Structure of silicon-based thin film solar cell materials: annual technical progress report, 1 April 2002-31 August 2003

OCLC Number: 55668663 Excerpt: ... features are also similar to those from the earlier films. The lack of improvement in microstructure is correlated with a lack of improvement in the photoresponse found to date with such hydrogen-diluted material. SAXS Study of USSC Microcrystalline Solar Cell Materials Three microcrystalline-Si:H films were provided by USSC. They were fabricated with three different techniques: RF-, VHF-, and microwave-PECVD. These produce increasing deposition rates. Both SAXS and flotation density measurements were completed. Tilting SAXS was done to look for oriented microstructure. The intensities are high from all three and show slightly different shapes, indicating different size distributions of scattering objects. All three have some oriented microstructure but it is more significant in the RF and VHF samples. SAXS intensities increase systematically with deposition rate implying more heterogeneity with increasing rate. Flotation densities are quite high ( similar to void-free a-Si:H ), probably due to lower bonded H contents in these microcrystalline films. SAXS Study of KAIST Photo-CVD a-Si:H Films At the request of a group in the Department of Electrical Engineering and Computer Science of the Korea Advanced Institute of Science and Technology ( KAIST ), we have analyzed a series of a-Si:H films prepared by photo-CVD. The focus was on the transition from protocrystalline to the mixed amorphous / microcrystalline regime and hydrogen dilution was the variable in the series. They had postulated that there was an increase in microvoids in the protocrystalline regime prior to microcrystallite formation. However, the SAXS intensities remained extremely low until microcrystallites were detected by XRD, after which the intensities became strong. The films in the protocrystalline regime are very homogeneous and similar in structural quality with the best films we have analyzed that were grown by PECVD and HWCVD. Thus, their postulate rega...