Limitation of Industrial Phosphorus-diffused Emitters by SRH Recombination

Abstract

It is commonly assumed in the PV community that Auger recombination is the dominant loss mechanism in heavily phosphorus-doped emitters of industrial Si solar cells. Contrary to this assumption, we show in this work that most of the losses are caused by Shockley-Read-Hall (SRH) recombination via defect states introduced by inactive phosphorus. Using numerical device simulations, we successfully reproduce all the measured J0e values of a series of profiles (with various concentrations of inactive phosphorus) with an effective SRH capture crosses-section for holes, σp = 7.5×10-18 cm2. The composition of inactive phosphorus (e.g. in form of clusters of interstitial phosphorus, fine and rod-shaped precipitates) may vary under different fabrication conditions, hence we do not claim that this σp value is globally valid. However, because the series of profiles is representative for many emitters in mass production, our result implies generally higher SRH than Auger recombination rates and has decisive implications on the improvement of such industrial emitters: many emitters have not yet reached the Auger-limit and they may still be significantly improved by reducing their density of inactive phosphorus.