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钙钛矿基有机-无机杂化材料光/电性能研究
赵鹏君
学位类型博士
导师徐金宝
2015-05-24
学位授予单位中国科学院大学
学位授予地点北京
学位专业材料物理与化学
关键词铁酸铋 有机-无机杂化钙钛矿 锰酸钙 自发极化 光电性能
摘要

以甲胺基卤化铅CH3NH3PbX3(X= Cl,Br,I)为代表的有机-无机杂化钙钛矿材料是近年来一种新兴的光电转换材料,其具有制备温度低,成本相对低廉,器件光电转换效率高等优点。目前,杂化钙钛矿基太阳能电池的最高效率已经超过20%,使其超越了传统的染料敏化太阳能电池和有机太阳能电池,成为最具实用化前景的第三代薄膜太阳能电池。但是,作为一种新型材料,对于其基本物理性质和器件设计原理方面的研究目前相对欠缺。首先,尽管晶胞中存在有机基团,但其结构框架仍属于钙钛矿结构,传统无机氧化物钙钛矿所具备的一些基本性能,例如铁电性、自发极化行为等尚未进入杂化钙钛矿材料的研究范畴;其次,在器件结构设计方面,目前没有专门针对杂化钙钛矿太阳能电池器件的独立设计思路,多数杂化钙钛矿基光电转换器件沿用染料敏化或有机光伏器件的结构和制备工艺。 针对上述问题,本文从以下几个方向进行了系统研究: 1.利用压电探针显微镜观测了CH3NH3PbI3薄膜材料的原位自发极化行为,并绘制了该材料的电滞回线,进一步研究发现,CH3NH3PbI3薄膜材料的表面电畴在± 10V的外加偏压下能够实现180°反转。证明了该材料在室温下具备自发极化的能力,为铁电体材料,并且认为CH3NH3PbI3材料的自发极化一方面源于其四方相的晶体结构,另一方面与Pb2+和N3+具备的孤电子对密切相关。这一发现有助于利用现有的无机钙钛矿极化理论对有机-无机杂化钙钛矿器件的光电性能进行理论分析。2. 采用化学溶液沉积法制备了BiFeO3-CH3NH3PbI3复合全钙钛矿型光电器件,研究了其在可见光辐照下的I-V特性曲线。发现复合薄膜器件的开路电压Voc高达1.62 V,短路电流密度为 1.74mA·cm-2,光电器件的转化效率约为1.41 %。上述器件各项参数中,开路电压的值在目前所有太阳能电池器件中处于较高的水平。对光电压较高的原因进行了探索,一方面,BiFeO3和CH3NH3PbI3的表面电势(功函数)之间存在一定的势垒,能够提高器件电压,另一方面,复合器件的表面表现出高度一致的自发极化现象,表明偶极子的排布较为规则,该性质也能提高器件的开路电压。此外,对单一BiFeO3、CH3NH3PbI3和BiFeO3-CH3NH3PbI3复合薄膜的XRD图谱进行比较,BiFeO3衬底能够对CH3NH3PbI3的结构起到稳定作用。本研究为设计新型的全钙钛矿型光电器件提供了新的思路。 3. 设计了全钙钛矿型的热电-光伏复合器件,该器件以CaMnO3和CH3NH3PbI3为主要材料。其中,CaMnO3既作为热电功能材料,又作为杂化钙钛矿基光电器件的电子传输材料。采用激光脉冲沉积法制备了锰酸钙薄膜,对其能带结构、光学性能、自发极化行为进行了系统研究。结果表明,锰酸钙薄膜的禁带宽度为1.75 eV,价带位置与TiO2相近,与CH3NH3PbI3匹配后能够吸收更多可见光的同时,有效促进光生载流子向相反方向迁移,其热电性能还能够吸收杂化钙钛矿材料在光子辐照下的声子振动能量,增强杂化钙钛矿的热稳定性;同时,锰酸钙表面具备很强的自发极化效应,有望起到与铁酸铋相似的增强开路电压的作用;此外,光学椭偏拟合图谱表明锰酸钙薄膜显示出很高的吸收系数和较低的光导,表明该材料是一种良好的窗口材料。 4. 利用单一溶液法制备了大尺寸CH3NH3PbBr3十面体晶体。该晶体尺寸为14×14 mm。单晶衍射结果表明,该晶体结构属立方相结构,空间群为P-43m(215),多晶衍射图谱与单晶结构模拟图谱高度一致。测量了该晶体在5 mW/cm2光照环境和暗态下的一系列物理性能。其中,发现单晶表面偶极子的排列与光照呈现出明显的相关性,表明外加光照能够诱导偶极子有序排布;光照后,由于光生载流子在偶极子定向排列产生的微电场作用下运动,使得样品表面的功函数发生了约200 mV的迁移,这一性质有利于提高宏观器件的开路电压;另外,光照下电流值约为暗态电流的20 倍,且在测试视野范围内无明显衰减现象。上述研究结果表明,对于杂化钙钛矿材料而言,单晶材料有望达到比目前广泛采用的纳米晶器件更高的光电转化效率。

其他摘要

Owing to the low-temperature preparation, low cost and high photoelectric conversion efficiencies, the inorangic-orangic hybrid perovskite materials, CH3NH3PbX3(X= Cl, Br and I), have beenregarded as kin of emerging photovoltaic materials. Up to now, the efficiencies record of perovskite solar cells is over 20%.Perovskite solar cells have surpassed dye-sensitized solar cells (DSSCs) and the organic photovoltaics (OPVs), and become the most promising candidate for the third generation solar cells. Despite all this, there are plenty of research works need to investigate on this innovative material, especially for the basic physical properties and device design principle. Firstly, as a kind of perovskite structured substance, some intrinsic properties in traditional inoranic perovskite, such as spontaneous polarization and ferroelectricity, have not come into the research category of hybrid perovskite materials. Secondly, the present device strucure of hybrid perovskite solar cells is based on that of the DSSCs and OPVs, and there is no independent devicedesign module specialized for hybrid perovskite solar cell devices. This dissertation aims at the problems above, and carry out theresearch work from the following several directions: (1) Surface spontaneous polarization behaviors as well as ferroelectric hysteresis loopof hybrid perovskite CH3NH3PbI3 film were confirmed by in situ PFM. The film’s ferroelectric domains can be inversed by bias voltage of ± 10V.The above observation confirms that the CH3NH3PbI3 filmis ferroelectric at room temperature. We attribute the spontaneous polarization behaviors of hybrid perovskite to the tetragonal phase and lone pair electrons in Pb2+ and N3+ cations. This report will facilitate understanding of the instinct physicalessence of hybrid perovskite solar cells. (2)Inorganic-organolead halide perovskite CH3NH3PbI3 modified BiFeO3 polycrystalline film hasbeen established through a chemical solution deposition method. The composite photoelectrode presents much larger open voltage and severalmagnitudes superior photoelectric conversion performance in comparison to the ordinary BiFeO3polycrystalline film. The I-V curve under visible light shows that the short-circuit current (Jsc) is 1.74mA?cm-2 andopen-circuit voltage (Voc) is 1.62V, the device’s photon to current efficiency is 1.41 %. Thelarge open voltage a is believed to attribute to the spontaneouspolarization of composite perovskite induced by BiFeO3 lattice and modified reduced workfunction of the modified BiFeO3 surface. In addition, BFO isable to provide the lattice matching substrate for orientedgrowth of the modified CH3NH3PbI3 and stabilize the crystalline structure of CH3NH3PbI3. Our results clearly provide novel sight to the device structure of hybrid perovskite based solar cells. (3) Hybrid halide perovskite photovoltaic-thermoelectric device based on CaMnO3and CH3NH3PbI3 was designed. In the device, CaMnO3 thin film is utilized as both the buffer layer for photovoltaic device and the thermoelectric function layer. Locations of the conduction band and the valence band, spontaneous polarization performance, andoptical properties were investigated. Results indicate the energy band of CaMnO3is 1.75 eV, and the location of the valence band is near to that of TiO2, which can match upwell with that of CH3NH3PbI3 on separating electron-hole pairs.More importantly, benign thermoelectric properties enable CaMnO3 film to assimilate phononvibration from CH3NH3PbI3.In addition, the consistentpolarization angle helps enlarge the open-circuit voltage of the composite system. Besides,CaMnO3 film shows large absorption coefficient and low extinction coefficient under visibleirradiation, demonstrating high carrier concentration, which is beneficial to the current density. In addition, the CaMnO3 thin film has high absorption coefficient and low optical conductivity, making it be a promising candidate as a window material for hybrid halide perovskit

文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4247
专题材料物理与化学研究室
作者单位中国科学院新疆理化技术研究所
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赵鹏君. 钙钛矿基有机-无机杂化材料光/电性能研究[D]. 北京. 中国科学院大学,2015.
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