Effects of Hydrogen Concentration and Cooling Speed on Fabrication of Hydrogenated Amorphous Silicon: Quantum Simulation

In order to investigate various properties of hydrogenated amorphous silicon (a-Si:H) for improvement of low conversion efficiency and stability of solar cells, a series of quantum simulations based on the density functional theory combined with the tight binding model were performed for a-Si:H with various hydrogen concentrations and cooling rates. The radial distribution function (RDF) for Si-Si pairs indicates that samples with higher H concentration (20% and 25%) give a structure in better agreement with experiments, but the RDF of Si-H pairs suggests that samples with lower H concentration (14%) may give more appropriate structure. The coordination number (Nc) analysis indicates that more defects (dangling bonds and floating bonds) exist in 20% and 25% H concentration samples. Overall, a-Si:H with 14% H concentration gives most preferable structure. The cooling rate has also much effect on the structure. Sample with the slowest cooling rate is slightly more structured based on Si-Si pair RDF and Nc. The electron transport of a-Si and a-Si:H were evaluated and the superiority of a-Si:H was confirmed.