Investigation into effects of electron transporting materials on organic solar cells with copper phthalocyanine/C60 heterojunctions

In this work, we used copper phthalocyanine (CuPc), tris(8-hydroxyquinolato) aluminum and 2-(4-biphenyl)-5-(4-tert-butylphenyl)1,3,4-oxidiazole to replace bathocuproine (BCP) as an electron transporting layer (ETL) in photovoltaic devices based on CuPc/C60 heterojunctions. Devices using the four materials as ETLs exhibit efficient photon-to-electron conversion under illumination. The finding suggests that electrons collection from C60 to Al cathode should be unrelated to the lowest unoccupied molecular orbital levels and band gaps of ETL materials. In addition to competitive light-to-electricity conversion efficiency, device stability has been improved using CuPc as an ETL compared to the BCP-based device. Mechanisms behind the phenomena were discussed.