Fund Project:Project supported by the National Natural Science Foundation of China (Grant No. 11805180)
Received Date:08 April 2021
Accepted Date:17 May 2021
Available Online:07 June 2021
Published Online:05 October 2021
Abstract:As a novel low-cost semiconductor with extraordinary photoelectric property, the inorganic CsPbX3 perovskites have become emerging materials for the next generation of X-ray detectors in the past decade. However, most of recent studies of CsPbX3 perovskite X-ray detectors are based on their internal photoelectric effect. Though it is also important and widely used in vacuum X-ray detectors, the external photoelectric effect of CsPbX3 perovskite has been rarely studied by now. Thus, the response sensitivity of the CsPbX3 perovskite’s external photoelectric effect in the X-ray region is studied in the present paper. First, a 230-nm-thick CsPbI2Br membrane is prepared on a metal substrate by a conventional one-step deposition method, with a precursor solution used. Then the external photoelectric responsivity and quantum efficiency of the CsPbI2Br membrane are calibrated in a range from 2000 to 5500 eV at Beijing Synchrotron Radiation Facility. The responsivity is over 5.1 × 10–5 A/W in the range and the quantum efficiency is over 23%. These calibration data are close to those of a traditional X-ray photoelectric material CsI. The Monte-Carlo method is utilized to simulate the external photoelectric effect of CsPbI2Br perovskite, and the external photoelectric responsivity is calculated. The calculated data match well with the calibration, proving the Monte-Carlo method feasible for the external photoelectric effect simulation of CsPbX3 perovskite. Then the external photoelectric responsivities and quantum efficiencies of CsPbX3 perovskites are calculated via the Monte-Carlo method in the X-ray range from 2000 to 10000 eV. The calculated responsivities of different CsPbX3 perovskites are all close to the responsivity of CsI, and an order of magnitude higher than that of Au, and the CsPbX3 quantum efficiencies also follow a similar scenario. This indicates that CsPbX3 perovskites have good external photoelectric properties and potential applications in X-ray vacuum detectors such as photocathode and photomultiplier. The influence of thickness on CsPbX3 photoelectric response is also studied in this paper via Monte-Carlo simulation. The results show that the responsivity increases with the material thickness increasing, which is due to the increased X-ray absorption. The responsivities all reach their upper limits at a material thickness of about 150 nm, which means that the electrons generated at 150 nm can hardly escape from the material surface. It is indicated that the thickness of CsPbX3 should be no less than 150 nm to obtain the optimal photoelectric response. Keywords:CsPbX3/ X-ray/ external photoelectric effect/ responsivity
全文HTML
--> --> --> -->
2.1.CsPbI2Br的制备与表征
不同CsPbX3钙钛矿材料的晶体均为Pm-3m立方结构, 其区别主要在于不同的卤素原子及配比导致的晶胞大小不同, 因此不同CsPbX3钙钛矿材料的能带结构也十分相似, 其光电特性也具有一定的相似性[11-13]. 不同CsPbX3钙钛矿材料可以通过改变卤族元素的比例配制出相应的前驱液, 然后通过旋涂或者刀刮前驱液的工艺制备成薄膜, 最后进行退火获得相应钙钛矿材料[13-15]. 而其中的CsPbI2Br为混合阴离子结构, 其晶体结构与能带参数介于CsPbI3和CsPbBr3之间. 同时CsPbI2Br在大气环境下存放超过800 h仍能保持相应的结构和光电特性[15-17], 具有很好的化学稳定性和热稳定性, 其在X光波段的吸收系数也高于GaAs, Si等传统半导体材料. 因此, 本文选择CsPbI2Br作为制备和测试CsPbX3外光电效应的对象. 采用一次旋涂前驱液后退火的工艺[14]制备CsPbI2Br薄膜样品. 将0.1 mmol CsBr和0.1 mmol PbI2溶解在1 mL的二甲基亚砜(DMSO)中, 在70 ℃下搅拌4 h, 再使用0.22 μm的针孔过滤器进行过滤, 获得澄清的黄色前驱液; 将前驱液以1500 r/min的转速旋涂在金属片基底上, 然后160 ℃退火10 min, 最终获得了如图2(a)所示的棕红色CsPbI2Br薄膜样品. 该薄膜样品的X射线衍射(X-ray diffraction, XRD)数据和扫描电镜图像见图2(b). 样品XRD谱图在14.42°, 20.46°和29.30°有三个衍射峰, 分别对应CsPbI2Br的(100), (110)和(200)晶面. 从扫描电子显微镜照片可以看出, CsPbI2Br薄膜表面比较平整, 由直径百纳米左右的晶粒构成, 晶粒分布较为均匀, 薄膜表面有少量针孔, 但不影响整体的完整性. 通过Bruker Dektak XT台阶仪测得样品薄膜的厚度为230 nm. 图 2 (a) CsPbI2Br薄膜样品照片以及响应灵敏度测试排布示意图; (b) CsPbI2Br薄膜X射线衍射分析数据及扫描电镜照片 Figure2. (a) Photo of a CsPbI2Br membrane sample and the layout of spectral responsivity calibration; (b) XRD data and SEM photo of CsPbI2Br membrane sample.