双量子点-染料复合敏化ZnO纳米管光阳极的构筑及其光伏性质研究

Quantum dot sensitized solar cells (QDSSCs) have attracted extensive interest as a novel type of nanostructured solar cell. For practical applications, the energy conversion efficiency of QDSSCs requires further improvement. It has been proved that co-sensitization is an effective strategy for enhancing the photoconversion efficiency. It consists of two quantum dots (QDs) with different absorption regions which extend the photoresponse of the semiconductor anode into the visible region. However, the two QDs are usually sequentially assembled onto an semiconductor anode film, forming a cascade (QDs a/QDs b/ semiconductor layer) co-sensitized structure. Thus, the injection of an excited electron from the outer layer (QDs a) to semiconductor is less efficiently because the excited electron will be easier to be captured or recombined by the QDs of inner layer (QDs b)in the cascade structure. In this project, we develop a unique QDs/nanotube/QDs QDSSC configuration based on ZnO nanotube (NT) array, which employs the sensitization of the inner wall surface and outer wall surface of the ZnO NT with different QDs, respectively. The deposition of the two kind of QDs on the different walls is advantageous to the electron injection and hole-recovery of QDs. Then, dye will be adsorbed on the quantum dots sensitized ZnO nanotube array. An improvement of the photo-conversion efficiency will be expected by tuning the light harvesting via size and kind control of QDs. In this project, the effect of morphology of ZnO, QDs on photovoltaic and photoelectrochemical performance will be investigated. And the performance of the space charge layer between the QDs and semiconductor film will be studied. In addition, the relationship between the defect state energy level, surface state density, defect states at the interface and the size, load density of QDs on the ZnO NT will be explored. The results will provide new insight on the fabrication of high efficiency photoanode in QDSSCs.

量子点敏化太阳电池属新型纳米结构电池。复合敏化能够提高其能量转换效率，但目前提高的程度有限，原因是现有光阳极均采用叠层结构（量子点a/量子点b/半导体）。对于这种结构，外层量子点a的光生电子经量子点b向半导体传输时，易被各种陷阱捕获，降低电子传输效率，导致转换效率低。本项目拟探索一种改进方法，主要研究内容有以下三方面：1.用ZnO纳米管阵列构筑“三明治”型光阳极新结构（量子点a/ZnO半导体/量子点b），显著降低光生电子-空穴对复合，再用染料进行敏化，扩大光阳极的光吸收频谱范围，从而提高能量转换效率；2.研究ZnO纳米管形貌、量子点配对等对电池光伏和光电化学性质的影响，优化光生电子注入、复合和输运等动力学参数；3.探索量子点中缺陷态能级、态密度、界面缺陷等与其尺寸、负载密度等的关系，揭示量子点/半导体纳米结构界面电子的传输机制。本项研究旨为提高量子点敏化太阳电池能量转换效率提供一种新方法。

量子点敏化太阳能电池是一种新型纳米结构电池，其光阳极主要由宽带隙、具半导体性质的氧化物（TiO2, ZnO, SnO2）和量子点构成，提高电池的转化效率是目前研究的重点。研究表明，复合敏化以及构建新颖的电池结构是提高转换效率的两个重要途径，复合敏化有利于扩展吸光范围，而构建科学的电池结构可以减少光生电子的复合、提高电荷传输效率。本项目主要从以下几个方面开展了研究工作：（1）将比表面积较大、传输电子快的一维阵列（纳米管、纳米棒等）作为电子传输层；在ZnO与敏化剂之间引入复合阻挡层或者对量子点进行掺杂，改变能带结构，提升电荷转移、传输与分离效率；对敏化剂表面进行改性，提升空穴提取能力；（2）构建散射能力梯度上升的新型结构光阳极，在光阳极中引入具局部表面等离子体共振效应的纳米材料以使更多的光激发染料、增大染料吸附面积等从而产生更多的光生载流子，大幅提高电池转换效率；（3）探索多种电化学性能优异的新型纳米材料的制备与应用。通过项目组研究，获得以下重要成果：（1）建立了双量子点、染料复合敏化ZnO纳米阵列光阳极制备新路线，获得转换效率较高的ZnO基复合敏化太阳能电池；研究了量子点/ZnO界面的势垒、量子点能级结构中的缺陷能级等，揭示了电子的传输机制；（2）提出了一种空间约束应变驱动的方法首次制备了低温纯相单斜CsPbBr3全无机钙钛矿，所制备电池最高PCE为7.52 %，迟滞因子为0.024 (所报溴铅铯文章中最小)，在不含界面修饰的光电器件中，创造了开路电压 (VOC)记录值为1.4602 V，这种方法有助于应用到其他低对称钙钛矿的应用当中，具备很大的潜力；（3）高电子迁移率的一维ZnO阵列用于碳基无空穴传输层钙钛矿电池，成本低，发展了一种具有良好钙钛矿相容性和高柔性的低温碳电极在钙钛矿电池的应用方法，对于今后钙钛矿太阳能电池高效低成本的生产提供了思路，具有重要的意义。