A highly efficient transition metal oxide layer for hole extraction and transport in inverted polymer bulk heterojunction solar cells

This paper demonstrates a comparative study of transition metal oxide materials, tungsten trioxide (WO3) and molybdenum trioxide (MoO3), as an effective hole extraction and transport layer in inverted polymer bulk heterojunction solar cells. Their device performances as an anode buffer layer are investigated based on thieno[3,4-b]thiophene/benzodithiophene (PTB7) and [6,6]-phenyl C70-butyric acid methyl ester(PC70BM) photoactive layers. The fabricated device with WO3 compared with MoO3 shows improved power conversion efficiency as high as 6.67% under a simulated AM1.5G illumination of 100 mW cm(-2). The excellent performance of WO3 in inverted bulk heterojunction solar cells is attributed to an efficient hole extraction, excellent electron blocking capability, smooth morphology as well as better ohmic contact between the active layer and the metal electrode.