For further improvement of conversion efficiency in a-Si solar cells, it is necessary to develop materials with high photosensitivity in the long-wavelength region. A new solid phase crystallization (SPC) method was developed to grow a Si crystal at temperatures as low as 600°C. Using this method, high-quality thin-film polycrystalline silicon (poly-Si) with a Hall mobility of 70 cm2/V·s was obtained. Quantum efficiency in the range of 800 nm ∼ 1000 nm was achieved up to 80% in an experimental solar cell using the n-type poly-Si with a grain size of about 1.5 µm. Therefore, it was found that our SPC method was suitable as a new technique to prepare high-quality solar cell materials.
We have achieved the highest total area conversion efficiency for an integrated type 10cm × 10cm a-Si solar cell at 10.2%. This value is the world record for a 10cm × 10cm a-Si solar cell. For further improvement of conversion efficiency in a-Si solar cells, it is necessary to develop materials with high-photosensitivity in the long wavelength region and materials with high conductivity. We have developed a Solid Phase Crystallization (SPC) method of growing a Si crystal at temperatures as low as 600°C. Using this method, thin-film polycrystalline silicon (poly-Si) with higP-photosensitivity in the long wavelength region and Hall mobility of 70cm2/V sec was obtained and quantum efficiency in the range of 800,∼ lO00nm was achieved up to 80% in the n-type poly-Si with grain size of about 2μm. We also succeeded in preparing a device-quality p-type microcrystalline silicon (μc-Si) using the SPC method at 620°C for 3 hours from the conventional plasma-CVD p-type amorphous silicon (a-5i) withoul using any post-doping process. Obtained properties of μd=2 × 103 (.cm) and a high optical transmittance in the 2.0 ∼ 3.0 eV range are better as a window material than the conventional p-type μc-Si:H. Therefore, it was concluded that the SPC method is better as a new technique to prepare high-quality solar cell materials.
A high-efficiency integrated-type a-Si solar cell submodule with a size of 10cm × 10cm has been fabricated and a total area efficiency of 9.6% is obtained by using a high-quality p-layer doped with B(CH3)3 We have developed an advanced direct photo-CVD method. High-quallt” a-SI films with low tail characteristic energy and low light-induced degradation is prepared by this method. We have also studied the role of Si-H2 bonds on the light-induced effect. The result implies that Si-H bonds stabilize the defect states, resulting in a large light-induced degradation.
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