The etchback selective emitter technology and its application to multicrystalline silicon

We have developed a simple and industrially applicable selective emitter cell process using only one diffusion step and an emitter etchback to create the high sheet resistance emitter. The process generates a deeper doping profile with a lower surface phosphorous concentration than a directly diffused emitter with the same sheet resistance. This results in an extremely low emitter saturation current j_0E even at a moderate sheet resistance of 60-80 Ω/□. The highest independently confirmed cell efficiency on Cz-Si (146 cm²) was 18.7%. In this work the etching behavior of the acidic solution at the grain boundaries is studied by SEM imaging and high resolution LBIC measurements at 405 nm wavelength. The etchback also leads to a change in reflectivity, which is quantified by reflectance measurements. We furthermore investigate the influence of the base material quality on the gain that can be achieved by this process. Large area solar cells have been processed from solar grade and UMG mc silicon.