Study on laser pyrolysis to control silicon nanocrystal formation for novel photovolataic applications

Silicon (Si) has received great interest due to its wide variety of advantages such as material abundance, non-toxicity, and strong infra of technologies in semiconductor industries. On the other hand, the cost of silicon wafer has driven many researchers to develop the silicon-based thin film solar cells to reduce the silicon consumption in the industry process. In this sense, the silicon-based thin film solar cells including hydrogenated amorphous and microcrystalline silicon (a-Si:H, μc-Si:H) have good advantage in cost saving. However, a-Si:H solar cells have weaknesses in low efficiency (~9 %), light induced degradation, too high bandgap separation (1.7-1.8 eV) compared to its competing materials (i.e., crystalline silicon, CdTe, and CIGS) for photovoltaic applications. To cope with these relative weaknesses of current silicon-based thin film technology, we propose a hybrid-type light absorbing materials with single crystal silicon nano-particles (Si-NPs) prepared by laser pyrolysis within a-Si:H thin film matrix. For this hybrid-type solar cell application, single crystal Si-NPs were synthesized by SiH₄ gas decomposition using CO₂ laser pyrolysis. Many process parameters of laser pyrolysis were calibrated to form Si-NPs with various characteristics. The crystalline properties and sizes of Si-NPs were varied by changing CO₂ laser power, reactive gas pressure, and H₂/SiH₄ gas flows. Transmission Electron Microscopy (TEM) analyses were employed to verify their sizes and crystallinities according to the process parameters. We found that the laser pyrolysis are controllable to synthesize single crystal Si-NPs with diameters of 5-15 nm and the synthesized Si-NPs are applicable to solar cell fabrication.