The etchback selective emitter technology and its application to multicrystalline silicon

Abstract

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 [1, 2]. 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 j0E 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.

Significant minority carrier lifetime improvement in red edge zone in n-type multicrystalline silicon

“…The time needed for an effective co-gettering could be noticeably reduced compared to plain BDG. [36] Obviously, if the etch back method [37] is used to form the emitter, it is possible to use high dopant concentrations and, in principal, separately optimize the gettering efficiency and the doping profile.…”

Non-Vacuum Process for Production of Crystalline Silicon Solar Cells

“…There are various techniques and applications to form selective emitter structures [48]. Double-diffusion with masking [49,50], selective diffusion barrier process [51], oxide masking process and etch back [45,52], implantation process [53] are among these techniques. Depending on the technique, need of laser ablation, additional steps like masking, repeated diffusions, etch back processes are among the drawbacks of such techniques.…”

0.4% absolute efficiency increase for inline-diffused screen-printed multicrystalline silicon wafer solar cells by non-acidic deep emitter etch-back

“…In the case of mono-Si wafer solar cells, Book et al [18] were unable to maintain the integrity of pyramidal shape after an etch-back as portions of the tips of the pyramids were etched during their acidic etch-back process. On the other hand, Basu et al [7,[19][20][21] showed that the 'SERIS etch' was able to maintain the integrity of surface pyramids even for deep etch-backs.…”

“…All the processes mentioned up to now only enable relatively shallow homogeneous emitter etch-backs of up to 10 Ω/sq. The main problem associated with deeper etch-backs is that they are typically not very conformal and thus reflectance from the emitter surface increases after a deeper etch-back [18]. Consequently the potential of the etch-back processes is limited.…”