Lightwave trapping in thin film solar cells with improved photonic-structured front contacts

Abstract

Photonic microstructures placed at the topside of photovoltaic cells are currently one of the preferred light management solutions to obtain efficiency enhancement due to the increment of the optical absorption produced in the active medium of the devices. Herein, we present the results concerning a practical, low-cost and scalable approach to integrate metal-oxide based light trapping microstructures on the front contact of amorphous silicon thin film solar cells. A colloidal lithography method was used to pattern the wavelength-sized pyramidal-like features composing the structures, made of two different transparent materials, TiO₂ and IZO, allowing the detailed study of the influence of their geometrical parameters on the optoelectronic properties of the devices. These top coating structures are deposited as a post-process after the solar cell fabrication, thus facilitating and broadening their industrial applicability. Measurements of the light absorption, external quantum efficiency and I–V curves revealed that the structured coatings provide strong broadband improvements in the generated current, due to the suppression of reflected light at short wavelengths and the increment of the optical path length of the longer wavelengths (via light scattering), within the amorphous silicon layer. As a result, in the four types of structures analyzed in this study, remarkable increments were achieved in the cells’ efficiencies (up to 14.4%) and generated currents (up to 21.5%), with respect to the flat reference cells.