How do absorber partner layers like buffer/window layers contribute to photogenerate voltage in a solar cell?
A larger Voc of 900 mV was obtained owing to the larger band gap of a-Si (Eg = 1.7 eV) compared to ~700 mV by c-Si (Eg = 1.12 eV) partner for FeSi2 absorber based solar cell. This leads to a bigger build-in potential [Paper DOI:10.1016/j.tsf.2011.05.030] in the cell. Thus, 200 mV improvement was achieved by a window layer with larger band gap.
What is the scientific reasoning behind this?
FeSi2 is a p-type semiconductor with a bandgap of 0.83-0.87 eV, so when you are using a buffer layer with 1.7 eV it show more Voc because then your absorber can absorb more light in comparison of one with band gap 1.1 eV. In case of 1.1 eV most of the visible range get absorbed by buffer layer only, light can't reach upto the depletion region where usually the generation of e-hole pair happens. If more light get absorbed by buffer layer then it will cause more heating in your device which again reduce efficiency.
FeSi2 is a p-type semiconductor with a bandgap of 0.83-0.87 eV, so when you are using a buffer layer with 1.7 eV it show more Voc because then your absorber can absorb more light in comparison of one with band gap 1.1 eV. In case of 1.1 eV most of the visible range get absorbed by buffer layer only, light can't reach upto the depletion region where usually the generation of e-hole pair happens. If more light get absorbed by buffer layer then it will cause more heating in your device which again reduce efficiency.
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