衬底温度对碲化镉薄膜性质及太阳电池性能的影响

doi:10.15541/jim20150310

摘要/Abstract

摘要：

蒸汽输运法是制备高质量且大面积均匀的CdTe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CdTe多晶薄膜, 并研究了衬底温度对CdTe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CdTe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℃), CdTe薄膜的平均晶粒尺寸从2 μm增大到约6 μm, CdTe薄膜的载流子浓度也从1.93×10¹⁰cm^-3提高到2.36×10¹³ cm^-3, 说明提高衬底温度能够降低CdTe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CdTe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CdTe薄膜太阳电池的转换效率达到11.2%。

关键词: 蒸汽输运法, CdTe薄膜, 衬底温度, 转换效率

Abstract:

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 investigated. 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 deposition 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 1.93×10¹⁰ cm^-3to 2.36×10¹³cm^-3when 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 substrate temperatures demonstrates that high substrate temperature (610℃) can greatly improve the efficiency, open circuit voltage and fill factor of the solar cells. But the substrate temperature higher than 610℃ will reduce the spectral response 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%.

Key words: vapor transport deposition, CdTe thin film, substrate temperature, conversion efficiency

中图分类号:

TQ174

曹胜, 武莉莉, 冯良桓, 王文武, 张静全, 郁骁骑, 李鑫鑫, 李卫, 黎兵. 衬底温度对碲化镉薄膜性质及太阳电池性能的影响[J]. 无机材料学报, 2016, 31(2): 141-147.

CAO Sheng, WU Li-Li, FENG Liang-Huan, WANG Wen-Wu, ZHANG Jing-Quan, YU Xiao-Qi, LI Xin-Xin, LI Wei, LI Bing. Effect of Substrate Temperature on CdTe Thin Film Property and Solar Cell Performance[J]. Journal of Inorganic Materials, 2016, 31(2): 141-147.

图/表 10

图1 VTD装置示意图

Fig. 1 Schematic diagram of VTD system

图2 不同衬底温度下刚沉积CdTe薄膜的XRD图谱

Fig. 2 XRD patterns of CdTe films deposited at different substrate temperatures

表1 不同衬底温度下刚沉积CdTe薄膜的织构系数Ci及标准方差σ

Table 1 Texture coefficient Ci and standard deviation σ of CdTe films for different substrate temperatures

Substrate temperature/℃	C_i					σ
Substrate temperature/℃	(111)	(220)	(311)	(440)	(331)	σ
520	2.98	0.10	0.96	0.27	0.67	1.04
550	4.79	0.01	0.05	0.01	0.13	1.89
580	3.44	0.14	0.43	0.31	0.66	1.23
620	4.45	0.03	0.15	0.06	0.36	1.72
640	3.96	0.06	0.22	0.11	0.65	1.49

图3 不同衬底温度下刚沉积CdTe薄膜的SEM表面照片

Fig. 3 SEM images of CdTe films deposited at different substrate temperatures (a) 520℃; (b) 550℃; (c) 580℃; (d) 620℃; (e) 640℃

图4 不同衬底温度下刚沉积的CdTe薄膜的晶粒尺寸分布图

Fig. 4 Distribution of average grain size of CdTe films deposited at different substrate temperatures

图5 不同衬底温度下刚沉积CdTe薄膜的透过谱(a)和光能隙图(b)

Fig. 5 Optical transmittance spectra (a) and band-gap of CdTe films (b) deposited at different substrate temperatures

表2 不同衬底温度条件下刚沉积CdTe薄膜的电学性质参数

Table 2 Electrical parameters of CdTe films deposited at different substrate temperatures

Substrate temperature	Electrical parameters (300 K)			Activation energy
Substrate temperature	ρ/ (Ω·cm)	R_sh/ (Ω·□^-1)	P /cm^-3	μ/ (cm²·V^-1·s^-1)	E_a/eV	E_ap/eV	E_aμ/eV
520℃	1.76×10⁶	3.84×10⁹	1.93×10¹⁰	-	0.576	0.608	-
580℃	2.94×10⁶	6.75×10⁹	1.96×10¹²	1.171	0.554	0.369	0.178
620℃	5.84×10⁵	1.34×10⁹	2.36×10¹³	0.756	0.509	0.277	0.192

图6 不同衬底温度条件下刚沉积CdTe薄膜的电子学性质与温度的关系

Fig. 6 Temperature-dependency of electronic properties of CdTe films deposited at different substrate temperatures

图7 不同衬底温度下制备的CdTe薄膜电池性能的各项参数

Fig. 7 Performance parameters of CdTe cells as a function of substrate temperature

图8 不同衬底温度下制备的CdTe薄膜电池的外量子效率曲线

Fig. 8 Measured EQE spectra of CdTe cells deposited at different substrate temperatures

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