CD-free Cu(In,Ga)Se₂ thin-film solar modules with In₂S₃ buffer layer by ALCVD

The atomic layer chemical vapour deposition (ALCVD) technique allows the deposition of highly homogeneous thin-films with an excellent step coverage. This method has already shown promising results for the deposition of cadmium-free buffer layers in Cu(In,Ga)Se₂ (CIGS) thin-film solar cells (13.5% efficiency with indium sulphide buffer). In this work, the process has been up-scaled to module areas of up to 30 × 30 cm². The indium sulphide buffer layer was deposited at substrate temperatures between 160 and 220 °C using indium acetylacetonate and hydrogen sulphide precursors. An efficiency of η = 10.8% (open-circuit voltage, V_OC = 592 mV; fill factor, FF = 62%; current density, j_SC = 29.5 mA/cm²) for a module area of 30 × 30 cm² has been achieved. For laboratory cells even an efficiency of 14.9% was realised. Damp heat stability testing of CIGS mini-modules indicates a similar behaviour of both devices with ALCVD indium sulphide and solution grown cadmium-sulphide buffer layer.