Zn1-xMgxO能带结构及作为窗口层的CdTe薄膜太阳电池的SCAPS仿真应用

doi:10.15541/jim20170349

摘要/Abstract

摘要：

采用第一性原理广义梯度近似+U(GGA+U)方法计算了纤锌矿结构Zn_1-_xMg_xO(ZMO)(0≤x≤0.25)合金的能带结构。计算表明: 随着Mg组分增加, ZMO化合物的导带底及费米能级均向真空能级方向移动, 带隙增宽。基于理论计算得到ZMO的能带结构参数, 使用SCAPS软件对ZMO作窗口层的CdTe薄膜太阳电池的性能进行了仿真模拟, 并将研究结果与CdS作窗口层的CdTe太阳电池的性能进行了比较。结果表明: Mg在ZMO中的含量0≤x≤0.125时, ZMO/CdTe太阳电池具有比CdS/CdTe太阳电池更高的开路电压和短路电流密度; ZMO的导带底高出CdTe导带底约0.13 eV时, CdTe薄膜太阳电池的转换效率最高, 达到18.29%。这些结果为高效率碲化镉薄膜太阳电池的结构设计和器件制备提供了理论指导。

关键词: Zn_1-_xMg_xO, 能带结构, 薄膜太阳电池, 转换效率

Abstract:

In this paper, the band structure of Zn_1-_xMg_xO(ZMO) alloy with different Mg compositions by using first-principles calculations with GGA+U method was studied. The calculation results show that position of conduction band offset and Fermi level of Zn_1-_xMg_xO move towards the vacuum level while the band gap becomes wider with the increasing Mg concentration. Based on theoretical calculation results of ZMO, ZMO/CdTe, CdS/CdTe solar cells were modeled using SCAPS software and its device performances were simulated and analyzed in detail. The results indicate that the conversion efficiency of CdTe solar cell with ZMO is higher than that of solar cell with CdS due to the high open circuit voltage and short circuit current density when x in Zn_1-_xMg_xO is in the range of 0-0.125. Efficiency of CdTe solar cells with ZMO reaches 18.29% because the recombination decreases obviously resulting from appropriate conduction band offset about 0.13 eV at ZMO/CdTe interface. These data provide a theoretical guidance for design and fabrication of high efficiency CdTe solar cells.

Key words: Zn_1-_xMg_xO, band structure, solar cell, conversion efficiency

中图分类号:

O447

何旭, 任胜强, 李春秀, 武莉莉, 张静全, 都政. Zn_1-_xMg_xO能带结构及作为窗口层的CdTe薄膜太阳电池的SCAPS仿真应用[J]. 无机材料学报, 2018, 33(6): 635-640.

HE Xu, REN Sheng-Qiang, LI Chun-Xiu, WU Li-Li, ZHANG Jing-Quan, DU Zheng. Zn_1-_xMg_xO: Band Structure and Simulation as Window Layer for CdTe Solar Cell by SCAPS Software[J]. Journal of Inorganic Materials, 2018, 33(6): 635-640.

图/表 11

图1 ZnO(2×2×2)超晶胞模型

Fig. 1 Crystal structure of pure wurtzite bulk material ZnO supercell

图2 SCAPS中CdTe电池结构图

Fig. 2 Device structure of CdTe solar cells for the device simulations

表1 CdTe电池材料的参数设置

Table 1 Simulation parameters for the model of CdTe solar cells

Layer properties	FTO	CdS	Zn_1-_xMg_xO					CdTe	ZnTe:Cu
Layer properties	FTO	CdS	x=0	x=0.0625	x=0.125	x=0.1875	x=0.25	CdTe	ZnTe:Cu
ε/ε₀	8.9	9.0	9.0	9.0	9.0	9.0	9.0	10.0	10.1
N_c/cm^-3	5.2×10¹⁸	2.2×10¹⁸	4.0×10¹⁸	10¹⁷	9.0×10¹⁶	10¹⁶	10¹⁵	9.2×10¹⁷	1.5×10¹⁸
N_v/cm^-3	10¹⁹	1.80×10¹⁹	9.00×10¹⁸	10¹⁸	9.00×10¹⁷	10¹⁷	10¹⁶	5.20×10¹⁸	1.16×10¹⁹
μ_n/(cm²˖V^-1˖s^-1)	100	340	50	50	50	50	50	400	400
μ_p/(cm²˖V^-1˖s^-1)	25	50	20	20	20	20	20	60	50
N_A/cm^-3	10²⁰	10¹⁷	5.0×10¹⁷	10¹⁶	9.0×10¹⁵	10¹⁵	9.0×10¹⁴	1.5×10¹⁴	1.5×10²⁰
Thickness/nm	3.5×10²	10²	10²	10²	10²	10²	10²	5.0×10³	70.0

图3 本征半导体ZnO能带结构

Fig. 3 Calculated band structure of pure ZnO

图4 不同Mg含量下的ZMO薄膜透过光谱图(a)和光学带隙图谱(b)

Fig. 4 Optical transmittance spectra (a) and band-gap (b) of ZMO films

图5 Zn1-xMgxO带隙值随x变化的关系曲线

Fig. 5 The bandgaps of wurtzite Zn1-xMgxO alloy as a function of Mg concentration x

表2 ZMO在不同x值下的带隙、费米能级、电子亲和势与功函数的值

Table 2 Bandgap, Fermi level, electron affinity and work function of ZMO with different x

x	ΔE_c/eV	E_g/eV	E_f/eV	χ/eV	φ/eV
0	-0.03	3.32	2.48	4.53	5.31
0.0625	0.06	3.41	2.53	4.44	5.18
0.125	0.13	3.48	2.86	4.37	4.99
0.1875	0.29	3.65	2.91	4.21	4.84
0.25	0.47	3.82	3.02	4.03	4.83

图6 ZMO/CdTe异质结能带结构

Fig. 6 Schematic energy band diagram of ZMO/CdTe Layers(a) x=0; (b) x=0.125; (d) x=0.25

表3 SCAPS 模拟CdS/CdTe和ZMO/CdTe电池的输出参数

Table 3 Performances of the CdS/CdTe and ZMO/CdTe solar cells with SCAPS

	CdS	Zn_1-_xMg_xO
	CdS	x=0	x=0.0625	x=0.125	x=0.1875	x=0.25
V_oc/mV	821	825	829	837	838	928
J_sc/(mA•cm^-2)	24.34	27.88	28.22	28.36	27.95	0.20
FF/%	75.32	75.08	76.77	77.02	53.05	8.27
η/%	15.06	17.28	17.98	18.29	12.42	0.01

图7 CdS/CdTe和ZMO/CdTe电池的J-V特性曲线

Fig. 7 J-V curves of CdTe solar cells with CdS and ZMO as window layers

图8 CdS/CdTe和Zn1-xMgxO/CdTe电池的量子效率

Fig. 8 Quantum efficiency of CdTe solar cells with CdS and Zn1-xMgxO as window layers

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