Wide Band Gap Solar Cells with High Stabilized Performance: Annual Technical Report, 15 July 1995 - 15 July 1996

This report describes work done in Phase II of this subcontract. In their work on materials stability, researchers found that a-Si:H films deposited with H2-dilution of SiH4 gas not only show lower defect densities in the annealed state than the a-Si:H films prepared with pure SiH4, but also better stability against light soaking. The improvement in material stability is found to translatedirectly into an improvement in device quality. In other work, researchers demonstrated that, while in the annealed state a-Si1-xCx:H i-layers prepared with H2-dilution of source gases (i.e., SiH4 + CH4) exhibit similar photoconductive properties to those of H2-diluted a-Si:H materials, the gains made through H2-dilution are largely lost in the degraded state. In investigations of the dependenceof p-i-n solar cell performance, they found that the open-circuit voltage of the cell increases at lower i-layer deposition temperatures as the bandgap of the i-layer is widened, and such an increase is more profound in cells prepared with H2-diluted i-layers. Another area of work is discussed in which researchers developed novel wide gap amorphous and microcrystalline p-layers prepared usingH2-diluted and undiluted mixtures of SiH4, CH4, and B(CH3)3 (TMB) that are to be incorporated as the top layer in the n-i-p solar cell configuration. In their work on solar cell interfaces, they discuss their extended studies of the p/i interface to small sub-monolayer level discontinuities observed in the real-time ellipsometry trajectories for interfaces formed with TMB p-layers. Finally, theydiscuss their new approach to device modeling that is less ambitious than originally proposed because of the absence of reliable input parameters. In this approach, the modeling of solar cell structures is carried out first to establish material parameters that are self-consistent with those derived in detailed studies on intrinsic material thin films.