Composition design of fullerene-based hybrid electron transport layer for efficient and stable wide-bandgap perovskite solar cells

Fullerene derivatives [6,6]-phenyl-C61-butyric acid methyl ester (PC₆₁BM) has been routinely used as the electron transport layer (ETL) in perovskite solar cells due to its suitable energy levels and good solution processability. However, its electron mobility and conductivity still need to be further enhanced for constructing high performance perovskite solar cells (PSCs). Herein, by doping the PC₆₁BM with a p-type polymer PM6 and n-type molecule ITIC, efficient wide-bandgap perovskite solar cells with improved efficiency and operational/storage stability are obtained. Further spectroscopy and electric measurements indicate PM6 and ITIC can both passivate defects at the perovskite/ETL interface, meanwhile ITIC can elevate the Fermi level of PC₆₁BM to enhance conductivity and PM6 can improve the photo-induced electron mobility of the ETL, facilitating charge extraction and reducing charge recombination. As the results, Cs_0.17FA_0.83Pb(I_0.83Br_0.17)₃ wide-bandgap PSCs with PM6:PC₆₁BM:ITIC as the ETL demonstrates a superior efficiency of 22.95%, compared to 20.89% of the PC₆₁BM assisted device.