Independent control of open-circuit voltage of organic solar cells by changing film thickness of MoO3 buffer layer

The authors report the systematic control of Voc as a function of the film thickness of molybdenum trioxide (MoO3) buffer layer in the organic solar cells. The open-circuit voltage (Voc) increased from 0.57to0.97V as the thickness of MoO3 film is increased from 0to50nm in the device structure of indium-tin-oxide (ITO)∕MoO3 (xnm)/tetraphenylporphine (10nm)∕C60 (40nm)/bathocuproine (10nm)∕Ag (100nm). The values between Voc and the ionization potential (Ip) of MoO3 (xnm) on ITO exhibit linear relationship, where the Ip values change from 4.92to5.92eV as they increase from 0to50nm. The enhancement of Voc was achieved without affecting short-circuit current density and fill factor. Consequently, the power conversion efficiency of the device increases from 1.24% to 1.88% primarily due to the increase in Voc.