Optical characterization and modeling of Cu(In,Ga)(Se,S)2 solar cells with spectroscopic ellipsometry and coherent numerical simulation

Simulations of photovoltaic devices provide a promising tool for the exploration of internal loss mechanisms and assessment of optimization potentials. The knowledge of the internal wave propagation and local photon absorption rate is a fundamental prerequisite for modeling Cu(In,Ga)(Se,S)2 thin film solar cells by means of a sophisticated Technology Computer Aided Design (TCAD) device simulator. In a first step, we applied variable-angle spectroscopic ellipsometry to derive the optical constants of the involved layers, namely the doped and undoped zinc oxide, the In2S3 buffer, the MoSe2 and the molybdenum film. These data enter for a semi-coherent calculation of the wave propagation and of the local generation rate in the thin film stack. Scattering effects due to interface roughness were considered appropriately and the TCAD-simulated photogeneration and reflection spectra were compared with measured quantum efficiencies and reflection spectra, respectively.

► We investigated Cu(In,Ga)(Se,S)2 solar cells optically by spectroscopic ellipsometry.
► We found optical constants data for investigated thin film layers.
► We modeled and simulated the device to identify loss mechanisms.
► Optical losses in window layers and electrical losses in CIGSSe were discussed.
► Photo current gain from In2S3 buffer layer could be identified and quantified.