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.