Beyond 20% World Record Efficiency for Thin-Film Solar Modules

Abstract

We report on crossing the 20% efficiency line for thin-film solar modules. The efficiency of our cadmium-free Cu(In,Ga)(S,Se)2 (CIGSSe) mid-sized modules (30 × 30 cm2) based on the cost-efficient AVANCIS stacked elemental layer - rapid thermal processing absorber process has evolved in the last two years reaching 19.6%, 19.8% and recently we have achieved an efficiency level of 20.3% as independently measured by NREL. The recent improvements were made possible by thorough variations in absorber composition and elemental distribution. The optimization of the absorber thickness, and of the band gap profile through the engineering of sulfur content and gradient at the absorber surface induces an improved absorber quality leading to a distinct increase in the product of short circuit current density and open circuit voltage (JSC × VOC). Moreover, improving the absorber homogeneity and adjusting the absorber-buffer interface play an important role in enhancing the fill factor.