MAxFA1-xPbI3 型钙钛矿材料的光学性质及结构相变研究

OPTICAL PROPERTIES INVESTIGATION AND STRUCTURAL PHASE TRANSITIONS OF MAxFA1-xPbI3 PEROVSKITE MATERIALS

庞国涛

11749239

硕士

物理电子学

陈锐

2019-05-24

2019-07-10

哈尔滨工业大学

深圳

钙钛矿作为一种新型光电材料，近年来愈发受到广泛的关注。卤素阴离子钙钛矿因其具有较大的吸收系数，较长的载流子扩散长度以及寿命而成为研究的重点。其中，碘离子钙钛矿因其较小的禁带宽度而成为制作钙钛矿太阳能电池的首选材料，目前钙钛矿太阳能电池的光电转换效率已经突破24%，这意味着在效率上钙钛矿太阳能电池已经满足了商用的条件。但是，钙钛矿材料的光学和电学稳定性极易受到周围温湿环境、光照条件等的影响，相关的器件只能在实验室中实现，距离真正的商用还有一段距离。因此，钙钛矿稳定性提升的相关研究成为该领域的热点。本文主要研究了MAxFA1-xPbI3（MA：CH3NH3+，FA：CH(NH2)2+）型钙钛矿材料光学性质及其结构相变。首先通过X射线衍射（XRD）测试确定了室温下样品均为立方相。之后利用变温（30 K ~ 295 K）光致发光测试，并结合低温以及室温的变激发功率光致发光光谱，对A位阳离子（MAxFA1-x）在钙钛矿材料发光过程中的影响进行了分析。为了解钙钛矿材料相变规律，定义了各样品的相变区间，并对各样品单位温度范围内的相变量（∆E/∆T，E为相变区间内发光峰峰位变化量，T为温度）进行了比较。研究发现，在同一温度下，当A位阳离子中FA越多时，材料的带隙越小。MA与FA的比例与带隙变化之间大致呈线性关系，但这种情况只在A位阳离子为混合状态的情况下才成立。对于纯的MAPbI3和FAPbI3，其带隙偏离了这种线性关系。A位阳离子对钙钛矿的光学性质影响非常大，当MA与FA的比例相当的时候，温度升高，发光峰的红移范围最大；而当MA和FA中任意一个占主导作用时，发光峰的红移范围会缩小；在样品中只有MA或者FA时，材料的红移过程从缓变转变为突变。这种在变温过程中发光峰的红移范围即为钙钛矿材料的相变区间。对这种相变的变化分析发现，当MA与FA比例相当时，随温度变化，钙钛矿材料具有最好的相稳定性；而当MA或者FA中的某一种阳离子占据主导时，材料最不稳定。这种稳定性来源于晶体内部的应力作用。MA与FA由于尺寸不同而引起的两种不同趋向应力的同时存在使得晶格不容易发生扭曲，从而在光谱上表现出最平缓的红移。上述结论对深入理解钙钛矿材料光学性质和结构相变稳定性至关重要，对于解决钙钛矿材料相稳定性问题，推动基于钙钛矿材料光电器件性能的提高有着重要的指导意义。

Recently, as a new type of opto-electronic material, halide perovskite has large absorption coefficient, long carrier diffusion length and long carrier lifetime and, thus, it becomes the focus in the research field. Lead perovskite has become the mostly investigated material for solar cell due to its narrower bandgap. So far, the power conversion efficiency of perovskite solar cell has exceeded 24%, which means that it is appropriate for commercial use in this respect. However, its optical and electrical properties could be severely affected by the temperature, humidity and light amid the environment. Therefore, the research of stability improvement of pervoskite has been the hot spot in this field.In this thesis, the optical properties and structral phase transitions of MAxFA1-xPbI3 (MA：CH3NH3+, FA：CH(NH2)2+)have been investigated. Samples used herein are confirmed to be cubic phase according to XRD characterization firstly. The influence of A site cations (MAxFA1-x) on the optical properties has been investigated by analyzing the temperature dependent (30 K ~ 295 K) photoluminescence spectra and excitation power dependent photoluminescence spectra at low and rome temperature. To explore the phase transitions in perovskite material, phase transition range has been defined, and the phase transition per unit temperature (∆E/∆T, E here is the peak position changes in phase transition range, T is temperature) has been compared.It is found that the bandgap of MAxFA1-xPbI3 become narrower as FA increase. The ratio of MA to FA is linearly related to the bandgap of MAxFA1-xPbI3 except for the pure A site cation conditions. Bandgaps of MAPbI3 and FAPbI3 diviate from this trend actually. The type of A site cation has significant impact on temperature dependent photoluminescence spectra of MAxFA1-xPbI3. It demonstrates the largest red shift of photoluminescence peak while the proportions of MA and FA are comparable when the temperature increases; the red shift range will shrink if either of the two kinds of cations dominant in the structure; MAPbI3 and FAPbI3 display abrupt phase transitions compared to the mixed A site cation perovskites. The red shift range here can be used to define the phase transition region. Analyses of phase transitions show that perovskites possess best stability if proportions of MA and FA are comparable; and the materials display poor stability while either of the two kinds of cations dominants in the structure. The stability here derivates from the strain inside the crystal. Strains induced from MA and FA, which have different sizes, have different directions. And they make the crystal stable and count for the gentle red shift of temperature dependent photoluminescence spectra.Above results are paramount for the understanding of optical properties and structural phase transitions of perovskites. And they are meaningful for improving the phase stability and performance of perovskite optoelectronic devices.

钙钛矿 混合阳离子 光学性质 稳定性 应力

perovskite mixed cations optical properties stability strain

中文

联合培养

南方科技大学

庞国涛. MAxFA1-xPbI3 型钙钛矿材料的光学性质及结构相变研究[D]. 深圳. 哈尔滨工业大学,2019.