Effect of germanium fraction on the effective minority carrier lifetime in thin film amorphous-Si/crystalline-Si1xGex/crystalline-Si heterojunction solar cells

摘要

The effect of germanium fraction on the effective minority carrier lifetime (τeff ) for epitaxial Si1-x Ge x layers is extracted using measurements on amorphous(a) Si(n+)/crystalline(c)-Si1-x Ge x(p)/crystalline(c)-Si(p+) heterojunction solar cells with x = 0.25, 0.41 and 0.56. The τeff extracted for Si0.75 Ge 0.25 is ～1 μs, decreasing to ～ 40 ns for Si0.44 Ge 0.56. In addition, the band-gap voltage offset (Woc) increases from 0.5 eV for Si to 0.65 eV for 56% Ge indicating an increase in non-radiative recombination consistent with the reduction in effective lifetime.