Germanium photovoltaic cells with MoOx hole-selective contacts

Abstract

Very thin, thermally evaporated MoOx (x < 3) layer has been used as transparent hole-selective contact on an n-type Germanium substrate to effectively demonstrate PV conversion capability. The fabricated MoOx/Ge heterojunction PV cell shows a photocurrent density of 44.8 mA/cm2 under AM1.5G illumination, which is comparable to that of conventional Ge PV cells. However, a low open-circuit voltage of 138 mV is obtained, which might be explained by the presence of tunnelling mechanisms through the MoOx/Ge interface. To our knowledge, this is the first demonstration of a hole-selective contact made of transition metal oxide on an n-type semiconductor different from c-Si. Thus, this work may have important implications toward the development of new device architectures, such as novel low-cost Ge PV cells with possible applications in multijunction solar cells and thermophotovoltaics.