有机／无机杂化钙钛矿光伏器件的电极修饰和性能提高

Organic/inorganic hybrids with the perovskite structure have strongly attracted the attention of the photovoltaic community due its achieved high conversion efficiency. In perovskite solar cell, the most used anode modulation material is oxide that acts both collecting electrons and blocking diffusion holes. However, the limited conductivity of oxide reduces the electron collection, furthermore decreases the conversion efficiency. Meanwhile， the external quantum efficiency of solar cells based on perovskite drops in the wavelength range of 500-800nm. Both above mentioned factors affect the achievement of higher conversion efficiency. In this project, an approach of electrode modulation is developed for the sake of improving the collection of electrons, in which TiO2-Ag hybrid nanocomposites, with the structure of single Ag nanoparticle on the individual TiO2 nanorod, is used to modulate cathode of perovskite soalr cells. The size of Ag nanoparticles on TiO2 nanorods can be precisely controlled by varying UV irradiation time and additive. Due to metal nanoparticle can act as a sink of photoinduced charge carrier, one Ag domain on TiO2 nanorod accumulates photoexited electons and provides a preferential site for continuous pathway of electron. Ag-TiO2 nanorods not only block diffusion hole like TiO2 nanoparticles, but also well transport the injected electron from perovskite active layer to cathode. Besides, the incorporation of plasmonic absorption could make up the external quantum efficiency drop in the wavelength range of 500-800nm. According to our plans, the photophyics progresses in provskite active layer and the interfaces will be investigated for the sake of better understanding perovskite semiconductors through the measurements of electric field modulated photoluminescence, transient photocurrent, UPS and so on. The plasmonic enhancement effect of nanoparticles on TiO2 rods will be demonstrated. The electric field treatment of perovskite semiconductors will be applied to the fabrication of perovskite active layer, which will result in the shift of moveable ions. The electric field induced shift of ion can produce the perovskite semicondutor with nonuniform distribution, which will change the photoelectric properties of perovskite matrials. This project is very important to improve the performance of perovskite solar cells.

有机/无机杂化钙钛矿太阳能电池由于其高转换效率引起太阳能电池界的广泛关注。但是，目前这种电池所用的电极修饰材料的电子收集效率并不是很高，外量子效率相应和太阳光谱匹配不是很好，器件性能还有提升空间。本项目将溶胶光催化合成技术制备的TiO2-Ag纳米棒用于钙钛矿太阳能电池电极修饰，提高电子收集效率。TiO2纳米棒上的银纳米粒子的大小可以通过紫外线照射时间和添加剂精确地控制。由于纳米银的能级位置，TiO2-Ag纳米棒上的银颗粒和电极之间可以形成很好的电子收集通道，使其在保留阻挡扩散空穴的基础上，更有效地收集电子。同时纳米银颗粒产生的表面等离激元效应还可以弥补钙钛矿材料在550-800nm波长范围的外量子效率出现下降问题。本项目将对发生在有机/无机杂化钙钛矿半导体材料的光物理过程进行详细研究，对钙钛矿光功能材料进行电场处理改性研究，对器件进行优化，使制备的太阳能电池的关键技术指标达到实际应用水平

钙钛矿太阳能电池在短短的几年间飞速发展，效率不断攀升。但是，其要想从实验室走向产业界，还需解决一些关键问题，如效率、稳定性、铅毒性和工作机理等。本研究针对钙钛矿太阳能电池存在的问题，在界面修饰、形貌的控制、无铅钙钛矿、钙钛矿材料物性和钙钛矿太阳能电池的工作机理几个方面开展研究。取得了一些有意义的研究结果。发现了TiO2电子传输层的光浸润效应和消除的方法。UV光照射可以改变TiO2薄膜的表面形貌，使其表面形成致密的微孔这些孔的存在将有利于钙钛矿层的附着特性。从器件I-V曲线我们可以看出没有经过UV处理的器件的I-V曲线有明显的S-型结构，说明在TiO2和钙钛矿界面有明显的势垒。随着在无氧环境下UV处理时间的增加，界面势垒降低，器件的S-型曲线减弱，最终消失。利用溶液工程方法和真空热退火法相结合控制钙钛矿薄膜的表面形貌和结晶度，通过优化的二元溶剂体积比和真空处理时间，我们制备出晶粒大、结晶好、表面平整的钙钛矿薄膜。二维钙钛矿是近年来公认的高效稳定钙钛矿太阳能电池材料，但是这种材料材料传输能力差。我们提出了一种简便的方法来制造紧凑、大颗粒、无针孔和结晶良好的二维/三维钙钛矿混合薄膜，以应用于具有高再现性的高效太阳能电池。首次将Diethylammonium bromide溶液用于钙钛矿太阳能电池中甲基碘化铵（MAPBI3）活性层的后处理和掺杂，其可以显著提高光电转换效率，从15%左右提高到19.7%。通过PbSCN和溴化阱掺杂客服了锡基钙钛矿材料结晶快和氧化，显著提高了非铅钙钛矿的光电转换效率。特别是纯锡基钙钛矿太阳能电池的光电转换效率达到6.6%。研究了MAPBI3薄膜的低温相变和光学特性的变化，发现了在其在低温下的带隙变化规律，计算出激子束缚能。发现开路电压over-shoot现象是由于钙钛矿半导体层内部的离子迁移造成的。离子迁移导致钙钛矿光功能层和电子传输层及空穴传输层界面的能带弯曲，能带弯曲导致光生载流子在弯曲部位发生聚集，使得载流子的运动方向和收集方向相反，降低了开路电压。

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