Combining strong interface recombination with bandgap narrowing and short diffusion length in Cu2ZnSnS4 device modeling
Combining strong interface recombination with bandgap narrowing and short diffusion length in Cu2ZnSnS4 device modeling
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DOI：
10.1016/j.solmat.2015.09.019
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发表时间：
2016
影响因子：
6.9
通讯作者：
C. Frisk;T. Ericson;Shuyi Li;P. Szaniawski;J. Olsson;C. Platzer‐Björkman
中科院分区：
文献类型：
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作者：
C. Frisk;T. Ericson;Shuyi Li;P. Szaniawski;J. Olsson;C. Platzer‐Björkman
在本工作中，我们建立了一个集成带隙缩小、短少数载流子扩散长度和界面重组的SCAPS器件模型。该模型基于标准结构的参考装置；在碱石灰玻璃上溅射Mo，反应溅射退火cu2 znsns4 （CZTS）吸收层，化学浴沉积cd和溅射i-ZnO缓冲层，与溅射ZnO: Al和蒸发Ni/Al/Ni栅格形成正面接触。参考装置的效率为6.7%。吸收层的模型参数值是基于对参考器件上进行的温度相关的电流-电压（J-V - t）测量、电容-电压（C-V）和驱动级电容剖面（DLCP）测量的分析，以及模拟和测量的量子效率（QE）和电流-电压（J-V）性能的比较。其他参数取自文献。吸收层中电子-空穴对的产生和复合是本文研究的重点。当比较反射-透射（R-T）测量数据与椭偏测量和计算数据时，报告的CZTS吸收系数值相差约一个数量级。因此，从R-T和QE测量中提取的改进的半经验吸收系数，以及CV和DLCP的耗尽宽度，被提出并用于本研究。利用J-V-T分析评估了主要的复合路径，并从温度相关的开路电压（V OC）和修正的Arrhenius图中提取了零开尔文活化能（ea, 0）。在每种情况下，即使考虑到无序导致的带隙缩小，也发现ea， 0明显小于带隙能量，这表明在我们的CZTS器件中观察到的V OC赤字以界面复合为主。最后，建立了一个完整的器件模型，其中J-V和QE模拟与相应的测量结果吻合良好，其中界面对V OC亏损的影响最大，但块体复合的贡献明显，少数载流子扩散长度为250 nm，带隙缩小，其带隙能量低于标称带隙能量1.35 eV。
In this work we establish a device model in SCAPS, incorporating bandgap narrowing, short minority carrier diffusion length and interface recombination. The model is based on a reference device with standard structure; sputtered Mo on soda lime glass, a reactively sputtered and annealed Cu 2 ZnSnS 4 (CZTS) absorber layer, chemical bath deposited CdS and sputtered i-ZnO buffer layers, and front contact formed with sputtered ZnO: Al and an evaporated Ni/Al/Ni grid. The efficiency of the reference device is 6.7%. Model parameter values of the absorber layer are based on the analysis of temperature dependent current–voltage (J–V–T) measurements, capacitance–voltage (C–V) and drive-level capacitance profiling (DLCP) measurements, performed on the reference device, and on the comparison of simulated and measured quantum efficiency (QE) and current–voltage (J–V) performance. Additional parameters are taken from literature. The key elements, electron–hole pair generation and recombination in the absorber layer, are the main focus in this study. Reported values of the absorption coefficient of CZTS vary around one order of magnitude when comparing data from reflectance–transmission (R–T) measurements with ellipsometry measurements, and calculations. Therefore, a modified semi-empirical absorption coefficient, extracted from R–T and QE measurements, with the depletion width from CV and DLCP, is presented and used in this study. The dominating recombination path is evaluated with J–V–T analysis and the zero Kelvin activation energy (E A, 0) is extracted from both temperature dependent open circuit voltage (V OC) and from modified Arrhenius plots. In each case, E A, 0 is found to be substantially smaller than the bandgap energy, even when considering bandgap narrowing due to disorder, which is an indication that the V OC deficit observed in our CZTS device dominated by interface recombination. Finally, a complete device model is established, with J–V and QE simulations in good agreement with corresponding measurements, where the interface has the biggest impact on the V OC deficit, but with clear contribution from bulk recombination, with minority carrier diffusion length 250 nm, and from bandgap narrowing, giving a lower than nominal bandgap energy of 1.35 eV.