| Summary: | We have combined recent experimental developments in our laboratory with modelling to
devise ways of maximising the stabilised efficiency of hydrogenated amorphous silicon
(a-Si:H) PIN solar cells. The cells were fabricated using the conventional plasma enhanced
chemical vapour deposition (PECVD) technique at various temperatures, pressures and gas
flow ratios. A detailed electrical-optical simulator was used to examine the effect of
using wide band gap P-and N-doped μc-SiOx:H layers, as well as a
MgF2
anti-reflection coating (ARC) on cell performance. We find that with the best quality
a-Si:H so far produced in our laboratory and optimised deposition parameters for the
corresponding solar cell, we could not attain a 10% stabilised efficiency due to the high
stabilised defect density of a-Si:H, although this landmark has been achieved in some
laboratories. On the other hand, a close cousin of a-Si:H, hydrogenated polymorphous
silicon (pm-Si:H), a nano-structured silicon thin film produced by PECVD under conditions
close to powder formation, has been developed in our laboratory. This material has been
shown to have a lower initial and stabilised defect density as well as higher hole
mobility than a-Si:H. Modelling indicates that it is possible to attain stabilised
efficiencies of 12% when pm-Si:H is incorporated in a solar cell, deposited in a NIP
configuration to reduce the P/I interface defects and combined with P- and N-doped
μc-SiOx:H layers and a MgF2 ARC.
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