Ultrathin, flexible, hybrid solar cells in sub-ten micrometers single crystal silicon membrane

Recently, free-standing, ultrathin, single crystal silicon (c-Si) membranes have attracted considerable attention as a suitable material for low-cost, mechanically flexible electronics. In this paper, we report a promising ultrathin, flexible, hybrid solar cell based on silicon nanowire (SiNW) arrays and poly (3,4-ethylene-dioxythiophene):polystyrenesulfonate (PEDOT:PSS). The free-standing ultrathin c-Si membranes of different thicknesses were produced by KOH etching of double-side polished Si wafers for various etching times. The processed free-standing silicon membranes were observed to be mechanically flexible and, in spite of their relatively small thickness, the samples tolerated the different steps of solar cell fabrication, including surface nanotexturization, spin casting, dielectric film deposition and metallization. We describe the experimental performance of a promising light trapping scheme in the aforementioned ultrathin c-Si membranes of thicknesses as small as 5.7 μm employing front surface random SiNW texturization in combination with a back-surface distribution of silver (Ag) nanoparticles (NPs). We report the enhancement of both the short circuit current density (J_SC) and the open circuit voltage (V_OC) that has been achieved in the described devices. Such enhancement is attributable to the plasmonic back scattering effect of the back-surface Ag NPs, which led to an overall 10% increase in the power conversion efficiency (PCE) of the devices compared to similar structures without Ag NPs. A PCE in excess of 6.62% has been achieved in the described devices having a c-Si membrane of thickness 8.6 μm. The described device technology could prove crucial in achieving an efficient, low cost, mechanically flexible photovoltaic device in the near future.