Enhancements in device efficiency of poly(3-hexylthiophene): [6,6]-phenyl C61-butyric acid methyl ester based solar cells with incorporation of bathocuproine

► Improvement of polymer/fullerene solar cell with bathocuproine (BCP) insertion. ► BCP could effectively suppress chemical reactions between aluminum (Al) and polymer. ► No reaction occurs at active layer/BCP interface. ► Both the interfaces at blend/BCP and BCP/Al provide superior contact condition.