Non-conjugated polymers as thickness-insensitive electron transport materials in high-performance inverted organic solar cells

Two non-conjugated polymers PEIE-DBO and PEIE-DCO, prepared by quaternization of polyethyleneimine ethoxylate by 1,8-dibromooctane and 1,8-dichlorooctane respectively, are developed as electron transport layer (ETL) in high-performance inverted organic solar cells (OSCs), and the effects of halide ions on polymeric photoelectric performance are fully investigated. PEIE-DBO possesses higher electron mobility (3.68 × 10−4 cm2 V−1 s−1), higher conductivity and more efficient exciton dissociation and electron extraction, attributed to its lower work function (3.94 eV) than that of PEIE-DCO, which results in better photovoltaic performance in OSCs. The inverted OSCs with PTB7-Th: PC71BM as photoactive layer and PEIE-DBO as ETL exhibit higher PCE of 10.52%, 9.45% and 9.09% at the thickness of 9, 35 and 50 nm, respectively. To our knowledge, PEIE-DBO possesses the best thickness-insensitive performance in polymeric ETLs of inverted fullerene-based OSCs. Furthermore, PEIE-DBO was used to fabricate the inverted non-fullerene OSCs (PM6:Y6) and obtained a high PCE of 15.74%, which indicates that PEIE-DBO is effective both in fullerene-based OSCs and fullerene-free OSCs.