Increasing solar energy conversion efficiency in thin film hydrogenated amorphous silicon solar cells with patterned plasmonic silver nano-disk array.

摘要

Thin film hydrogenated amorphous silicon (a-Si:H) solar photovoltaic (PV) cells are inexpensive and have the fastest energy payback time, however, they suffer from light-induced degradation in performance termed as the Staebler-Wronski effect (SWE). Recent advances in the field of plasmonics have revealed the ability of metallic nanostructures to provide polarization independent, wide angle and broadband absorption for ultrathin active absorbing layers (<100 nm). We investigated a two-dimensional array of multi-resonant plasmonic nano-disk structures to improve the optical absorption in the active absorbing layer of a-Si:H PV cells and to compensate for the negative effects of SWE. This nano-disk patterned solar cell (NDPSC) was found to be superior in performance over a commercial thin film a-Si:H reference PV cell by 18.51% for total optical absorption and by 19.65% in short-circuit current density (JSC).;To maximize the optical enhancement in the NDPSC structures, ultra-thin transparent conducting oxide (TCOs) films with high transmittance and low resistivity are desired. We theoretically investigated the ultra-thin (< 50nm) TCO films of different materials and thickness to ascertain their potential employment in plasmonic-enhanced a-Si:H PV devices. We further numerically evaluated the performance of NDPSC structures for experimentally optimized (by our collaborators) ultra-thin TCO films of indium tin oxide (ITO) having high transmittance and low resistivity. We found a 21% enhancement in optical absorption in the active layer of NDPSC structures using a 36nm high quality ITO films.;The plasmonic nanostructures employed for improving optical absorption in solar PV cell applications are not lossless, and suffer from Ohmic losses. We developed a novel technique of exchanging undesired Ohmic losses in metals with useful absorption in the active semiconducting layers in plasmonic-enhanced PV cells. This technique requires the tailoring of geometric skin depth of metals and engaging the inherent absorbance characteristics of the semiconductors. We have demonstrated that between 75%-95% absorbance can be achieved in the semiconducting layers using this technique.