Correlation of hydrogenated nanocrystalline silicon microstructure and solar cell performance

We used Raman and photoluminescence (PL) spectroscopy to study the relationship between the material properties and the solar cell performance of hydrogenated nanocrystalline silicon (nc-Si:H). The crystalline volume fraction (f(c)) was deduced from the Raman spectrum. Generally, a high f(c) leads to a high short circuit current density and a low open circuit voltage. PL spectra were measured using 632.8-nm and 442-nm laser lines. There are two distinguished PL peaks at 80 K, one at similar to1.4 eV originating from the amorphous region, while the other at less than or equal to 0.9 eV from the nanocrystalline grain boundary regions. Generally, the intensity fraction of this low energy PL peak, I-PLc/(I-PLa+I-PLc), was larger for 442-nm than 632.8-nm excitation, indicating an increase in crystallinity along the growth direction. However, for the best initial performance cells obtained by H-2 dilution profiling and the i/p buffer layer, the intensity fraction I-PLc/(I-PLa+I-PLc) decreased from the bulk to the top i/p interface. The Raman and PL results give insight into the correlation between the microstructures and the cell performance, and verified that properly-controlled crystallinity in the intrinsic layer and buffer layer at the i/p interface layer are important for optimizing nc-Si:H solar cells.