基于胶体纳米棒阵列异质结结构的可控构筑及其界面电荷输运机制的研究

Interfacial charge transport properties of nanorods plays decisive role in determining the photovoltaic characteristics of solar cells. The surface/ interfacial defect states of CdS nanorods serve as charge traps and seriously prevent interfacial charge transport, which has become a main limiting factor in improving the efficiency of photovoltaic cells based on nanorods. This project builds on previous studies of the self-assembly of CdSe quantum dots and CdSe @ CdS composite nanocrystals, the CdS nanorods arrays will be fabricated on solid conductive substrates based on a combination of thermal annealing technique and the thermal properties of surface organic ligands, and then CdS/Cu2S heterojunction structure is fabricated via the ion-exchange technique. Thermal properties of organic capping ligands is studied by thermogravimetric analysis and infrared spectroscopy, the formation mechanism of nanorods arrays is fabricated by considering several factors, such as nanorods sample, annealing condition, various forces in the self-assembly system. The interfacial charge transport behavior of nanorods arrays and its heterojunction is mainly studied by transient surface photovoltage technique, an optimized method of reducing the charge recombination of photo-generated charge and improving its transport properties is proposed; and the model for describing the relation between the heterojunction structure and its photovoltaic properties is also set up. This study provides the theoretical and technical basis for effectively solving the problem of interfacial charge recombination and improving the charge transfer properties, which is meaningful for enhancing the efficiency of the photovoltaic cells based on nanocrystals.

纳米棒界面电荷的传输特性对其光伏电池的光电性能具有决定性的影响。CdS纳米棒的表/界面缺陷态容易成为电荷复合陷阱而严重影响界面电荷的传输，成为抑制其光伏电池效率提高的瓶颈问题。在前期对CdSe量子点和CdSe@CdS纳米晶自组装的研究基础上，本项目结合表面有机配体的热学特性和退火技术在固体导电基底上构建CdS纳米棒阵列；并利用离子交换技术构筑CdS/Cu2S异质结结构。采用热重分析和红外光谱测试技术研究表面有机配体随温度变化的规律；建立纳米棒、退火条件、自组装体系中各种作用力等对纳米棒阵列结构的影响机制；通过瞬态表面光伏技术对CdS纳米棒阵列及异质结界面电荷输运行为进行研究，提出降低光生电荷复合和提高电荷传输性能的优化方案，并建立异质结微观结构与光电性能关系模型。该项目为有效解决纳米棒界面光生电荷的复合难题和提高界面电荷传输性能奠定理论和技术基础，对提高纳米晶光伏电池效率有重要的意义。

纳米棒界面电荷的传输特性对其光伏电池的光电性能具有决定性的影响。然而胶体纳米棒的表/界面缺陷态容易成为电荷复合陷阱而严重影响界面电荷的传输，成为抑制其光伏电池效率提高的瓶颈问题。本项目首先利用种子生长法合成尺寸和形貌均一的核壳结构CdSe/CdS纳米棒，并采用热重分析和红外光谱研究分析了纳米棒表面有机配体的热力学性质，结果发现退火前后包覆在纳米棒表面的有机分子及络合物有很大程度的减少；其次，结合纳米棒表面有机配体的热学特性和退火技术在固体导电基底（Si、TEM微栅）上构筑多种CdSe/CdS纳米棒阵列结构（单层、多层、平行和垂直排列等）；同时，利用离子交换技术构筑CdS/Cu2S异质结结构，通过调控铜盐的浓度、Cd2+/Cu+摩尔比、浸泡时间等参数达到了控制异质结交换程度的效果，并利用EDS对CdS/Cu2S异质结阵列进行元素分析，实验结果显示，离子交换技术可以成功构筑CdS/Cu2S异质结结构和可控调节异质结的组分；最后采用表面光伏技术对纳米棒阵列与固体衬底界面电荷输运行为进行研究，验证了利用退火技术获得自组装结构的同时，又解决了纳米晶材料表面所包敷的有机配体分子造成纳米晶材料电荷传输性能不佳的问题，也起到了降低光生电荷复合和提高电荷传输性能的目的。该项目为有效解决纳米晶界面光生电荷的复合难题和提高界面电荷传输性能奠定理论和技术基础，对提高纳米晶光伏电池效率有重要的意义。