Comparison of conventional and inverted organic photovoltaic devices with controlled illumination area and extraction layers

Abstract

The impact of device architecture on organic photovoltaic device performance has been problematic to quantify due to extraction layer materials and device testing issues. In particular, published reports have used different pairs of hole and electron extraction layer materials for conventional versus inverted devices. The origins of the large apparent discrepancy in device J–V characteristics become difficult to understand, arising from differences in built-in potentials and in the extraction layers’ conductivities that can affect collection of stray current outside of device area. Here, we show that by using an identical pair of hole and electron extraction layers, and by precisely defining illuminated device area with a shadow mask, most of the differences in the performance of conventional and inverted P3HT:PCBM organic photovoltaic devices are eliminated. The remaining difference in short-circuit current density and EQE spectral shape can be explained primarily by the ratio of hole and electron mobility that leads to more efficient carrier extraction in the inverted devices, with a minor contribution from unintentional p-type doping of the active layer that influences the drift field profile.