A hybrid resist hemispherical-pit array layer for Light trapping in thin film silicon solar cells via UV nanoimprint lithography

In this paper, we report micromorph tandem solar cells coated with a hemispherical-pit (HP) array layer, which traps light and consequently enhances the efficiency. A quartz mold for ultraviolet nanoimprint lithography (UV-NIL) was fabricated by combining UV photolithography and wet-etching technology, and the HP arrays were then transferred onto the tandem solar cells through UV-NIL. The HP array layer could simultaneously reduce the average reflectance of the tandem solar cells from 7.7% to 1.8%, and effectively enhance light trapping by scattering more incident light into the tandem solar cells. A relative improvement of the efficiency of the tandem solar cells coated with the HP array layer is up to 4.1% as compared to the reference device. The current voltage characteristics of the tandem solar cells as a function of incident angle were also investigated. The power conversion efficiency of the tandem solar cells coated with the HP array layer is always higher than that of the reference with the same incident angle. The results further show that the HP array layer can effectively decrease the reflectance and scatter more incident light into the solar cells at larger angles not only for normal incidence but also for the obliquely incident light. The external quantum efficiency (EQE) of the tandem solar cells coated with the HP array layer was also investigated as well as the reference tandem solar cells. The possible physical mechanism behind the observation is also discussed in this work.