Angle dependent specular reflectance study on antimony triselenide photovoltaic absorber grown on periodically textured substrates

Abstract

Typical thickness of the absorber layer in conventional thin film photovoltaics is of the order of few microns to few tens of nanometers depending upon the light absorber material used. Optimum values are often associated with the diffusion length of the minority charge carriers, that determine the upper limit and hence the optical absorption coefficient. On the other hand, it is desirable to increase absorption coefficient to maximize the utilization of incident photons. To achieve the same, the optical path length of the incident photons needs to be increased. Surface modifications via random/periodic texturing is considered for light trapping, as it induces multiple reflections of the incident photons, thereby increasing optical path length. In this work, glass substrates were textured with SU-8 2005 photoresist consisting of periodical array of micro cuboids (height ∼6 μm; side length ∼100/70/50/20μm) over an area of 20 mm × 20 mm using i-line lithography. Sb2Se3 absorber layer was conformally grown onto textured as well as on plain substrates via e-beam evaporation. UV–Vis-NIR spectra were recorded and the optical absorbance was analyzed as a function of cuboidal size. Optical absorption increases with decrease in the cuboidal feature size for side lengths up to 40μm and decreased for 20μm. Confirmative angle dependent specular reflectance study was done to correlate the observed absorption behavior, which was in corroboration with absorption measurements. Complementing absorption and reflectance results were understood through COMSOL Multiphysics optical path tracing simulations.