Large area and low-cost nanoholes-based plasmonic back reflector fabricated by a simple nanofabrication technique for photovoltaics applications

Plasmonic back reflectors (PBRs) are employed in thin film and ultra-thin film solar cells to increase their optical thickness and energy conversion efficiency. Here, we report a wet-chemical etching based nanofabrication technique to prepare large area and low-cost nanoholes-based plasmonic back reflectors (n-PBRs). The n-PBR is a 150 nm thick Ag thin film embedded with random nanoholes with varying structure and morphology. We successfully incorporated the n-PBR into a standard a-Si:H thin film solar cell built on a randomly textured FTO substrate; the textured FTO serves as both the front contact and light-entry side light trapping medium. Three n-PBRs each with different density of random nanoholes were studied. All the plasmonic a-Si:H solar cells with n-PBRs exhibited an optical absorption enhancement in the spectrally intense 550–800 nm wavelength range with an overall enhancement factor of 1.1 and a maximum enhancement factor of 1.3 in the 720–780 nm wavelength range. The n-PBRs produced a haze of 65% in the 700–800 wavelength range. The hazy back contact effectively scatters the unabsorbed light back into the active medium of the solar cell with increased path length and hence, contributes to the enhanced absorption in the solar cell. The method of nanofabrication reported here to produce plasmonic back reflectors can be easily adopted into commercial fabrication of various types of solar cells including ultrathin inorganic and organic, polymer, perovskite and dye-sensitized solar cells to enhance their energy conversion efficiency without adding any cost/watt to the solar cells.