Scalable Solution‐Processed Hybrid Electron Transport Layers for Efficient All‐Perovskite Tandem Solar Modules

Abstract All‐perovskite tandem solar cells offer the potential to surpass the Shockley–Queisser (SQ) limit efficiency of single‐junction solar cells while maintaining the advantages of low‐cost and high‐productivity solution processing. However, scalable solution processing of electron transport layer (ETL) in p‐i‐n structured perovskite solar subcells remains challenging due to the rough perovskite film surface and energy level mismatch between ETL and perovskites. Here, scalable solution processing of hybrid fullerenes (HF) with blade‐coating on both wide‐bandgap (≈1.80 eV) and narrow‐bandgap (≈1.25 eV) perovskite films in all‐perovskite tandem solar modules is developed. The HF, comprising a mixture of fullerene (C₆₀), phenyl C₆₁ butyric acid methyl ester, and indene‐C₆₀ bisadduct, exhibits improved conductivity, superior energy level alignment with both wide‐ and narrow‐bandgap perovskites, and reduced interfacial nonradiative recombination when compared to the conventional thermal‐evaporated C₆₀. With scalable solution‐processed HF as the ETLs, the all‐perovskite tandem solar modules achieve a champion power conversion efficiency of 23.3% (aperture area = 20.25 cm²). This study paves the way to all‐solution processing of low‐cost and high‐efficiency all‐perovskite tandem solar modules in the future.