The deposition of amorphous hydrogenated silicon (a-Si:H) by mercury-sensitized photochemical vapor deposition (photo-CVD) of disilane is reviewed. Depth profiling of the hydrogen in photo-CVD a-Si:H was performed using the nuclear reaction technique, revealing about 12 at.% H in the bulk rising to 18 at.% in the first-deposited layers. The gradation is believed to result from incomplete suppression of window deposition by the perfluoropolyether window coating. Hydrogen evolution studies on photo-CVD a-Si:H show no evidence of a low temperature evolution peak. High efficiency p-it-i-n solar cell structures are discussed, where it is a graded-affinity transitional i layer whose use results in an increased open-circuit voltage Voc. Single-junction solar cell efficiencies of 8.6% and 4.5% are reported for a-Si:H and a-SiGe:H alloys respectively, and preliminary data are presented on a-Si:H/a-SiGe:H tandem cells. The stability of photo-CVD and r.f. glow discharge a-Si:H i layers and p-i-n devices are compared using electron spin resonance measurements, accelerated light soaking techniques and thermal annealing. For the first time, an observable difference between glow discharge and photo-CVD a-Si:H is demonstrated.
All Science Journal Classification (ASJC) codes