Effects of CdS buffer layers on photoluminescence properties of Cu(In,Ga)Se2 solar cells

Photoluminescence (PL) have been studied on Cu(In,Ga)Se2 (CIGS) thin films, CdS/CIGS and CIGS solar cells, to clarify the carrier recombination process. The chemical-bath deposition (CBD) of the CdS buffer layer on the CIGS thin film leads to (i) the enhancement of near-band-edge PL intensity by a factor of 2–3, (ii) change in energy of the defect-related PL and (iii) the slight change in the decay time. They are related not only to the minimization of the surface recombination but also to the modification of native defects at the Cu-poor surface of CIGS by the occupation of Cd atom at the Cu site. A donor–acceptor pair PL at low-temperature and temperature-dependent PL have been studied. They are discussed in terms of the impurity and defect levels created in the CIGS film during the CBD-CdS process.