Microcrystalline Si1-xGex solar cells exhibiting enhanced infrared response with reduced absorber thickness

Thin film p-i-n junction solar cells incorporating hydrogenated microcrystalline Si1-x,Ge-x (mu c-Si1-xGex:H) absorber i layers (1 mu m) have been fabricated by plasma-enhanced chemical vapor deposition in the composition range of 0 <= x <= 0.35. By increasing Ge content from x = 0 to 0.15-0.2, short-circuit current density increases by similar to 5mA/cm(2) with spectral sensitivities extending into the infrared wavelengths (>600 nm). However, solar cell parameters for larger Ge contents (x > 0.2) are lowered by the increased charge carrier recombination in the [mu c-Si1-xGex:H i layer. As a result, a 6.3% efficient solar cell is obtained at x = 0.2, exhibiting infrared response even higher than that of double-thickness pc-Si:H solar cells. The solar cell shows excellent performance stability under prolonged light soaking. (C) 2008 The Japan Society of Applied Physics.