18.7% Efficient inline-diffused screen-printed silicon wafer solar cells with deep homogeneous emitter etch-back

One of the critical fabrication processes of silicon wafer solar cells is the emitter formation. Tube based diffusion, using phosphorus oxychloride as the dopant source, is the standard in the photovoltaic industry. Inline-diffusion, using phosphoric acid as a dopant source, is a potentially low-cost alternative; however it typically results in lower solar cell efficiency. This paper presents an improved etch-back process, 'SERIS etch', for inline-diffused emitters, which achieves batch average efficiency of 18.6% using 156 mm pseudo-square industrial-grade p-type Cz mono-silicon wafers with conventional screen-printed metallisation and aluminium back surface field (Al-BSF). The best cell is 18.7% efficient, with an open-circuit voltage of 631 mV and a fill factor of 80.6%. These high efficiencies were achieved by co-optimisation of the emitter dopant profile and the emitter etch-back process. A variety of characterisation techniques, such as scanning electron microscopy, effective lifetime measurement, dopant profile analyser, photo- and electroluminescence images, and current-voltage (dark and illuminated) measurements were employed in this work.