Low Trap Density Para-F Substituted 2D PEAPbX (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 PEAPbX (X = Cl, Br, I) and their para-F (-F) substitution analogs are prepared using the facile solution method to study the effects of both -F substitution and halogen anion engineering. After -F substitution, the triclinic PEAPbX (X = Cl, Br) and cubic PEAPbX (X = I) crystals unifies to monoclinic crystal structure for -F-PEAPbX (X = Cl, Br, I) crystals. The -F substitution and halogen engineering, together with crystal structure variation, enable the tunability of optoelectrical properties. Experimentally, after the -F substitution, the energy levels are lowered with increased Fermi levels, and the bandgaps of -F-PEAPbX (X = Cl, Br, I) are slightly reduced. Benefitting from the enhancement of the charge transfer and the reduced trap density by -F substitution and halogen anion engineering, the average carrier lifetime of the -F-PEAPbX is obviously reduced. Compared with PEAPbI, the X-ray detector based on -F-PEAPbI perovskite single-crystal has a higher sensitivity of 119.79 C Gy ·cm. Moreover, the X-ray detector based on -F-PEAPbI single crystals exhibits higher radiation stability under high-dose X-ray irradiation, implying long-term operando stability.