Achieving higher efficiencies with a low-cost etch for in-line-diffused silicon wafer cells

摘要

Emitter formation is one of the most critical processes in the fabrication of silicon wafer solar cells. The process for standard emitter formation adopted in the photovoltaic industry is tube-based diffusion, using phosphorus oxychloride as the dopant source. A potentially low-cost alternative that typically results in lower solar cell efficiencies is in-line diffusion, using phosphoric acid as the dopant source. The Solar Energy Research Institute of Singapore (SERIS) recently developed a technique called the 'SERIS etch, a non-acidic etch-back process technology that provides a controllable, uniform and substantially conformal etch-back suitable for solar cell processing. By using the SERIS etch, efficiencies of up to 18.7% have been demonstrated for homogeneous-emitter silicon wafer cells; a 0.4%_(abs) efficiency improvement has also been achieved for a unique selective-emitter approach exploiting this novel etch. All work was carried out on industrial-grade p-type Cz wafers with conventional screen-printed metallization and a full-area aluminium back-surface field (Al-BSF). With Al local BSF (LBSF) homogeneous-emitter solar cells, efficiencies of 19.0% were achieved using in-line emitter diffusion and the SERIS etch, a 0.7%_(abs) efficiency increase over the baseline efficiency at the time. To the authors' knowledge, these are the highest solar cell efficiencies ever reported for in-line-diffused silicon solar cells. Moreover, the SERIS etch is a cost-effective alternative to generating pyramid-textured surfaces without using conventional metal-assisted silicon-etching processes.