1. 2 New Materials and Concepts for Cells and Modules
Summary / Abstract:
State-of-the-art (semi-)transparent photovoltaic (TPV) devices are mainly focused on the partial absorption of visible spectrum and/or multiple conversion mechanisms of ultraviolet (UV) and/or infrared (IR) spectrum. By selectively absorbing these wavelengths the Shockley–Queisser (SQ) limit for the efficiency of a TPV single junction with 100% average visible transparency is 20.6%, compared to 33.1% for an opaque PV. Focusing on UV-selective harvesting, the area of UV-selective TPV devices is still in a pre-mature stage, but showing promising results in the last few years. To selectively harvest in the UV region, wide bandgap materials are required. Among different families of inorganic materials, oxides excel in stability, abundance, and present typically wide bandgaps. ZnO is a good candidate for being used as an absorber due to its natural n-type conductivity, wide bandgap, optical transparency and excitonic properties. One important issue of this material is the lack of bipolarity due to selfcompensation, which has limited the possibility of obtaining reliable p-type conductivity,  and thus the fabrication of ZnO homojunction devices. NiO is a prototypical p-type oxide that can be used to form a heterojunction with the ZnO absorber, as reported in literature.