Quantification of Void Defects on PERC Solar Cell Rear Contacts

Passivated emitter and rear (PERC) solar cells can show void formation within their metallized local rear contact. It is known that voids can cause enhanced rear side recombination. In this work, we present a study on void related current losses and the correlation to the local Al-doped silicon layer which forms the back-surface field (BSF) at the rear contact. At first, void related current losses have been quantitatively evaluated. By further microstructural investigation at lengthwise prepared rear contacts, a method for the analysis of BSF thickness distribution was developed. It turned out that BSFs within voids can vanish on both, small and large length scales. Regions with voids can be well passivated and result therefore in negligible current losses. The presented approach allows the quantitatively assessment of PERC solar cell rear contacts in terms of total current losses and void ratio.