量子点敏化p-型太阳能电池的构建、载流子传输机制及抑制电荷复合研究

Replacing the organic dye with semiconductor quantum dots to develop quantum dots sensitized p-type solar cells (p-QDSC) is the reasonable and effective approach to solve the two main problems existing in dye-sensitized p-type solar cells (p-DSC), that is, low dye adsorption and the low charge separation efficiency, which greatly limit the photocurrent of p-DSC. The aim of this project is focused on the construction, charge transport mechanism study and charge recombination suppression of p-QDSC. There are three main themes within the proposed research. The first is to construct p-QDSC prototype based on CdS quantum dots/p-type NiO film/iodine-free electrolyte system, and interpret the effect of key material, e.g., the electrolyte type, the NiO thin film thickness, and CdS quantum dot loading, etc. on the overall conversion efficiency to optimize the structure of p-QDSC. Secondly, the dynamics in the process of charge generation, diffusion, recombination, and collection and their competitive relationship will be studied, using intensity modulated photocurrent spectroscopy/intensity modulated photovoltage spectroscopy (IMPS/IMVS) analysis and electrochemical impedance spectroscopy (EIS) fitting. On this basis, studies will be done to explore new methods to improve the photovoltaic performance of p-QDSC. Various charge recombination suppression strategies, e.g., reducing the surface states, energy level alignment, and reducing the reactivity will be applied to the key surface area where recombination occures, e.g., the surface of quantum dots, the surface of NiO, and the surface of conductive substrate. This study is expected to be the foundation and the key to boost major breakthrough for pn-type solar cells and contributes to the fundamental research and technological applications of other new types of solar cells.

染料吸附量低和电荷分离效率低是导致目前染料敏化p-型太阳能电池光电流低的主要因素，以半导体量子点取代有机染料作为敏化剂，发展量子点敏化p-型太阳能电池是解决该问题的合理途径。本项目以CdS量子点/p-型NiO薄膜/非碘电解液体系为基础，构建量子点敏化p-型太阳能电池原型，揭示关键材料的组成、结构等对光电性能的影响规律，优化器件结构；建立初步的载流子传输理论模型，采用强度调制光电化学谱分析和电化学阻抗谱拟合等方法，系统研究载流子传输、复合、收集的动力学过程及相互竞争机制；在此基础上，探索提高光电性能的新方法，通过减少表面态、调整能带和降低反应活性等策略，抑制关键表面区域的电荷复合，获得高性能的p-型量子点敏化太阳能电池。本项目旨在提高p-型敏化太阳能电池的光电流，使之能够与n-型敏化太阳能电池相匹配，为高效pn-型敏化太阳能电池及其它高层次太阳能光电转换器件的设计制备提供实验基础和理论依据。

本课题通过以半导体量子点取代有机染料作为敏化剂，构建了新型太阳能电池结构，以解决染料吸附量低和电荷分离效率低的缺陷，提高敏化p-型太阳能电池的光电流。首先分别制备了CdS、CdSe等量子点和p-型NiO介孔薄膜，并主要以S2-/Sx2-为电解液体系，构建了三明治结构的量子点敏化p-型太阳能电池原型，系统研究了关键材料的组成、结构等对光电性能的影响规律，优化了器件结构；进而通过各种分析手段研究了载流子传输、复合、收集的动力学过程及相互竞争机制，研究表明造成光电流损失的主要原因是导电基底与电解液界面、介孔薄膜与量子点界面的电荷复合；在此基础上，研究了通过在导电基底上制作NiO致密层，阻断堆积在导电基底上的电子与电解液的反应；通过Cu2+掺杂提高NiO介孔薄膜载流子传输性能；通过ZnS、SiO2等对NiO多孔薄膜进行表面钝化；TiO2、ZnS等CdS量子点进行表面缺陷掩埋等策略，对关键表面区域的电荷复合进行抑制，提高了p-型量子点敏化太阳能电池的光电性能。然而，由于敏化p-型太阳能电池内部存在着多个关键的表面区域以及复杂的电荷复合行为，以及p-型光阴极的光电流失配，造成了严重的光电压和光电流损失，其存在问题基于现有的材料制备方法和界面理论很难得到理想的解决，而通过减少原设计电池内部的界面和材料，以减少电荷复合途径，是目前针对该电池结构的有效手段。研究后期，初步尝试设计开发了无电解液量子点敏化pn-型太阳能电池，减少了电池内部的传荷界面和电荷复合路径，为高效pn-型敏化太阳能电池及其它高层次太阳能光电转换器件的设计制备提供实验基础和理论依据。