Modelling Supported Design of Light Management Structures in Ultra-Thin Cigs Photovoltaic Devices

Abstract

Chalcopyrite solar cells exhibit one of the highest conversion efficiencies among thin-film solar cell technologies (> 23.3%), however a considerably thick absorber ≥1.8 μm is required for an efficient absorption of the long-wavelength light and collection of charge carriers. In order to minimize the material consumption and to accelerate the fabrication process, further thinning down of the absorber layer is important. Using a thin absorber layer results in a highly reduced photocurrent density and to compensate for it an effective light management needs to be introduced. Experimentally supported, advanced optical simulations in a PV module configuration, i.e. solar cell structure including the encapsulation and front glass are employed to design solutions to increase the short current density of devices with ultra-thin (500 nm) absorbers. In particular (i) highly reflective metal back reflector (BR), (ii) internal nano-textures and (iii) external textures by applying a light management (LM) foil are investigated by simulations. Experimental verification of simulation results is presented for the external texture case. In the scope of this contribution we show that any individual aforementioned approach is not sufficient to compensate for the short circuit current drop of the thin CIGS, but only a combination of highly reflective back contact and introduction of textures (internal or external) is able to compensate and also to exceed (by more than 5 % for internal texture) photocurrent density of a thick (1800 nm) CIGS absorber.