Enhanced light trapping in thin-film solar cells by a directionally selective filter

Abstract

A directionally selective multilayer filter is applied to a hydrogenated amorphous silicon solar cell to improve the light trapping. The filter prevents non-absorbed long-wavelength photons from leaving the cell under oblique angles leading to an enhancement of the total optical path length for weakly absorbed light within the device by a factor of kappa(r) = 3.5. Parasitic absorption in the contact layers limits the effective path length improvement for the photovoltaic quantum efficiency to a factor of kappa(EQE) = 1.5. The total short-circuit current density increases by DeltaJ(sc) = 0.2 mAcm(-2) due to the directional selectivity of the Bragg-like filter.

Current Concepts for Optical Path Enhancement in Solar Cells

“…The highest enhancement reported in applying a resonant light trapping scheme has been achieved by the Kimmerling group with α EQE = 135 (indicated by the red circle n of the absorber material for circumsolar irradiation (Θ C ). The corresponding circles indicate the highest experimentally achieved enhancement found in literature so far [11,38,49].…”

“…Nevertheless, promising attempts have been conducted by Höhn et al [48]. A comprehensive overview on the effects of different angular selective structures on silicon solar cells has been given by Ulbrich et al [43,49] and is also described in Chapter 7 of this book.…”

“…For the experimental implementation of angular-selective structures, feasible concepts of integration into a solar cell are still lacking. Nevertheless, angular-selective light trapping structures hold the largest theoretical upper limit for enhancement and the first promising results have been achieved [49].…”

Light‐Trapping in Solar Cells by Directionally Selective Filters

“…Light-trapping schemes that bear an unintentional angular selectivity may still enable a high annual yield provided the angular restrictions are relatively wide or they are limited to a certain range of photon energies [36]. For the untracked systems the tolerance for spectral and angular selectivity increases for thinner cells.…”

“…Nonetheless, the effect of an angle restriction was successfully shown in experiments that prove a current increase by the improved light-trapping [36,37].…”