We present our development of n-type nano-structured hydrogenated silicon oxide (nc-SiOx:H) as a dual-function layer in multi-junction solar cells. We optimized nc-SiOx:H and attained a conductivity suitable for a doped layer and optical property suitable for an inter-reflection layer. We tested the effectiveness of the dual-function nc-SiOx:H layer by replacing the normal n layer between the middle and the bottom cells in an a-Si:H/a-SiGe:H/nc-Si:H triple-junction structure. A significant gain in the middle cell current density of ∼1.0 mA/cm2 is achieved. We further optimized the component cells and the triple-junction structures and attained an initial active-area cell efficiency of 16.3%.

We have studied the effect of texture in Ag/ZnO back reflectors (BRs) on the performance of hydrogenated nanocrystalline silicon (nc-Si:H) solar cells. While a larger texture provides superior light trapping, it also deteriorates the nc-Si:H quality. We have used total and diffused reflection and atomic force microscopy to evaluate the BR texture. A BR with textured Ag and thin ZnO layers has been found to give the best cell performance. Using the optimized BR, we have achieved an initial active-area efficiency of 10.2% in a nc-Si:H single-junction cell and a stable total-area efficiency of 12.5% in a hydrogenated amorphous silicon/nc-Si:H/nc-Si:H triple-junction cell.

We show experimentally that the photocurrent of thin-film hydrogenated microcrystalline silicon (lc-Si:H) solar cells can be enhanced by 4.5 mA/cm 2 with a plasmonic back reflector (BR). The light trapping performance is improved using plasmonic BR with broader angular scattering and lower parasitic absorption loss through tuning the size of silver nanoparticles. The lc-Si:H solar cells deposited on the improved plasmonic BR demonstrate a high photocurrent of 26.3 mA/cm 2 which is comparable to the state-of-the-art textured Ag/ZnO BR. The commonly observed deterioration of fill factor is avoided by using lc-SiO x :H as the n-layer for solar cells deposited on plasmonic BR. V C 2013 AIP Publishing LLC [http://dx

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We report our recent progress on nc-Si:H single-junction and a-Si:H/nc-Si:H/nc-Si:H triple-junction cells made by a modified very-high-frequency (MVHF) technique at deposition rates of 10-15 Å/s. First, we studied the effect of substrate texture on the nc-Si:H single-junction solar cell performance. We found that nc-Si:H single-junction cells made on bare stainless steel (SS) have a good fill factor (FF) of ˜0.73, while it decreased to ˜0.65 when the cells were deposited on textured Ag/ZnO back reflectors. The open-circuit voltage (Voc) also decreased. We used dark current-voltage (J-V), Raman, and X-ray diffraction (XRD) measurements to characterize the material properties. The dark J-V measurement showed that the reverse saturated current was increased by a factor of ˜30 when a textured Ag/ZnO back reflector was used. Raman results revealed that the nc-Si:H intrinsic layers in the two solar cells have similar crystallinity. However, they showed a different crystallographic orientation as indicated in XRD patterns. The material grown on Ag/ZnO has more random orientation than that on SS. These experimental results suggested that the deterioration of FF in nc-Si:H solar cells on textured Ag/ZnO was caused by poor nc-Si:H quality. Based on this study, we have improved our Ag/ZnO back reflector and the quality of nc-Si:H component cells and achieved an initial and stable active-area efficiencies of 13.4% and 12.1%, respectively, in an a-Si:H/nc-Si:H/nc-Si:H triple-junction cell.

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