Use of QSSPC and QSSPL to Monitor Recombination Processes in P-type Silicon Solar Cells

Abstract

This paper reports the use of injection-dependent local ideality factors, obtained from quasi-steady state photoconductance and photoluminescence measurements, to investigate the effects of various cell processing steps on recombination in solar cells, fabricated using boron-doped Czochralski silicon wafers, with an ∼ 100Ω/□ phosphorus-doped emitter and silicon nitride passivation of both surfaces. It is shown that activation of boron-oxygen complexes in the cells by light soaking can impact the pseudo fill factor and is manifest in increased local ideality factors in the injection range between maximum power point and open circuit voltage. The introduced recombination was modeled as a single Shockley Reed Hall (SRH) recombination centre at Ec - Et = 0.41eV and an electron:hole capture cross section ratio of ∼14. The effects of boron and phosphorus laser doping on the injection-dependent local ideality factor were also investigated. Boron laser doping was shown to introduce additional recombination in cells, as indicated by the increased local ideality factor in the injection range between maximum power point and open circuit voltage. However, in this case, the additional recombination was not well-modelled by a single SRH recombination centre, especially in the mid-injection range. Finally, it is shown that high temperature belt furnace anneals can place cells into a specific recombination state, and cells can be returned to this state by subsequent anneals even after additional recombination is introduced into cell by processes like laser doping.