CH3NH3I在制备CH3NH3PbI(3-x)Clx钙钛矿太阳能电池中的作用

利用具有钙钛矿结构的有机-无机杂化卤化物制备的太阳能电池, 由于具有溶液可加工性和高光电转换效率, 受到了广泛关注. 在目前报道的最高光电转换效率的器件中, 采用了CH₃NH₃PbI_(3-x)Cl_x碘氯混合钙钛矿作为吸光层, 据报道在这种材料中光电子的扩散长度可以超过1 μm. 本文综述了在CH₃NH₃PbI_(3-x)Cl_x方面现有的研究工作, 指出了薄膜制备条件的重要性, 并研究了CH₃NH₃I在PbCl₂/CH₃NH₃I热解法制备CH₃NH₃PbI_(3-x)Cl_x吸光层中的作用. 扫描电子显微镜研究表明CH₃NH₃I加入量为PbCl₂的2倍到2.75倍时, CH₃NH₃I加入量的增加可以提高CH₃NH₃PbI_(3-x)Cl_x吸光层的覆盖度和结晶度, CH₃NH₃I加入量进一步增加到3倍时, 形貌变化不大. X射线光电子能谱的数据证实了CH₃NH₃I加入量对覆盖度的影响, 并显示在CH₃NH₃I加入量大于PbCl₂的2.5倍以后, CH₃NH₃PbI_(3-x)Cl_x中氯的掺入量急剧下降. 光电测试表明器件性能随CH₃NH₃I加入量增加而增加, 在CH₃NH₃I/PbCl₂为3/1时达到最高, 加入量略小于3/1对性能影响不大.

Effects of CH3NH3I on fabricating CH3NH3PbI(3-x)Clx p erovskite solar cells

Perovskite solar cell, which is prepared by using the organic-inorganic hybrid halide CH₃NH₃PbX₃ (X = I, Cl and Br), receives widespread attention because of its solution processability and high photon-to-electron conversion efficiency. The highest reported photon-to-electron conversion efficiency is that using CH₃NH₃PbI_(3-x)Cl_x as an absorber. It is reported that the diffusion length is greater than 1 micrometer in this mixed halide perovskite. The method most commonly used in preparing CH₃NH₃PbI_(3-x)Cl_x film is the one-step pyrolysis method, which has a complex reaction mechanism. In this paper, we review the work about CH₃NH₃PbI_(3-x)Cl_x perovskite, in which emphasis is put on the importance of the preparation process, and analyze the role of CH₃NH₃I in the one-step pyrolysis method for fabricating the CH₃NH₃PbI_(3-x)Cl_xperovskite layer. Scanning electron microscope images show that CH₃NH₃I can improve the coverage and crystallinity of the perovskite layer for precursors in low CH₃NH₃I concentrations (CH₃NH₃I/PbCl₂=2.0 and 2.5). For precursors in high CH₃NH₃I concentrations (CH₃NH₃I/PbCl₂=2.75 and 3), this change is not obvious. X-ray photoelectron spectroscopy confirms the change of coverage, and indicates that the content of Cl in CH₃NH₃PbI_(3-x)Cl_x will be less than 5% for precursors with high CH₃NH₃I concentrations (CH₃NH₃I/PbCl₂>2.5). Perovskite solar cells based on CH₃NH₃PbI_(3-x)Cl_x with different Cl dopant concentrations are studied by photoelectric measurements. Photocurrent density-photovoltage curves show that the performance of the devices increases with the increase of CH₃NH₃I concentration in precursors. And the incident-photon-to-current conversion efficiency (IPCE) measurements indicate that the devices fabricated by using precursors with high CH₃NH₃I concentration have a relatively high external quantum efficiency. These results imply that only CH₃NH₃PbI_(3-x)Cl_x with very low Cl dopant concentration will be effective material for photovoltaic application. To further understand the difference between these devices during working condition, transient photovoltage/photocurrent measurements are carried out to investigate the carrier dynamics in the device. Transient photovoltage decay curves indicate that high Cl dopant concentration may decrease the photoelectron lifetime in CH₃NH₃PbI_(3-x)Cl_x, and results in a relative low open-circuit photovoltage in the corresponding photovoltaic devices. The charge transport time in the devices of various Cl concentrations are studied by transient photocurrent decay method. CH₃NH₃PbI_(3-x)Cl_x with low Cl dopant concentration has relative short transport time, which can avoid the recombination process and increase the charge collection efficiency.