Preparation of highly crystalline germanous selenide photoelectronic thin films byclose-space sublimation process and its application in solar cells
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摘要: 硒化亚锗(GeSe)由于具有原材料储量丰富、绿色无毒、制备工艺简单和性质稳定等优势，近几年得到了广泛关注。采用近空间升华法制备了GeSe薄膜，对GeSe薄膜的结晶行为进行分析，并将其应用到器件结构为FTO/CdS/GeSe/聚(3-己基噻吩)(P3 HT)/C的太阳能电池中进行优化。首先，在蒸发步骤完成后引入退火工艺，能够有效促进GeSe薄膜晶化，使GeSe太阳能电池的光电转换效率(PCE)提高至0.743%。随后，通过衬底温度调节GeSe薄膜的晶化特性，发现衬底温度的提高有利于GeSe薄膜的晶化，但当衬底温度在300℃以上时，过高的温度会使GeSe从衬底上脱附，导致晶化程度下降，器件性能快速退化。在最佳的280℃衬底温度下，GeSe薄膜具有最大的晶粒尺寸和最强的光吸收、最高的电子寿命(τ)和电导率(σ)，获得了2.130%的PCE，其中开路电压(VOC)为0.299 Ｖ，短路电流密度(JSC)为16.815 mA·cm−2，填充因子(FF)为42.137%。以上研究为高晶化GeSe太阳能电池的制备和优化提供了可行的技术路线。Abstract: Germanous selenide (GeSe) has attracted extensive attention in recent years because of its abundant raw material reserves, green, non-toxic, simple preparation process and stable properties. GeSe thin films were prepared by close-space sublimation method. The crystallization behavior of GeSe thin films was analyzed and optimized for solar cells with FTO/CdS/GeSe/poly(3-hexylthiophene) (P3 HT)/C device structure. Firstly, the annealing process is introduced after the evaporation step, which can effectively promote the crystallization of GeSe thin film, so that the photoelectric conversion efficiency (PCE) of GeSe solar cells can be increased to 0.743%. Subsequently, by adjusting the crystallization characteristics of the GeSe film by the substrate temperature, it is found that the increase of the substrate temperature is conducive to the crystallization of the GeSe film, but when the substrate temperature is more than 300℃, the excessive temperature will make the GeSe desurbed from the substrate, resulting in a decrease in the degree of crystallization and rapid degradation of the device performance. At the optimum substrate temperature of 280℃, GeSe films have the largest grain size and the strongest light absorption, the highest electron lifetime (τ) and the highest electrical conductivity (σ), and the PCE of 2.130%, where the open circuit voltage (VOC) is 0.299V, and the short circuit current density (JSC) is 16.815 mA·cm−2. The filling factor (FF) is 42.137%. The above research provides a feasible technical route for the preparation and optimization of high crystalline GeSe solar cells.
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Key words:
- GeSe /
- solar cells /
- crystallization /
- substrate temperature /
- annealing
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图 1 GeSe太阳能电池结构图
P3 HT—Poly(3-hexylthiophene)
Figure 1. Structure diagram of GeSe solar cell
图 2 近空间升华法制备GeSe薄膜示意图
Figure 2. Preparation of GeSe thin films by close-space sublimation method
图 3 (a)未退火与退火GeSe薄膜的XRD图谱；未退火GeSe薄膜(b)和退火GeSe薄膜(c)的SEM图像
Figure 3. (a) XRD patterns of unannealed and annealed GeSe films; SEM images of unannealed GeSe film (b) and annealed GeSe film (c)
图 4 未退火与退火GeSe太阳能电池电流密度-电压(J-V)曲线
VOC—Open circuit voltage; JSC—Short circuit current density; FF—Filling factor; PCE—Photoelectric conversion efficiency
Figure 4. Current density-voltage (J-V) curves of unannealed and annealed GeSe solar cells
图 5 GeSe薄膜的拉曼图谱(a)和XPS图谱((b), (c))
Figure 5. Raman spectra (a) and XPS spectra ((b), (c)) of GeSe thin films
图 6 不同衬底温度下GeSe薄膜的XRD图谱(a)和SEM图像((b)~(f))
Figure 6. XRD patterns (a) and SEM images ((b)-(f)) of GeSe films under different substrate temperatures
图 7 不同衬底温度下GeSe薄膜太阳能电池的光态J-V曲线(a)、暗态J-V曲线(b)、外部量子效率(EQE)曲线(c)和EIS曲线(d)
Rs—Series resistance; Rrec—Composite resistance; Rco—Contact resistance; Z'—The real part of the impedance; Z'' —The imaginary part of the impedance; CPE—Constant phase element
Figure 7. Light J-V curves (a), dark state J-V curves (b), external quantum efficiency (EQE) curves (c) and EIS impedance fitting curves (d) of GeSe thin film solar cells under different substrate temperatures
图 8 不同衬底温度下GeSe吸光层的电流-电压(I-V)曲线
Figure 8. Current-voltage (I-V) curves of GeSe absorbent layer at different substrate temperatures
图 9 不同衬底温度下GeSe吸光层紫外-可见吸收光谱图(插图为对应GeSe薄膜的光学带隙图）
α—Absorption coefficient; hv—Photon energy
Figure 9. Ultraviolet-visible absorption spectra of the GeSe absorbent layer at different substrate temperatures (The illustration is the optical band gap diagram of the corresponding GeSe film)
表 1 不同衬底温度下GeSe薄膜太阳能电池的性能参数
Table 1. Performance parameters of GeSe thin film solar cells under different substrate temperatures
Substrate temperature/℃ VOC/V JSC/(mA·cm−2) FF/% PCE/% Grain size/nm τ/μs J0/(mA·cm−2) 220 0.228 0.211 22.571 0.011 18.855 34 3.123×10−5 240 0.242 7.747 33.749 0.632 23.353 67 9.912×10−7 260 0.269 10.892 40.137 1.178 48.079 89 8.091×10−7 280 0.299 16.815 42.137 2.130 54.490 108 6.891×10−8 300 0.225 5.583 31.906 0.401 40.867 42 1.328×10−6 Notes: τ—Specific conductance; J0—Reverse saturation current density. 
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表 2 EIS阻抗图中拟合阻抗参数
Table 2. Impedance parameters fitted in the EIS impedance diagram
Substrate temperature/℃ Rs/Ω Rrec/Ω Rco/Ω 220 147 6290 178 240 141 11500 167 260 135 14600 127 280 108 17420 60 300 140 6470 77
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表 3 不同制备方法GeSe薄膜太阳能电池的特征参数
Table 3. Characteristic parameters of GeSe thin film solar cells prepared by different methods
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