Simulation of ultra-thin solar cells beyond the semi-classical bulk picture

We discuss the photovoltaic characteristics of ultrathin GaAs solar cells as simulated using the standard semi-classical drift-diffusion-Poisson model and an advanced microscopic quantum-kinetic approach based on the nonequilibrium Green's function formalism. In the case where the semi-classical model relies on the conventional assumption of flat-band bulk absorption coefficients, substantial qualitative and quantitative discrepancies are found. The agreement between classical and quantum kinetic approaches is improved by consideration of field-dependent absorption and emission coefficients in the semi-classical approach, which underlines the strong impact of the large built-in potential gradients on absorption and emission in ultra-thin solar cell architectures. In addition, our findings concerning the effects of non-classical regions induced by blocking layers at carrier selective contacts are briefly summarized.