Low Trap Density Para-F Substituted 2D PEA <sub>2</sub> PbX <sub>4</sub> (X = Cl, Br, I) Single Crystals with Tunable Optoelectrical Properties and High Sensitive X-Ray Detector Performance
Jiayu Di, Haojin Li, Li Chen, Siyu Zhang, Yinhui Hu, Kai Sun, Bo Peng, Jie Su, Xue Zhao, Yuqi Fan, Zhenhua Lin, Yue Hao, Peng Gao, Kui Zhao, Jingjing Chang
Abstract
Exploring halogen engineering is of great significance for reducing the density of defect states in crystals of organic-inorganic hybrid perovskites and hence improving the crystal quality. Herein, high-quality single crystals of PEA 2 PbX 4 (X = Cl, Br, I) and their para-F ( p -F) substitution analogs are prepared using the facile solution method to study the effects of both p -F substitution and halogen anion engineering. After p -F substitution, the triclinic PEA 2 PbX 4 (X = Cl, Br) and cubic PEA 2 PbX 4 (X = I) crystals unifies to monoclinic crystal structure for p -F-PEA 2 PbX 4 (X = Cl, Br, I) crystals. The p -F substitution and halogen engineering, together with crystal structure variation, enable the tunability of optoelectrical properties. Experimentally, after the p -F substitution, the energy levels are lowered with increased Fermi levels, and the bandgaps of p -F-PEA 2 PbX 4 (X = Cl, Br, I) are slightly reduced. Benefitting from the enhancement of the charge transfer and the reduced trap density by p -F substitution and halogen anion engineering, the average carrier lifetime of the p -F-PEA 2 PbX 4 is obviously reduced. Compared with PEA 2 PbI 4 , the X-ray detector based on p -F-PEA 2 PbI 4 perovskite single-crystal has a higher sensitivity of 119.79 μ C Gy air -1 ·cm -2 . Moreover, the X-ray detector based on p -F-PEA 2 PbI 4 single crystals exhibits higher radiation stability under high-dose X-ray irradiation, implying long-term operando stability.