期刊
IEEE JOURNAL OF PHOTOVOLTAICS
卷 7, 期 2, 页码 421-429出版社
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/JPHOTOV.2016.2646421
关键词
Annealing; defects; hydrogenated amorphous silicon (a-Si:H); nanostructure; vacancies
资金
- ADEM, A green Deal in Energy Materials of the Ministry of Economic Affairs of The Netherlands
- STW Vidi project from the Delft University of Technology
The nanostructure of hydrogenated amorphous silicon (a-Si: H) is studied by means of doppler broadening positron annihilation spectroscopy (DB-PAS) and Fourier transform infrared (FTIR) spectroscopy. The evolution of open volume deficiencies is monitored during annealing, demonstrating that small vacancies and other small vacancy clusters that are initially present in the a-Si: H nanostructure agglomerate into larger vacancy clusters. The migration of open volume deficiencies is less pronounced for a-Si: H deposited at higher hydrogen-to-silane gas flow rate ratio, R. FTIR spectroscopy reveals the presence of a peculiar peak in the refractive index in the infrared-and hence the calculated mass density-which occurs just before H effusion from the films starts. The combined results of DB-PAS and FTIR spectroscopy indicate that a stress buildup caused by the accumulation of H-2 in agglomerating vacancies during annealing can explain the sudden mass density increase. At higher temperatures, stress is released with the onset of H effusion. The H effusion consists of a two-stage process involving small open volume deficiencies and nanosized voids, contrasting earlier interpretations. The reduced amount of hydrogenmigration and enhanced hydrogen passivation degree are suggested as key factors to the reduced light-induced degradation associated with increased R values.
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