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 V-oc as a function of the film thickness of molybdenum trioxide (MoO3) buffer layer in the organic solar cells. The open-circuit voltage (V-oc) increased from 0.57 to 0.97 V as the thickness of MoO3 film is increased from 0 to 50 nm in the device structure of indium-tin-oxide (ITO)/MoO3 (x nm)/tetraphenylporphine (10 nm)/C-60 (40 nm)/bathocuproine (10 nm)/Ag (100 nm). The values between V-oc and the ionization potential (I-p) of MoO3 (x nm) on ITO exhibit linear relationship, where the I-p values change from 4.92 to 5.92 eV as they increase from 0 to 50 nm. The enhancement of V-oc 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 V-oc. (c) 2008 American Institute of Physics.