Improvement of hydrogenated microcrystalline silicon solar cell performance by VHF power profiling technique

Hydrogenated microcrystalline silicon (μc-Si:H) solar cells were deposited with very high frequency plasma-enhanced chemical vapor deposition (VHF-PECVD) process at high deposition rates in high-power and a high-pressure regime. A novel VHF power profiling technique, designed by dynamically decreasing the VHF power step by step during the deposition of μc-Si:H intrinsic layers, has been developed for the first time to control the structural evolution along the growth direction. The profiling parameters such as the amount and the rate of change in VHF power were optimized in detail and the experimental results demonstrate that this technique not only controls the microstructure evolution but also results in reduced ion bombardments on growth surface. Using this method, a significant improvement in the solar cell performance has been achieved. A high conversion efficiency of 9.36% (Voc=542 mV, Jsc=25.4 mA/cm2, FF=68%) was obtained for a single-junction μc-Si:H p–i–n solar cell at a deposition rate of 12 Å/s. Then, the single-junction solar cell was used as a bottom component in micromorph solar cell, which leads to an efficiency of 11.14% (Voc=1.367 V, Jsc=11.92 mA/cm2, FF=69.4%).