Si-nanocrystals embedded in SiNWs to reduce thermalisation in solar cells

Abstract

Despite their interesting efficiencies and stabilities, first and second generations solar cells suffer from thermalisation that reduces the photovoltaic performances under operating conditions. In third generation solar cells scenarios, the use of Nano-Crystals (NCs) with suitable dimensions can be a realistic alternative to overcome the thermalisation phenomena. Due to the quantum confinement, silicon NCs with sizes less than 5 nm could be an efficient tool for down conversion and/or carriers multiplication by converting high energy photons (UV) to visible ones via photoluminescence (PL).This paper gives interesting results by stacking silicon NCs in Silicon NanoWires (SiNWs) which are elaborated at the top of a silicon pn homo-junction. NCs are obtained by annealing an amorphous silicon layer deposited on the SiNWs layer. Room temperature photoluminescence measurement at an incident wavelength of 250 nm shows three PL peaks at 378 nm, 480 nm and 587 nm. The latter is attributed to silicon NCs. Furthermore, the photovoltaic efficiency is considerably enhanced by an amount of 36.3 % from 6.9 % to 9.4 % which is due to an important enhancement of 30.3 % in the absolute value of the short-circuit current density values in presence of Si-NCs. We discuss these results with regard to the physical characterizations performed on fabricated samples.