Si衬底Cu_(2)ZnSnS_(4)太阳能电池的数值分析

Numerical analysis of Cu_(2)ZnSnS_(4) solar cells on Si substrate

在Si衬底上制备的Cu_(2)ZnSnS_(4)(CZTS)太阳能电池具有CZTS与Si衬底的晶格失配低的优点,但目前其转换效率仍较低.本文采用异质结太阳能电池仿真软件Afors-het对Si衬底CZTS太阳能电池进行数值计算.对现有的p-CZTS/n-Si太阳能电池的计算结果表明,在该电池结构中p-CZTS和n-Si分别起窗口层和吸收层的作用,但p-CZTS具有高光吸收系数,使大部分入射光无法透过p-CZTS层进而被n-Si吸收,限制了电池的转换效率.本文提出以p-Si作为衬底的n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si太阳能电池结构.计算得到的p-CZTS/p-Si结构的暗态电流密度-电压(J–V)特性曲线均为线性曲线,表明p-CZTS与p-Si为欧姆接触以及p-Si作为p-CZTS的背电极的可行性.进一步计算了p-Si的厚度与掺杂浓度、p-CZTS的厚度与掺杂浓度对n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si太阳能电池光伏特性的影响,在不考虑寄生串并联电阻效应和缺陷态的理想情况下,电池的最高转换效率为28.41%.本文计算结果表明,n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si太阳能电池可解决现有p-CZTS/n-Si结构存在的问题,是一种合适的Si衬底CZTS太阳能电池结构.

The Cu_(2)ZnSnS_(4)(CZTS)solar cell prepared on Si substrate has an advantage of low lattice mismatch between CZTS and Si substrate,but the conversion efficiency of reported p-CZTS/n-Si solar cells is still low at present.In this work,the CZTS solar cells on Si substrate are calculated numerically by heterojunction solar cell simulation software Afors-het.The calculated results show that the p-CZTS and n-Si act as window layer and absorber respectively in the p-CZTS/n-Si solar cell because the band gap of p-CZTS is larger than that of n-Si.The conversion efficiency of p-CZTS/n-Si solar cell increases as the thickness of p-CZTS window layer decreases.The highest calculated conversion efficiency of p-CZTS/n-Si solar cell is 18.57%.In the best p-CZTS/n-Si solar cell,most of the incident light cannot pass through the p-CZTS window layer due to the high absorption coefficient of p-CZTS,which limits the conversion efficiency of solar cell.In order to solve the problems existing in the p-CZTS/n-Si structure,a novel n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si solar cell structure is proposed,where n-ZnO:Al and i-ZnO are window layers,n-CdS is buffer layer,p-CZTS is absorber,and p-Si is substrate and back electrode.The dark current density-voltage(J-V)characteristic curves of p-CZTS/p-Si structure varying with the thickness and doping concentration of p-Si and the doping concentration of p-CZTS are calculated to investigate the feasibility of p-Si as a back electrode of p-CZTS.All the calculated J-V characteristic curves of p-CZTS/p-Si structure are linear,indicating the formation of ohmic contact between p-CZTS and p-Si.The photovoltaic properties of n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si solar cell are further calculated.The built-in electric field distributed in n-ZnO:Al,i-ZnO,n-CdS,and p-CZTS contribute to the collection of photo-generated carriers.The conversion efficiency of n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si solar cell is enhanced with the decrease of the thickness of p-Si and the increase of doping concentrations of p-Si and p-CZTS and the thickness of p-CZTS.Without considering the effect of parasitic series resistance and parallel resistance and defect states,the highest conversion efficiency of ideal n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si solar cell is 28.41%.The calculated results in this work show that the n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si solar cell has an appropriate structure for CZTS solar cell on Si substrate.