Sn–N/Sn–O interaction improving electron collection in non-fullerene organic solar cells†
The electron transporting layer (ETL) is critical for achieving high performance and high stability of non-fullerene organic solar cells. However, the commonly used ZnO ETLs have the disadvantage of poor device photo-stability. Although aqueous SnO2 can yield better stability of devices, an “S” shape is observed in the current density–voltage (J–V) characteristics resulting in poor device performance when it is used as an ETL in non-fullerene organic solar cells. In this paper, we have developed a method of modifying an aqueous SnO2 solution by adding polyethylene oxide (PEO) or polyethylenimine (PEI) to eliminate the “S” shape characteristic of organic solar cells. PEO and PEI can interact with SnO2 to form favorable interface dipoles and reduce the work function of the ETL films, which improves charge collection. In addition, the work function of the PEO or PEI modified SnO2 shows better photo-stability than that of ZnO, and the devices based on the modified SnO2 ETL also achieve higher photo-stability compared to the ZnO reference device.