Etch-back of p+ Structures for Selective Boron Emitters in n-type c-Si Solar Cells

Abstract

In order to minimize electrical losses in the phosphorous emitter being one of the dominant factors limiting the performance of standard screen-printed p-type c-Si solar cells, selective emitter structures have been introduced to advanced standard p-type solar cells in recent years. A selective emitter is expected to yield various benefits for many different kinds of n-type solar cell concepts as well. The technical implementation of such a selective p+ diffused Si region by wet chemical etch-back of the heavily doped Si wafer surface via porous Si (por-Si) formation is developed into a well controllable process using a new etching solution adapted for p+ doped Si layers in respect of their higher concentration of valence band holes. As an initial proof of concept, integrated into 100 μm thin n-type bifacial large-area Si solar cells, the selectively etched-back B emitter yields a VOC gain of 5 mV and an Rshunt increase by a factor of 20.