Effects of thermal treatment on micro-Cu(In,Ga)Se₂ solar cells prepared by one-stage selenization of sputter Cu-In-Ga precursor

Micro-concentrator photovoltaics combine sub-millimeter scale solar cells with optical concentrator systems, enabling higher power conversion efficiencies, material savings, and improved heat management. In this work, we investigated the effects of thermal treatment of Cu-In-Ga precursors on Cu(In,Ga)Se 2 micro solar cells. The devices were fabricated by sputtering a Cu-In-Ga precursor onto a soda-lime glass/SiO x N y /Mo/SiO x pre-structured substrate with micro-holes of 200 and 250 µm diameter, defined by photolithography. The precursor undergoes thermal treatment at 450 °C, followed by selenization at 480°C. The treated Cu-In-Ga exhibited a smoother surface, with indistinct grains, compared to the as-deposited film. However, areas of exposed Mo were observed upon treatment. After selenization, the treated micro-absorber exhibited improved elemental composition with Cu to (Ga+In) ratio of 0.81±0.06, compared to 0.76±0.13 for the untreated micro-absorber. Electrical characterization of the devices revealed better overall performance for the treated Cu(In,Ga)Se 2 micro solar cells, with an average Voc of (239±26) mV, significantly higher than the (176±25) mV achieved by untreated micro cells.