Low Trap Density Para-F Substituted 2D PEA2PbX4 (X = Cl, Br, I) Single Crystals with Tunable Optoelectrical Properties and High Sensitive X-Ray Detector Performance

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 PEA2PbX4 (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 PEA2PbX4 (X = Cl, Br) and cubic PEA2PbX4 (X = I) crystals unifies to monoclinic crystal structure for p-F-PEA2PbX4 (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-PEA2PbX4 (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-PEA2PbX4 is obviously reduced. Compared with PEA2PbI4, the X-ray detector based on p-F-PEA2PbI4 perovskite single-crystal has a higher sensitivity of 119.79 μC Gyair-1·cm-2. Moreover, the X-ray detector based on p-F-PEA2PbI4 single crystals exhibits higher radiation stability under high-dose X-ray irradiation, implying long-term operando stability.