Solid-state selenization of printed Cu(In,Ga)S2 nanocrystal layer and its impact on solar cell performance

•Soild state selenization of nanocrystal ink by using elemental Se.•The selenized film showed a double layer microstructure.•The selenization with higher Se supply increased the thickness of the recrystallized layer.•However, solar cell performance was not proportional to the thickness of the recrystallized layer.•Copper sulfoselenide found at the boundary might promote the conversion of sulfide into selenide.

Cu(In,Ga)S2nanopowder was printed on Mo-coated sodalime glass substrates and selenized from a Se-coated cover glass. The selenized Cu(In,Ga)(Se,S)2 film consisted of three layers with a different morphologies and micro-structures. Although the top layer showed large grains recrystallized from nanocrystals, the bottom layer was almost identical to the original precursor. The middle layer, as a thin boundary layer was found to be a mixture of carbon and Cu sulfoselenide. At a higher Se thickness (>1.2 μm), a lower fill factor and short circuit current density were obtained, which might result from the accumulation of a Cu secondary phase. The solar cell, which consisted of Al2O3:ZnO/i-ZnO/CdS/Cu(In,Ga)(S,Se)/Mo/glass using the selenized absorber, showed the following properties: efficiency=8.28%, Jsc=26.14 mA/cm2, Voc=0.483 V, and fill factor=65.58% for AMG1.5 at 25 °C.