MISTiCal · Semi-Transparent Micro-Striped Chalcopyrite Cu(In,Ga)Se2 solar cells for window applications

While a variety of building-integrated photovoltaics (BIPV) solutions is emerging, with conventional photovoltaic systems already installed on roofs and facades, many modern buildings consist of large areas of windows, which represent an available surface to implement semi-transparent photovoltaic (STPV) modules. Their implementation will permit the production of electricity, and its immediate consumption for the end-user, without problem of transport and eventual loss. Moreover, it will contribute to a better energy autonomy and independency.The MISTiCal project aims to establish efficient semi-transparent solar cells for window applications by developing a novel micro-structured architecture for Cu(In,Ga)Se2 (CIGS) thin-film photovoltaics and the respective fabrication processes. Using CIGS micro-stripes with a width of ~200 micrometers, they are below the resolution of the human eye at a viewing distance above 70 cm, making the window fully transparent to natural daylight. Comparing to other STPV technologies, such as silicon, dye-sensitized (DSSC), organic solar cells (OPV), or ultra-thin CIGS, the micro-structured CIGS STPV presents a good alternative with several strengths such as its industrial maturity and its competitive cost with Si-based solar modules, high efficiency, stability and good aesthetics.The objectives of the MISTiCal project will be (1) to optimize the CIGS device stack for the semi-transparent property, (2) to optimize the micro-structuring of CIGS to demonstrate semi-transparent solar cells, and (3) to assess the performance and the bifacial functionality of the solar cells. The overall goal is to demonstrate a power conversion efficiency of 8% at an average visible transmittance (AVT) of 50%, surpassing the present state of the art for STPV.