Low-cost and low-temperature chemical oxide passivation process for large area single crystalline silicon solar cells

Although thermally grown silicon dioxide is an excellent surface passivation layer for Si wafers, its industrial applicability for solar cell surface passivation is limited due to low throughput and high cost. This has prompted the exploration of low temperature and chemical silicon dioxide processes for silicon solar cells. In this work, a low-cost, low-temperature (40 °C), non-acidic and safe chemical oxide passivation process (named as NCPRE-oxide) with only sodium hypochlorite (NaOCl) solution is proposed and investigated on large area wafers (125 mm × 125 mm). This process uses a single-component chemical solution to grow ultra-thin silicon oxide (SiOx) layer of thickness of about 1.5 nm. The chemical SiOx layer capped with hydrogenated amorphous silicon nitride (SiNx:H) improves passivation on the n-type silicon surface. A considerable enhancement in the effective minority carrier lifetime (τeff) is observed for SiNx:H/SiOx stack on the phosphorous diffused pyramidal textured silicon surface. The versatility of the NCPRE-oxide is verified by transmission electron microscopy, ellipsometry, X-ray photoelectron spectroscopy, effective minority carrier lifetime and photoluminescence imaging measurements. The introduction of present SiNx:H/SiOx stack in our baseline cell fabrication process resulted in the improvement in cell efficiency by 0.3% (absolute) for screen-printed full area aluminum back surface field cells.