高效、环保Cu2ZnSn(S,Se)4薄膜太阳电池的设计和制备及相关物理问题

It is well known that the difficult in appliaction of Cu2ZnSn(S,Se)4(CZTSSe) thin film solar cell is low conversion efficiency, which results mainly from large series resistance,induced by high resistance of the CZTSSe film and non-ohm contact between tha CZTSSe and back electrode,and low open circuit voltage reduced by mismatch of the interface of buffer layer and CZTSSe.To solve the problems,it is suggested in the present project to synthesize CZTSSe target under high pressure,and then grow the CZTSSe films by using of sputtering or PLD and the target and finally anneal the films under high pressure non-toxic gas,the whole fabriaction process is non-toxic and composition controllable, and the electrical resistance of the film can be decreased by optimizing the composition,native deffects.grain size and density of the film via adjusting the pressure and temperature; to study structure and electrical properties of the CZTSSe/back electrode interface and effect of them on the series resistance, searching approach of preparation of the ohm contact interface with low resistance;to prepare CZTSSe based solar cell using (Cd1-xZnx)S or Zn(S,O)alloy as buffer layers, investigating effects of the buffer layers'properties as well as lattice mismatch and band alignment between the buffer layers and CZTSSe on structure and proeprties of the built-in fild, and segregation,recombination and transportation of photo-generated electron and hole, and exploring method and technique of improvement of open circuit voltage. We will decrease the series resistance and increase open circuit voltage by optimizing the structure of the solar cell as well as its praparation approach and technique, so that fabircate non-toxic CZTSSe based solar cell with high conversion efficiency.

目前Cu2ZnSn(S,Se)4(CZTSSe)薄膜太阳电池难以应用的关键是转换效率低，这主要是由于CZTSSe薄膜的高电阻及其与背电极的非欧姆接触导致的串联电阻大和CZTSSe与过渡层不匹配引起的开路电压小造成的。为此，本项目提出利用高压合成和后热处理新技术制备CZTSSe薄膜，通过调整压力和温度控制薄膜成分、减少本征缺陷、提高晶粒尺寸和致密度以降低薄膜电阻；研究CZTSSe与背电极界面的结构和电性及其对串联电阻的影响和机制，探索实现低阻欧姆接触的方法和技术；制备以（Cd1-xZnx）S或Zn(S,O)为过渡层的CZTSSe太阳电池，研究过渡层的性能及其与CZTSSe的晶格失配和能带排列方式对内建电场的结构和性能以及光生电子空穴的分离、复合和输运的影响规律和机制，探寻提高开路电压的方法和技术。通过优化电池结构和制备工艺，减少串联电阻，提高开路电压，制备高效、环保的CZTSSe太阳电池。

锌黄锡矿结构Cu2ZnSn(S,Se)4(CZTSSe)被认为是有望取代CuInGaSe2制备太阳电池的半导体材料。但目前CZTSSe太阳电池转换效率还很低，这主要是由CZTSSe晶体质量差、与背电极的非欧姆接触和与过渡层界面晶格和能带不匹配造成的。针对上述问题，本项目开展了高质量、单一相CZTSSe薄膜的制备，CZTSSe 本征缺陷调控，CZTSSe太阳电池内建电场和背电极的设计、表征、制备及其对转换效率影响的研究工作。取得如下重要结果：.利用高压和密封石英管高温硫化技术制备出晶粒尺寸达微米量级、致密的Cu2ZnSnS4(CZTS)块体和薄膜材料；.发展了一种通过提高以水-乙醇为溶剂的前驱体溶液稳定性生长大晶粒、高致密CZTSSe薄膜的新方法，制备出效率为7.25%的太阳电池；采用适合产业化生产的机械球磨和杂化墨水法结合硒化技术，制备出高质量CZTSSe薄膜和效率为4.22%太阳电池；阐明了球磨过程CZTS形成的机制，和CZTS硒化过程分层的结构及其对转变效率的影响；发现Mo(S,Se)2(MSSe)对转换效率的影响主要来自与CZTSSe形成的界面,而不是体电阻。通过优化CZTSSe薄膜和CZTSSe/MSSe界面质量，制备出效率为7.48%的太阳电池；.利用实验和第一原理计算，发现Cd与CZTS或Zn与CdS合金化能减少CZTS/CdS内建电场的晶格失配和能带失配，证明ZnO/CZTS界面能带排列为I型；发现贫Cd Cu2CdSnS4(CCTS)的本征缺陷主要是VCu和2CuCd-SnCd缺陷对，准化学计量比CCTS的本征缺陷主要是VCu和CuCd。CCTS的p型导电来自VCu受主的贡献,而2CuCd -SnCd缺陷使VCu数量增加，离化能降低，导致贫CdCCTS比准化学计量比CZTS的空穴浓度高，带隙小；发现In在CZTSSe掺杂时，大部分In取代Cu（InCu）和Sn（InSn）形成InCu-InSn施主缺陷，少部分In取代Zn形成InZn施主，缺陷种类与In的掺杂浓度有关。InCu-InSn和InZn施主对本征受主VCu和ZnCu补偿，导致CZTSSe空穴浓度随In掺杂浓度增加降低， CZTSSe太阳电池效率减小，但没有发生从p向n转型。.研究结果对通过调控本征缺陷，优化内建电场和背电极结构提高转换效率，发展无毒CZTSSe太阳电池制备技术有重要学术价值。