Production Technology of High-Efficiency Amorphous Solar Cells by Radical Control

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The purpose of this study is to develop a new process technology to prepare high-quality amorphous thin films for high-efficiency solar cells. We have introduced hydrogen-radical CVD in which hydrogen radicals may affect both gas phase reaction and surface reaction and tried to prepare silicon related films such as a-Si : H,mu c-Si : H,a-SiC : H and mu c-SiC : H.Moreover, analysis of deposition mechanism and measurements of hydrogen radical density was carried out.(1) It was found that, by changing the concentration of SiH4 or Si2H6, the effect of hydrogen radicals on growth surface can be controlled and mu c-Si : H as well as a-Si : H can be prepared. Low hydrogen content a-Si : H films with high photosensitivity and high stability under light illumination were obtained. Electrical characteristics in p-type and n-type films also was good.(2) a-SiC : H films were prepared by using source gases of Si2H6 and C2H2. It was found that by introducing C2H2 with microwave excitation film properties can be controlled in a wide range and films with high stability can be formed. By decreasing the concentration of Si2H6, mu c-Si : H films were produced.(3) Deposition mechanism in hydrogen-radical CVD was analyzed by computer simulation with a simplified one-dimensional model. As a result, it was estimated that radical species contributing to film deposition is effectively varied by changing source gas concentration.(4) Hydrogen radical density was evaluated by detecting a temperature change in a platinum wire with which hydrogen radicals collide from measurements of electric resistance, and its dependences on generation conditions and its distribution in a CVD chamber was clarified.