Efficient small-molecule organic solar cells incorporating a doped buffer layer

Abstract Small-molecule organic solar cells (OSCs) with an optimized structure of indium tin oxide/poly (3,4-ethylenedioxythioxythiophene):poly(styrenesulfonate)/copper phthalocyanine (CuPc) (10 nm)/CuPc: fullerene (C 60 ) mixed (20 nm)/C 60 (20 nm)/4,7-diphenyl-1,10-phenanthroline (BPhen) (5 nm)/Ag were fabricated. In this study, the cesium carbonate-doped BPhen (Cs 2 CO 3 :BPhen) was adopted as the buffer layer to enhance the efficiency of the OSCs. The photovoltaic parameters of the OSCs, such as the short-circuit current density and fill factor, depend on the doping concentration of Cs 2 CO 3 in the BPhen layer. The cell with a Cs 2 CO 3 :BPhen (1:4) cathode buffer layer exhibits a power conversion efficiency (PCE) of 3.51%, compared to 3.37% for the device with the pristine BPhen layer. The enhancement of PCE was attributed to the energy-level alignment between the C 60 layer and the Cs 2 CO 3 :BPhen layer. In addition, the characterization measured using atomic force microscopy shows that the Cs 2 CO 3 :BPhen layers have smoother surfaces.