Revani diffusion model in Cu(In,Ga)Se2

Abstract

The commercial attractiveness of Cu(In,Ga) (S,Se)2 (CIGS) photovoltaics is still curtailed by the R&D gap that separates it from silicon. Overcoming the gap requires the pursuit of strategic approaches, leaving plenty of room for R&D at both industrial and lab scale. Yet, its technological progress hinges on our understanding of the diffusion phenomena that occur during and after the absorber growth, particularly in combination with alkali metal doping. This contribution introduces a simplified model of atomic diffusion in CIGS based on insights drawn from recent and older (but crucial) literature. The concept of anisotropy-induced fluctuations emerges. We hypothesize that grain-dependent inhomogeneities arise in CIGS devices because of crystallographic dependent alkali metal diffusivities. Numerical simulations reveal that inhomogeneous doping density and CdS buffer layer thickness may impair the device performance by up to more than 1% absolute efficiency.