钙钛矿太阳能电池非规则界面载流子输运扩散机理研究

For all-solid-state planar organic-inorganic hybrid CH3NH3PbI3 solar cell, the typical structure consisted of ITO anode layer, TiO2 electron transfer layer (ETL), CH3NH3PbI3 layer, spiro-OMeTAD hole transfer layer (HTL), metal cathode layer. The interface between TiO2 ETL and CH3NH3PbI3 layer, as well as CH3NH3PbI3 layer and spiro-OMeTAD HTL was asymmetrical and irregular in crystal structure, geometry, electronic structure, and the other physicochemical property. It is easy for CH3+/NH2+/I- ion to diffuse into ETL and HTL, which could influence the physicochemical property of interface seriously. More important, the diffusion of above ion could result in the change of potential barrier of irregular interface. So it is important to research the diffusion mechanism of CH3+/NH2+/I- ion at irregular interface, as well as the carrier transport mechanism at irregular interface, both for fundamental research and practical application. In the project, CH4/NH3/I ion beam with low energy is used to react with the surface of ITO, TiO2, spiro-OMeTAD, CuI, and Al2O3 films, by which the diffusion of ions in films could be simulated. TEM and EELS techniques are used to study the diffusion of CH3+/NH2+/I- ion at amorphous, grain boundary, and grain. KFM and C-AFM techniques are used to study the influence of CH3+/NH2+/I- ion diffusion on the electro-optical property along the normal direction of surface. The diffuse-transmission model and ballistics-diffuse model are used to calculate the CH3+/NH2+/I- ion diffusion and carrier transport mechanism at irregular interface, amorphous parts, grain boundary, and grain. Based on the results of TEM, EELS, KFM, and C-AFM, set the diffuse-transmission model as the necessary supplement of ballistics-diffuse model, and the boundary conditions could be self-consistent and chimed each other. Through the project, the diffusion mechanism of CH3+/NH2+/I- ion at irregular interface, as well as the carrier transport mechanism at irregular interface, could be deduced by the analysis of experiment result and theory model.

全固态平板型有机-无机杂化钙钛矿CH3NH3PbI3类太阳能电池结构中存在多种非规则界面结构，因此，载流子在非规则界面处的输运扩散问题，成为该领域研究热点。本项目利用低能CH4/NH3/I离子束与不同功能层表面相互作用，模拟CH3+/NH2+/I-离子基团在不同功能薄膜表面的扩散过程；利用TEM/EELS分析CH3+/NH2+/I-离子基团在不同晶面方向的扩散；利用KFM和C-AFM分析CH3+/NH2+/I-离子基团的扩散对非规则界面处界面势垒及光电性能的影响规律；以扩散-透射理论模型和弹道-扩散理论模型分别模拟CH3+/NH2+/I-离子基团在非规则界面处及在不同晶面方向的扩散，根据XPS/EELS/KFM/C-AFM结果，确定两种模型各自的边界条件，并以扩散-透射理论模型对弹道-扩散理论模型进行必要补充，最终在实验和理论两方面揭示载流子在钙钛矿太阳能电池非规则界面处的扩散机理。

平面异质结结构的有机无机杂化金属卤化物钙钛矿太阳能电池具有制备工艺简单、光电转换效率高等优点。但是，其电子传输层制备工艺中一般含高温退火工艺，这严重增加了制备成本，也抑制了钙钛矿太阳能电池在柔性基底上的应用。因此，开发电子传输层全室温制备工艺显得非常重要。本项目中，以传统的甲氨铅碘(CH3NH3PbI3, MAPbI3)为光电转换材料，利用直流脉冲磁控溅射方法在室温条件下制备TiO2电子传输层，并制备MAPbI3钙钛矿太阳能电池器件。作为参比对象，利用传统的溶胶凝胶方法制备TiO2电子传输层及MAPbI3钙钛矿太阳能电池器件。研究结果表明，利用直流脉冲磁控溅射方法制备TiO2电子传输层，在非退火条件下，直接进行MAPbI3太阳能电池器件制备，实现16.1%的光电转换效率和14.9%的迟滞系数；而相同条件下溶胶凝胶500℃退火制备的MAPbI3太阳能电池器件，其光电转换显效率仅为13.4%，迟滞系数高达38.5%。相比较于溶胶凝胶TiO2电子传输层器件20.08 mA/cm2 的电路电流，直流脉冲磁控溅射TiO2电子传输层器件的短路电流可提升至20.08 mA/cm2。直流脉冲磁控溅射TiO2电子传输层的表面电势为(4.81±0.04) eV，溶胶凝胶TiO2电子传输层的表面电势为(4.66±0.01) eV，因此直流脉冲磁控溅射TiO2电子传输层的导带底低于溶胶凝胶TiO2电子传输层，这有利于光生载流子向直流脉冲磁控溅射TiO2电子传输层进行输运。直流脉冲磁控溅射TiO2电子传输层的R_s^EIS值仅为35.95 Ω•cm2，而溶胶凝胶TiO2电子传输层的R_s^EIS值达到55.45 Ω•cm2。 根据上述研究结果，建立光生载流子在直流脉冲磁控溅射TiO2电子传输层和溶胶凝胶TiO2电子传输层中的输运模型。就直流脉冲磁控溅射TiO2电子传输层而言，由于导带底位置低于溶胶凝胶TiO2电子传输层，因此有利于光生载流子向电子传输层注入；同时，沿截面方向的链状纳米晶结构，可有效提高光生载流子沿最短输运路径输运至导电电极的概率，因此基于直流脉冲磁控溅射TiO2电子传输层的MAPbI3太阳能电池器件服役性能优于基于溶胶凝胶TiO2电子传输层的MAPbI3太阳能电池器件。最终在实验和理论两方面揭示载流子在钙钛矿太阳能电池电子传输层表界面处的扩散输运机理。

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