Indole Carbonized Polymer Dots Doped into <i>N</i>-Oxide Functionalized Perylene-Diimide as an Electron Transport Layer for Organic Solar Cells

In organic solar cells (OSCs), the electron transport layer (ETL) is vital for high performance devices. As a widely used ETL, N-oxide-functionalized perylene-diimide (PDINO) is often limited by its low conductivity. Herein, we develop an improved ETL by doping indole carbonized polymer dots (CPDs) into PDINO. The graphitic N and oxoindole groups of CPDs could increase the self-doping of PDINO. Compared with the pristine PDINO ETL, the PDINO + CPDs ETL shows a more suitable work function and higher conductivity due to the graphitic nature of CPDs and the enhanced self-doping of PDINO. PM6:Y6 OSCs with a 10 nm PDINO + CPDs ETL demonstrate a superior average power conversion efficiency (PCE) (17.0%) compared with OSCs with only a PDINO ETL (15.6%). This improvement in PCE is attributed to the enhanced efficiency of exciton dissociation and reduced charge recombination within the devices. Furthermore, OSCs utilizing PDINO + CPDs ETL display a notable resilience to variations in ETL thickness, maintaining a high average PCE of 15.0% even when the ETL thickness is increased to 70 nm. This work provides a simple interfacial modification strategy to optimize ETLs for OSCs.