Novel non-metallic non-acidic approach to generate sub-wavelength surface structures for inline-diffused multicrystalline silicon wafer solar cells

One of the main restrictions on further enhancement of the multicrystalline silicon (multi-Si) wafer solar cell efficiency is the high reflectance loss from the front surface. Double-texturing, including a microtexturing by conventional isotropic acidic-texturing followed by nano-texturing using sub-wavelength structures (SWS), provides a possibility to remove this limitation. However, presently available doubletexturing processes involve multiple and high-cost nano-texturing process steps and thus have not become industrially viable. This study presents an improved double-texturing process and reports its successful implementation using low-cost inline-diffusion and non-acidic 'SERIS etch' etch-back technology. The process is based on reactive ion etching (RIE) as a metal-free nano-texturing step, along with the conventional acidic iso-texturing process. The process is optimised based on effective minority carrier lifetime and weighted average reflectance (WAR) measurements, on 156 x 156 mm2, industrial-grade, ptype multi-Si wafers. This optimised double-textured SWS surface has a WAR of 3.2% after silicon nitride deposition, which is significantly lower than that of conventional acidic iso-textured wafers (WAR of 6-7%). However, this optimised surface maintains the same values of the effective minority carrier lifetime as for the reference conventional acidic-textured multi-Si wafers. The optimised nano-texturing recipe is also successfully applied to alkaline-textured monocrystalline silicon wafers. (C) 2014 Elsevier B.V. All rights reserved.