Impact of buffer and absorber properties in the vicinity of the interface on wide-gap Cu(In,Ga)Se2 solar cell performance

One of the main reasons for the V_oc deficit in Cu(In,Ga)Se₂ (CIGS) solar cells with a wide band gap is often attributed to interface recombination, which is a consequence of the defective heterointerface and encouraged by the non-ideal band alignment between the absorber and the CdS layer. Although a highly defective heterointerface is likely not avoidable, some properties of the buffer layer and the absorber material in the vicinity of the interface could decrease the recombination losses. Compositional variations in CIGS can result in a band gap increase at the absorber/buffer interface and type inversion in the absorber layer. Simulations predict the optimal depth of type inversion on wide band gap CIGS devices and the magnitude of device performance increase that can be expected from such structures. In addition, the benefit of the decreased thickness and increased doping of the buffer layer is calculated. The results are compared with a “standard” 1.15-eV CIGS device, where the benefits of such variations are significantly smaller.