Direct fabrication of arrays of Cu(In,Ga)Se2 micro solar cells by sputtering for micro-concentrator photovoltaics

Abstract

Micro-concentrator photovoltaics combines efficiency boosting light concentration with low electrical losses due to thermally cool sub-millimeter sized solar cells. Thin-film Cu(In,Ga)Se2absorber layers do not suffer from edge recombination enabling miniaturization to the micrometer size, which allows for considerable material saving. Cu(In,Ga)Se2micro solar cells have achieved excellent efficiencies under concentrated light, when fabricated by materially-wasteful lithography processes. However, for commercial consideration, material-efficient synthesis approaches are required. In this work, we demonstrate a novel approach to produce arrays of Cu(In,Ga)Se2micro absorber layers through a two-step process, where a Cu-In-Ga precursor layer is sputtered onto a photolithographically structured resist, followed by lift-off and selenization. Our investigation shows a detrimental contamination of the Cu-In-Ga micro-dots by the photoresist. Therefore, we introduce an additional annealing step in inert-gas atmosphere prior to the selenization step, which leads to the formation of electroactive Cu(In,Ga)Se2 micro absorbers. We report the synthesis and characterization of working micro solar cells with an efficiency of 1.2% under 1 Sun. This proof of principle opens up a new material-efficient synthesis route for the direct fabrication of arrays of micro solar cells and puts forward the potential to achieve higher power conversion efficiencies upon further process optimization.