Large-area Cd-free CIGS solar modules with In₂S₃ buffer layer deposited by ALCVD

The development of Cd-free buffer layers by vacuum process for Cu(In,Ga)Se₂ (CIGS) solar modules becomes even more interesting regarding environmental aspects and the implementation in industrial production. This work presents the latest results of CIGS modules with indium sulfide (In₂S₃) as buffer layer deposited by the atomic layer chemical vapour deposition technique. A module efficiency close to 13% was realised on the area of 30×30 cm² (η = 12.9%, V _OC = 27.8 V, FF = 72.6%, I_SC = 0.457 A, aperture area: 714 cm² and 42 cells). Diffusion processes at the buffer layer interfaces, dependent on deposition temperature and post annealing, have been investigated by X-ray photoelectron spectroscopy, secondary ion mass spectrometry and sputtered neutral mass spectrometry analysis. Diffusion of Cu and Na into the buffer layer and intermixing of S and Se at the In ₂S₃/CIGS interface have been detected.