Photonic-structured TCO front contacts yielding optical and electrically enhanced thin-film solar cells

Abstract

Wavelength-structured transparent conductive oxide (TCO) electrodes are highly promising to improve both the optical and electrical performance of photovoltaic (PV) devices, due to wave-optical light-trapping (LT) effects and higher TCO volume without increasing optical losses. Herein we present a complete study of the benefits of microstructured IZO contacts applied on amorphous-silicon (a-Si) thin film solar cells. The IZO LT structures were integrated by an innovative colloidal lithography process on the front contact of the cells, resulting in enhancements of 26.7% in photocurrent, with respect to planar reference cells, when using an ultra-thin (30 nm) flat IZO layer between the LT structures and the a-Si absorber. However, the best efficiency enhancement (23.1%) was attained with an optimized thickness of 190 nm for this layer, due to a more favorable combination of optical and electrical gains. In view of the application of this LT strategy in flexible PV devices operating under bending, the angular response of the cells was studied for 0-90° incidence angles. This showed that the LT enhancements are generally higher at oblique incidence, reaching 53.2% and 52%, respectively in photocurrent and efficiency, at ± 70° angles with the optimized flat IZO thickness of 190 nm; and 52.2% in efficiency at ± 40° with the ultra-thin thickness of 30 nm. These results are among the highest gains reported thus far for LT-enhanced thin film solar cells.