The influence of the oxide buffer layer (OBL) on the power conversion efficiency (PCE) in inverted poly (3-hexylthiophene) : fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (P3HT: PCBM) photovoltaic cells was investigated. Three different hole buffer layers (HBLs) of poly (3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS), tungsten-oxide (WO3), or molybdenum-oxide (MoO3) were used to improve the charge generation between the P3HT : PCBM and the Ag electrode. Atomic force microscopy images showed that the surface of the P3HT: PCBM active layer with a MoO3 OBL was smoother that with a PEDOT: PSS layer or a WO3 layer and without a HBL. The PCE of the OPV cells with a MoO3 OBL was higher than those of the inverted OPV cells with a PEDOT: PSS layer or a WO3 layer and without a HBL. The inverted OPV cells containing a MoO3 OBL with a high-work function provided a large interface between the P3HT: PCBM active layer and the Ag electrode due to charge generation, resulting in an enhancement of the device performances for the OPV cells with a MoO3 OBL.

Keywords: Organic photovoltaic cells; Oxide buffer layer; Power conversion efficiency; Inverted structure