized tandem device achieves a notable fill factor (FF) of 85%, yielding a certified stabilized power conversion efficiency (PCE) of 35.1%. Furthermore, the device demonstrates outstanding stability, retaining more than 94% of its initial performance after 1,500 h of ageing under the ISOS-L-1 protocol. Our findings provide a clear molecular engineering route to reconcile conductivity and film uniformity while maximizing the performance of tandem photovoltaics on textured silicon substrates.