Investigation of the enhanced performance and lifetime of organic solar cells using solution-processed carbon dots as the electron transport layers

Easily prepared and stable solution-processed carbon dots (CDs) have been used and systematically investigated as the electron transport layers (ETLs) for both small-molecule and polymer-based solar cells. Significantly enhanced device performance and lifetime are observed. The enhanced performance is mainly driven by the improvements of the short circuit current (J(sc)) and the fill factor (FF), caused by decreasing the work function of Al electrodes and series resistance, increasing shunt resistances, and balancing electrons and hole mobility. Therefore, the devices with CDs as the ETLs have higher charge transport and collection efficiency. In addition, lifetimes of the devices with CDs as the ETLs are also significantly improved, due to the much better air-stability of CD materials compared to LiF as the ETLs. And another reason is that it can efficiently prevent the formation of an unstable cathode contact for the diffusion of Al ions at the interface. These results indicate that CDs, relatively cheap and stable materials, have great potential to be promising ETL materials for industrial-scale manufacture of organic solar cells.