Optimization of high rate growth high quality μc-Si:H thin films and its application to the solar cells

A series of high rate growth mu c-Si:H thin films with different thicknesses were deposited by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) process with high power and high pressure. The microstructure of the mu c-Si: H thin films was studied by the Raman and XRD spectra. It was found that the crystal fraction and grain size increased with the thickness of the thin film when the thickness was less than 1000 nm, and then came to saturation when the thickness was higher than 1000 nm. However, the performance of solar cells decreased obviously, when the thickness increased from 1000 nm to 2000 nm. Considering the microstructure properties and the ion bombardment during the high rate process, we investigated the controlled microstructure evolution and the improved material quality by discharge power profiling, which improved the performance of solar cells. By optimizing the profiling parameters, such as the amount and the rate of change in discharge power, a high efficiency of 9.36% was obtained with an i-layer deposition rate of 1.2 nm/s. Furthermore, we used the improved mu c-Si:H cell in an a-Si:H/mu c-Si:H double-junction structure and achieved an initial active-area cell efficiency of 11.14%.