Interfacial engineering via inserting functionalized water-soluble fullerene derivative interlayers for enhancing the performance of perovskite solar cells

For n–i–p type perovskite solar cells (Pero-SCs), one of the limitations which hinder the improvement of device performance is the extremely low electrical conductivity of the TiO₂ electron transport layer (ETL). Herein, two novel functionalized water-soluble fullerene derivatives C₆₀O_∼18(OH)_∼10(NH₂)_∼8 (f-C₆₀) and C₇₀O_∼18(OH)_∼10(NH₂)_∼10 (f-C₇₀) were prepared and utilized as buffer layers between ITO and a vacuum-deposited fullerene C₆₀ ETL in Pero-SCs. After inserting f-C₆₀ and f-C₇₀ layers, the Pero-SCs showed an enhanced crystallinity of the perovskite film, more efficient charge transport, reduced recombination and a decreased charge-transport resistance. Therefore, a summit power conversion efficiency (PCE) of 16.97% was achieved for the device with the f-C₆₀/C₆₀ ETL, which was ∼24% higher than that of the control device (13.71%). The PCE of the Pero-SC based on the f-C₇₀/C₆₀ ETL also exhibited a 16% enhancement. This work demonstrated the great potential of f-C₆₀ and f-C₇₀ for application as ETLs in Pero-SCs.