摘要
热光伏发电技术具有高效率、高功率密度、适应热源广泛等特征,揭示其核心部件—电池芯片内部光电能量转换物理机制及影响规律,有利于系统性能的进一步提升。针对GaSb热光伏电池内部的光-电转换过程,建立了微观载流子输运模型,采用光-电耦合仿真方法对其性能参数进行了数值模拟。重点探究了入射辐射光谱特性及功率密度对电池性能的影响。结果表明:当入射光谱辐射功率相同时,电池转换效率随光谱变化呈现明显的非单调性,在波长1.42 μm处达到峰值22.50%。同一光谱下,随着辐射功率密度提高,电池最大输出电功率密度等比例增大,转换效率也随之增大但增幅逐渐减小,波长1.42 μm时增幅最大约4.85%。
“双碳”战略要求构建清洁低碳、安全高效的能源体
通过对光伏电池内部的光电转换机理探索及分析,能够有效指导电池的设计、制备及测量评
除了电池材
本文针对不同功率下辐射源的连续光谱特性进行了详细的数值模拟与分析,以期更精确地指导辐射源的优化。基于光-电耦合数值仿真方法,重点探究了辐射源的光谱分布特性及功率密度对GaSb热光伏电池性能的影响。建立GaSb电池的载流子输运物理模型,通过计算对比验证了模拟方法的可靠性,进一步分析电池性能参数以及内部载流子特性参数。通过对电能输出特性分析,获得辐射源的光谱特性和功率密度对GaSb电池性能参数的影响规律。
如

图1 GaSb热光伏电池模型示意图
Fig. 1 Schematic of GaSb thermophotovoltaic cell model
热光伏电池内部辐射能-电能转换过程的控制方程包括载流子输运方程和泊松方程。其中,载流子输运方
, | (1) |
式中,n、p分别为电子、空穴的浓度,μ为载流子迁移率(下角标中n和p分别代表电子和空穴),Nn、Np分别为施主、受主掺杂浓度,NC、NV分别为有效导带、价带态密度,q为电荷量,ϕ为静电势,kB为玻尔兹曼常数,D、DT分别为扩散系数、热扩散系数,T为载流子和晶格的温度。结合泊松方程即
, | (2) |
式中,ρ为空间电荷密度,ε0为真空介电常数,εr为相对介电常数。
载流子浓度的变化主要由其产生与复合两个过程决定。其中,载流子的生成过程主要指光伏电池在束缚的电子(空穴)内受到光子激发后完成能带跃迁产生自由电子(空穴)的过程。载流子生成率定义为单位时间单位体积内被吸收光子转化为载流子的数
, | (3) |
式中,G为全光谱辐射下载流子生成率,g(λ, x)为某特定波长辐射下载流子生成率,λbg为半导体材料的截止波长,α(λ)为光谱吸收系数,R(λ)为光谱反射率,q(λ)为特定波长的入射辐射功率,x为电池内沿光传播方向某一点离光入射表面的距离,h为普朗克常数,c为真空中的光速。
载流子的复合过程主要指被激发的自由电子(空穴)重新形成电子空穴对并且释放能量的过程,可以分为体复合和表面复合两类。其中,体复合又包括直接复合、缺陷复合和俄歇复
, | (4) |
式中,Urad、USRH和UAug分别为载流子直接复合率、缺陷复合率和俄歇复合率,rrad、rAug和τSRH分别为载流子的直接复合因子、俄歇复合因子和缺陷复合因子。
表面复合存在于半导体材料表面或不同半导体材料及多晶体材料的界面,可由
, | (5) |
式中,W为载流子表面复合率,S为载流子的表面复合因子,n0、p0分别为导带、价带中自由电子、空穴的粒子数密度。
此外,电池效率由
, | (6) |
式中,Pe,max为电池最大输出电功率,Pin为入射辐射功率,针对黑体辐射器,其辐射功率由
, | (7) |
式中,c1 = 3.74×1
基于上述理论模型,对热光伏电池的能量转换过程进行数值模拟。高温辐射源设置在热光伏电池上面,电池上表面为金属正电极,采用半导体-金属的理想欧姆接触,下表面为负电极,为半导体-金属接触的理想欧姆接触,假设电池整体的温度均匀恒定(Tc = 300 K)。
为验证本文光-电耦合计算方法的可靠性,采用与文献[

(a)

(b)
图2 本文(a) J-V曲线与(b) P-V曲线计算结果与文献[
Fig. 2 Comparison of the (a) J-V curves and (b) P-V curves in this work with that in Ref. [
Result | Pe, max / (W·c | JSC / (A·c | VOC / (V) | FF |
---|---|---|---|---|
Ref. [ | 0.527 | 1.484 | 0.457 | 0.777 |
This work | 0.528 | 1.484 | 0.456 | 0.781 |
Parameter | Value | Reference |
---|---|---|
μn / (c | 4 484.83 |
[ |
μp / (c | 378.51 |
[ |
rrad / (c |
8.5×1 |
[ |
τn,SRH / ns | 11 |
[ |
τp,SRH / ns | 600 |
[ |
rn(p),Aug / (c |
3×1 |
[ |
Sn(p)/ (cm· |
1×1 |
[ |
针对典型GaSb热光伏电池内部的能量转换过程进行分析,电池模型的厚

(a)

(b)
图3 (a) 2000 K黑体光谱辐射力,(b) GaSb材料的复折射
Fig. 3 Diagrams of (a) the blackbody radiation intensity at 2000 K and (b) the complex refractive index of GaS
GaSb热光伏电池的J-V及P-V特性曲线如

图4 2000 K黑体辐射下GaSb热光伏电池的J-V及P-V特性曲线
Fig. 4 Diagram of J-V and P-V curves for the GaSb thermophotovoltaic cell under 2000 K blackbody radiation
在V0=0.47 V时,电池内部准费米能级差值(EFn-EFp)和静电势(Φ)在厚度方向的变化如

(a)

(b)
图5 电池内部的 (a) 准费米能级差值及 (b) 静电势
Fig. 5 Diagrams of (a) the Quasi Fermi level difference and (b) the electrostatic potential in the cell
当电压V0=0.47 V时,电池内部非平衡载流子的分布情况如

(a)

(b)
图6 电池内部的 (a) 载流子浓度及 (b) 载流子生成/复合率
Fig. 6 Diagrams of (a) the carrier concentration and (b) the carrier generation/recombination rate in the cell
本节针对不同辐射光谱下GaSb热光伏电池的电输出性能进行了研究。各个波长的入射光谱辐射功率密度(Pin, λ)均为0.1 W/c
开路电压、最大输出电功率密度对应电压、填充因子和电池效率随入射辐射光谱的变化如

(a)

(b)

(c)

(d)
图7 不同辐射光谱下电池的性能参数: (a) J-V特性曲线,(b) 短路电流密度,(c) P-V特性曲线,(d) 最大输出电功率密度
Fig.7 Diagrams of performance characteristics of the cell under different wavelength: (a) J-V characteristic curves, (b) short-circuit current density, (c) P-V characteristic curves, (d) maximum output electric power intensity

(a)

(b)
图8 不同辐射光谱下电池的 (a) 开路电压及最大输出电功率密度对应电压, (b) 填充因子和电池效率
Fig.8 Diagrams of (a) open circuit voltage and corresponding voltage of maximum output electric power intensity, (b) filling factor and efficiency of the cell under different wavelengths
效率与短路电流密度的变化趋势一致,在0.5~1.42 μm波段内增加了20.45%,在波长1.42 μm时达到峰值。基于上述结果可知,通过优化辐射源的光谱分布,即减小低效率波长的辐射功率的同时增大高效率波长的辐射功率,更好地匹配热光伏电池能量转换效率的光谱曲线,从而提升TPV系统的热-电转换性能。
本节讨论入射光谱辐射功率密度(Pin, λ)变化时(从0.1 W/c

(a)

(b)
图9 不同辐射功率密度下电池的 (a) J-V及 (b) P-V特性曲线
Fig. 9 Diagrams of (a) J-V and (b) P-V characteristic curves of the cell under different incident power intensities
如

(a)

(b)
图10 不同辐射功率密度下电池的 (a) 开路电压及最大输出功率密度对应电压, (b) 填充因子和电池效率
Fig. 10 Diagrams of (a) open circuit voltage and corresponding voltage of maximum output electric power intensity, (b) filling factor and efficiency of the cell under different incident power intensities
在0.5~1.8 μm波段内各个入射波长下,电池效率的光谱曲线随入射光谱辐射功率密度(Pin, λ)的变化如

图11 不同入射光谱辐射功率密度下GaSb电池转换效率的光谱曲线
Fig. 11 Diagram of the spectral curves for the cell efficiency under different incident power intensities
本文采用光-电耦合方法数值模拟了GaSb热光伏电池的热辐射能-电能转换过程,计算了电池内部的载流子分布与输运情况,针对微观载流子输运特性以及宏观电性能表征进行了详细分析;研究了辐射源的光谱特性及功率密度对电池性能的具体影响。主要结论如下:
(1) 入射光谱辐射功率密度一定,随入射波长的增加,GaSb热光伏电池各性能参数均产生明显的非单调性变化趋势。光谱功率密度0.1 W/c
(2) 入射辐射光谱一定时,随辐射功率的增加,GaSb电池最大输出电功率整体呈线性上升趋势,转换效率有所增大但增幅逐渐减小。λ=1.42 μm时,入射光谱辐射功率密度从0.1 W/c
(3) 在不同入射波长下,随着辐射功率密度的增加,电池的转换效率整体提高。入射光谱辐射功率密度由0.1 W/c
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