基于Zn(O,S)缓冲层的Cu2ZnSn(S,Se)4薄膜太阳电池界面能带匹配和缺陷钝化研究

Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells are attracting considerable attention in recent years. However, a major hindrance to the efficiency of CZTSSe based solar cells is the large open-circuit voltage (Voc) deficit when compared to the band gap of the absorber. Interfacial recombination especially at the absorber/buffer interface is an important factor that limits the Voc. CdS as a conventional buffer layer, however, has some drawbacks, undesired low band gap, toxicity, and an inappropriate conduction band alignment of the CdS/CZTSSe interface. An alternative buffer layer, ultrasonic spray pyrolysis Zn(S,O), is proposed to replace CdS. Two ways of interface engineering approaches are simultaneously explored to improve CZTSSe based solar cell performance. First of all, conduction band offset is optimized to achieve a more favorable band alignment between buffer and absorber by tuning the O/(O+S) ratio in the Zn(S,O) film. Secondly, a thin layer of ZnS nanodots with adjustable spacing, which not only serves as the passivation layer to reduce the interface recombination but also enables the lateral diffusion of charge carriers, is introduced to the interface between CZTSSe and Zn(S,O). Band alignment amendments and elimination of interface defects are integrated to eradicate interface-related Voc bottleneck. Last but not least, an in-situ mass spectrum is carried out to provide more insight into the pyrolysis process in order to study the kinetics and thermodynamics during the film deposition. The success of the project will make a great contribution to the achievement of high-efficient, low-cost, long-life and environment-friendly CZTSSe solar cells.

Cu2ZnSn(S,Se)4 (CZTSSe) 薄膜太阳电池是当前研究热点，其面临的主要瓶颈问题是开路电压损失大，其中缓冲层/吸收层的界面复合是限制开路电压的重要因素。传统缓冲层CdS与CZTSSe异质结界面能带匹配度不高，且带隙窄，毒性大。本项目提出利用喷雾热分解Zn(O,S)取代CdS，通过界面能带匹配和缺陷钝化获得优异的无镉缓冲层。一方面调控Zn(O,S)薄膜的O/(O+S)比例，优化Zn(O,S)/CZTSSe异质结界面能带匹配；另一方面利用ZnS量子点为钝化层，调控点间距，既钝化界面缺陷中心，又保证载流子自由传输。两种界面调控手段双管齐下，协同解决瓶颈问题，以期减少界面复合，获得高效无镉CZTSSe太阳电池。同时结合原位质谱，对热分解过程进行在线研究，阐明前驱体分解的热力学原理和薄膜生长动力学规律。该项目的成功将促进实现真正意义清洁、高效、低成本CZTSSe薄膜太阳电池的目标。

Cu2ZnSn(S,Se)4 (CZTSSe)薄膜太阳电池缓冲层/吸收层异质结界面复合导致开路电压损失较大，本项目针对这一固有瓶颈问题出发，提出利用界面调控的手段获得优异的无镉缓冲层。首先，采用喷雾热分解法制备出成分可控Zn(O,S)薄膜，该薄膜具备能带可调、附着力好、光透过率高等作为缓冲层所要求的特点。同时，借助现场质谱，采集热分解过程成分变化信息及追踪中间生成物，结合对某些前驱体的理化特性了解，提出了质子促进热分解机理。该机理的研究有助于优化Zn(O,S)薄膜的生长条件，实现对薄膜生长的可控制备，获得高质量薄膜。另外，对喷雾热分解技术进行了扩展与应用，证实了该技术在制备过渡金属磷化物的普适性，并成功应用于钠离子电池负极材料。通过电子-离子双连续的三维多孔结构的设计，该材料展现出了优越的倍率和循环稳定性。最后，采用溶液法成功制备性能优异的CZTSSe吸收层，转换效率达到了8.6%，同时利用ZnS量子点为钝化层，以期减少界面复合提高电池性能，并采用同步辐射研究钝化层对界面的影响。该项目为进一步实现太阳电池流水线规模化生产奠定基础，可实现真正意义上绿色清洁、环保可再生的能源。