Benefit of textured CIGS cells for low reflecting nanogrid application

Abstract

We show the results of nanotextured device designs combined with carefully placed nanogrids in order to minimize optical losses. Finite element method (FEM) based optical modeling indicates that the reflection of both the layer stack and the metal is diminished by the proposed configuration in which the metallic nanowires at the front of a device are placed into the relatively shallow crevices, whereby the metal is not covered by other materials of the cell stack. The electric field distribution and energy dissipation (i.e. absorption) diagrams of the texture show how the light is distributed and where it is absorbed. It shows that light is ‘concentrated’ in the tips of the texture (depending on the size and wavelength of the light). Simultaneously, for wavelengths above 750 nm there appears to be a reduction of the E-field in the lower part of the texture and, therefore, putting a metallic nanowire in this position has hardly any negative optical effect.

Furthermore, the impact of the texture height up to 1000 nm and the nanowire width up to 150nm was systematically investigated for a texture and wire period of 500 nm. The spectra reveal dimension dependent and wavelength specific optical features. This is the case even if the flat nanowire remains fully exposed to the front glass medium (i.e. not embedded underneath absorbers). At a texture height of 900 nm, the reflection related current loss is reduced by an order of magnitude compared to flat layer stacks, virtually regardless of the width of the metal nanowire. This opens up exciting new ways of creating nano-metal containing devices without the usual optical losses.