衬底温度对碲化镉薄膜性质及太阳电池性能的影响

Effect of Substrate Temperature on Cd Te Thin Film Property and Solar Cell Performance

蒸汽输运法是制备高质量且大面积均匀的Cd Te薄膜的一种优良的方法。采用自主研发的一套蒸汽输运沉积系统制备了Cd Te多晶薄膜,并研究了衬底温度对Cd Te薄膜性质及太阳电池性能的影响。利用XRD、SEM、UV-Vis和Hall等测试手段研究了衬底温度对薄膜的结构、光学性质和电学性质的影响。结果表明,蒸汽输运法制备的Cd Te薄膜具有立方相结构,且沿（111）方向高度择优。随着衬底温度的升高（520℃~640℃）,Cd Te薄膜的平均晶粒尺寸从2μm增大到约6μm,Cd Te薄膜的载流子浓度也从1.93×10^10 cm–3提高到2.36×10^13 cm–3,说明提高衬底温度能够降低Cd Te薄膜的缺陷复合,使薄膜的p型更强。实验进一步研究了衬底温度对Cd Te薄膜太阳电池性能的影响,结果表明适当提高衬底温度,能够大幅度提高电池的效率、开路电压和填充因子,但是过高的衬底温度又会降低电池的长波光谱响应,导致电池转换效率的下降。经过参数优化,在衬底温度为610℃、无背接触层小面积Cd Te薄膜太阳电池的转换效率达到11.2%。

Vapor transport deposition is an excellent method for preparing large area CdTe thin films with high quality and uniformity. Polycrystalline CdTe thin films were deposited by home-made vapor transport deposition system （VTD）. The effects of substrate temperature on the property of CdTe film and the performance of CdTe solar cell were inves- tigated. CdTe thin films were characterized by scanning electron microscope （SEM）, X-ray diffraction （XRD）, UV-Vis spectrometer, and Hall Effect system. The results show that the CdTe thin films deposited by vapor transport deposi- tion are cubic phase with a preferred orientation in （111） direction. The average grain size increases from 2 μm to 6 μm and the carrier concentration increases from 1.93 × 10^10 cm3 to 2.36×10^13 cm-3 when the substrate temperature increases from 520 ℃ to 620℃. This suggests that high substrate temperature can increase the carrier density significantly due to the suppressed defect recombination. The performance of CdTe thin film solar cells deposited at different sub- strate temperatures demonstrates that high substrate temperature （610℃） can greatly improve the efficiency, open cir- cuit voltage and fill factor of the solar cells. But the substrate temperature higher than 610℃ will reduce the spectralresponse of the cells in long wavelength region, which results in the degradation of solar cell performance. The small-area CdTe thin film solar cell without back contact layer deposited at substrate temperature of 610℃ obtains the best conversion efficiency of 11.2%.