锰氧化物/石墨烯纳米复合导电性增强光吸收层的制备与光电转换性能研究

The novel solar cells with a special high efficiency solar energy absorption layer of organic metal halide perovskite have attracted much attention these 4 years. Such layers are made of CH3NH3PbI3 and its derivatives. However, these compounds show many shortcomings: chemical instability, short life, and poisonousness to environments due to Pb elements as well. Alkali element doped manganites(LaMnO3) are a kind of inorganic perovskite oxides of non-toxicity, high stability and narrow band energy gap near to that of CH3NH3PbI3. Although the carrier mobility of manganites is 1/3-1/4 times of CH3NH3PbI3, it can be improved by taking advantage of the ultra high carrier mobility of the reduced graphene after mixing with each other, which can enhance the carrier transportation in manganite. In this research project, a solvent thermal method or sol-gel method will be adopted to synthesize inorganic manganite nanoparticles with homogeneous size. The nanoparticles will be then mounted in the network of graphene after mixing via a chemical reaction to achieve a nano-composite and be used as high-efficiency light absorbing layer instead of CH3NH3PbI3. The nanoparticle embedded in the network of graphene is to enhance the carrier moving ability in the layer. Most of our efforts will be emphasized on pursuing an optimal weight ratio of the nanoparticles to graphene to get excellent photon absorption. After that, a new inorganic perovskite solar cell should be developed and its optical-electronic properties should be also investigated. The ultimate aim of the project is to provide a new way to offer a new substitution for CH3NH3PbI3 layer.

新型有机钙钛矿结构太阳电池因制作简便和高光电转化效率而备受重视。其光吸收层为铅碘甲胺及其衍生物，但化学性质不稳定，易对环境造成污染。钙钛矿锰氧化物是一类无毒、化学稳定性高的窄带隙无机氧化物材料，其带隙大小与铅碘甲胺非常接近，且可调。尽管锰氧化物的载流子迁移率是铅碘甲胺的1/3到1/4，但如果与二维石墨烯晶体适当混合，利用石墨烯极高载流子迁移率可以增强锰氧化物光生载流子在其中的输运能力。本课题采用溶剂热法或溶胶-凝胶法合成尺寸大小均匀、无机钙钛矿锰氧化物纳米颗粒，并将其与石墨烯按不同质量比镶嵌制备成复合物，研究不同质量比混合后对锰氧化物光生载流子输运性能的增强机理，包括载流子的在吸收层内部的电子输运、复合、界面散射等基本物理问题。在此基础上，寻求最佳质量比的纳米复合物来替代铅碘甲胺用作太阳能电池光吸收层，研发高光电转效率的太阳能电池，为有机钙钛矿结构太阳能电池光吸收层提供一种可能的新选择。

锰氧化物电磁特性丰富，制备出几种纯相的钙钛矿锰氧化物及其与碳材料（石墨烯、无定形碳等）复合物，研究其在染料敏化太阳能电池（DSSCs）中的光电转换性能及物理机制：.（1）采用溶胶-凝胶法制备出La1-xCaxMnO3(0.1x0.4)钙钛矿氧化物纳米颗粒。发现DSSCs的性能随着x的增加而提高，在x = 0.3时达到最佳。但La0.7Ca0.3MnO3（LCMO）纳米颗粒易团聚，引入石墨烯（rGO）成功合成出了LCMO@rGO纳米复合物。发现复合材料中的rGO纳米片具有双重作用：一是阻止LCMO纳米颗粒的团聚，使其均匀分散在rGO纳米片上，暴露更多的活性位点。二是用作电荷快速转移的高性能导电基底。二者协同，与LCMO纳米颗粒或rGO相比，对I3-离子的催化活性更高，电荷转移速度更快，导致以LCMO@rGO复合物为对电极材料，组装后的DSSCs的光电转化效率为7.45%，远高于单纯LCMO纳米颗粒的效率。.（2）在rGO材料中引入异质原子形成电子调制，提供更多的催化活性位点。将LCMO纳米颗粒和掺氮rGO复合，制备出LCMO@N-rGO复合材料，在I-/I3-离子的还原反应过程中展现出优异的电催化活性和较低的电荷转移电阻(Rct)。采用LCMO@N-rGO纳米复合材料做对电极的DSSCs光电转换效率达到7.9%，.（3）鉴于La0.67Ca0.33MnO3和N-rGO二者之间因协同效应是导致光电转换性能增强的根本原因，推广并设计经碳材料修饰后的复合体系。例如，对尖晶石型铁氧体Fe3O4材料，因其含Fe3+和Fe2+离子，发现该材料具有良好的导电性能和电催化性能；但该材料在纳米化合成期间易于团聚和氧化成Fe2O3而失去良好的导电性和电催化性能，通过与石墨烯和无定形碳的复合成功解决这些问题。二者协调效应导致光电转化效率远高于Pt的，达到10%。本工作将为高效、低成本的DSSC提供新思路。