Effect of buffer layers on the performance of organic photovoltaic cells based on copper phthalocyanine and C₆₀

The interface formed between fullerene (C₆₀) and cathode is a potential limiting factor to the performance of organic photovoltaic (OPV) cells based on copper phthalocyanine (CuPc)/C₆₀ heterojunctions. The influence of buffer layer on the performance of OPV cells was studied by usingbathophenanthroline (Bphen), 1,3,5-tris(2-N-phenylbenzimidazolyl) benzene (TPBi) and tris-8-hydroxy-quinolinato aluminum (Alq₃) to substitute for the bathocuproine (BCP) buffer layer between C₆₀ and Ag. It was found that the devices with different buffer layers exhibited both improved photovoltaic response and lower series resistance. Also, the defect states in the buffer layer indicate that buffer layers with appropriate film thickness can protect C₆₀ film from deterioration during Ag deposition and effectively improve charge carrier transportability. In addition, device stability has also been enhanced, particularly devices with Bphen and TPBi as buffer layers have achieved a shelf-lifetime of 1700 min in air at ambient circumstance.