Performance Improvement of Hydrogenated Nanocrystalline Silicon Solar Cells by Hydrogen Dilution Profiling

We have carried out a systematic study on metastability of n-i-p nc-Si:H solar cells with various hydrogen dilution profiles and correlate the results with the material structural properties. We find that the nc-Si:H single-junction cells with a hydrogen dilution profile show not only improved initial efficiency, but also better stability than those with a constant hydrogen dilution. Raman measurements using different excitation wavelengths show that the cells with the improved stability due to the hydrogen dilution profiling have a significant amorphous component, especially near the i/p interface. We speculate that the amorphous volume fraction in the material is not the key parameter for determining the stability of nc-Si:H cells. Other factors, such as the distribution and structure of the amorphous phase and the grain boundary regions, can affect the overall cell stability. By carefully optimizing the hydrogen dilution profiling, we have achieved initial and stable efficiencies of 9.0% and 8.5% in a nc-Si:H single junction, and 14.1% and 13.3% in an a-Si:H/nc-Si:H/nc-Si:H triple-junction structure, respectively