A-Site Cation Engineering of Ruddlesden–Popper Perovskites for Stable, Sensitive, and Portable Direct Conversion X-ray Imaging Detectors

Abstract

Perovskite flat-panel X-ray detectors are promising products for realizing low-dose medical imaging, a nondestructive test, and security inspection. However, the perovskite X-ray imager still faces intractable problems such as severe baseline drift, a low signal-to-noise ratio, and rapid performance degradation, which were involved by the notorious intrinsic ion migration of the perovskite functional layer. In this work, sensitive, stable, and portable pixel quasi-two-dimensional (2D) Ruddlesden–Popper (RP) perovskite X-ray imagers were obtained by an advanced solvent-free laminated fabrication approach. A-Site cation engineering of RP perovskites provides a hint for solving the trade-off between stability and detection performance, resulting in a stable pixel X-ray imager that shows a sensitivity of ∼7000 μC Gyair –1 cm–2, a detection limit of 7.8 nGyair s–1, and good 2D multipixel X-ray imaging. This work demonstrates both a high-performance, stable X-ray imager and its robust fabrication, paving the way for adopting a RP perovskite imager as novel flat-panel X-ray detectors.

Halide perovskites for sensitive, stable and scalable X-ray detection and imaging

“…Reproduced with permission. 97 Copyright 2022, American Chemical Society. (e) Photograph (left) and X-ray image (right) of a standard Pb phantom acquired by the MAPb(I 0.9 Cl 0.1 ) 3 detector.…”

“…Reproduced with permission. 97 Copyright 2022, American Chemical Society. (h) X-ray imaging of the BA 2 MA 9 Pb 10 I 31 X-ray detector.…”

Research Progress on Low-dimensional Halide Perovskite Direct X-ray Detectors

“…MA3Bi2I9 单晶具有优异的探测性能，为进一步 实现该材料的应用，2020 年，Tie 等 [77] 采用等静压 制备工艺，将 MA3Bi2I9 晶体粉末压制成型，制备了 毫米级厚度的 MA3Bi2I9 多晶片。该 多晶 片 具有 6 Quasi-2D polycrystalline X-ray detector (a) Preparing of RP perovskite -nylon matrix by a lamination process [26] ; (b) Photograph and corresponding X-ray image of a copper Chinese characters pattern [26] ; (c) A-site cation engineering to prepare RP perovskite X-ray detectors [22] ; (d) Microstructure of the TFT substrate and 12×12 pixel perovskite X-ray detector [22] ; (e) Images of visible light and X-rays based on BA2MA9Pb10I31 detector [22] ; (f) X-ray image based on (BA2PbBr4)0.5-FAPbI3 device [83] ; (g) Dark current uniformity of MAPbI3 device (left) and quasi-2D PEA2MA8Pb9I28 device (right) [84] 子的尺寸对离子迁移及电子传输存在直接影响。阳 [85] 。同时，利用 钙钛矿材料的铁电性质也可以达到类似的效果，值 得探索。电极结构设计对器件性能影响显著。通过 设计具有暗电流分流作用的电极结构，可以有效降 低 X 射线探测器的暗电流，同时减少噪声和基线漂 移 [86] 。通过设计更先进的器件结构实现高性能探测 器，是值得研究的重要方向。 (3)…”

“…国亟待攻克的"卡脖子"技术之一。因此，研发先进 的探测材料及技术为打破探测器领域自身的技术限 制及国外技术封锁均具有十分重要的意义。 X 射线探测器分为直接型和间接型两种。 相比 于间接型，直接型探测器的像素串扰问题较少，理 论空间分辨率更高 [4] 。 非晶硒 (a-Se) [5] ， 碲锌镉 (CZT) [6] 等是直接型 X 射线探测器的典型代表。目前，a-Se 与薄膜晶体管(TFT)阵列结合，实现了大面积 二维 X 射线成像。 然而， a-Se 对射线的吸收能力差， 载流子迁移率低， 以及易晶化导致了工作不稳定性， 极大地限制了其应用范围。CZT 的基本性质十分契 合 X 射线探测的需求，然而大尺寸、高质量的 CZT 制备困难， 只有少数几个国家和地区掌握相关技术。 CZT 单晶的高温(>1000 ℃)制备工艺限制了其在 商业 TFT 基板直接沉积的可能性。其他常见的直接 型 X 射线探测材料：硅 [7] 、锗 [8] 、碘化汞 [9] 等存在 X 射线吸收能力和稳定性差等问题，应用也受到极大 限制。 近年来，卤化物钙钛矿由于光电性质优异、带 隙可调、制备简单、成本低等优点，在材料科学、 光电子领域引起了广泛关注 [10] 。钙钛矿的高原子序 数 (Z) 和高载流子迁移率使其适用于 X 射线检测。 与传统的 a-Se、CZT 相比，钙钛矿材料的主要优势 如下： (1)缺陷容忍度高，载流子迁移率高和载流 子寿命长。 (2)组分和结构可调，为材料性质调变 提供了丰富的操作平台。 (3)制备方法简单多样， 包括刮刀涂布 [11] 、旋涂 [12] 、喷涂 [13] 、热压 [14] 、模板 辅助生长法 [15] 以及数字喷墨打印 [16] 等。 根据八面体结构基元在不同方向上的连接方式， 钙钛矿被分为三维(3D) 、2D、1D 和 0D 结构 [17] 。 自 2015 年 Yakunin 等首次报道了基于 3D MAPbI3 多晶膜 X 射线探测器之后， 钙钛矿 X 射线探测器取 得了引人瞩目的进展，灵敏度>10 4 µC • Gyair −1 • cm −2 ， 远优于商业化 a-Se 探测器 [18][19][20][21] 。然而，由于 3D 钙 钛矿存在较严重的离子迁移，导致噪声大和基线漂 移严重等问题，不利于获取低检测下限及高稳定性 器件 [22] 。2021 年，Liu 等 [23] 发现具有复合 A 位阳离 子的三维钙钛矿单晶可以在一定程度上抑制离子迁 移。如何进一步抑制钙钛矿离子迁移是获得具有高 稳定性 X 射线探测器的关键。 研究发现， 低维 (2D、 1D、0D)钙钛矿材料在微观结构上可以隔断离子迁 移 通 道 ， 进而更好地 抑制离 子 迁 移 [24] 。 例如， MA3Bi2I9、Cs3Bi2I9、(NH4)3Bi2I9、Ruddlesden-Popper (RP)钙钛矿等低维材料的离子迁移激活能(Ea) 较大 [24][25][26][27][28][29]…”

Low-Dose and Stable X-ray Detection Enabled by Ferroelectric Perovskite Oxides

“…X-ray imaging has become increasingly prominent as the auxiliary evidence for the chest diagnosis and treatment. However, frequent radiation often increases the risk of cancer in the human body. − To increase the frequency and fidelity of diagnostic technologies for early diagnosis of diseases without sacrificing imaging quality, high-performance X-ray detectors for low-dose detection are urgently needed. − Direct X-ray detection has obvious advantages over the indirect ones in resolution and simpler system configuration. − For direct X-ray detection, electron–hole pairs (EHPs) are generated in the photoconductive layer after absorbing incident X-ray photons and are collected by the electrodes in opposite direction under external bias. , Therefore, the efficiency of carrier separation and extraction in the photoconductive layer influences the performance of direct X-ray detectors. Though high bias voltages can provide a large driving force to ensure a sufficient separation of EHPs, large dark current is introduced as well, which is an unpleasant source of noise. , Noise is a random component added to the image signal, existing as white dots appearing randomly in the image.…”