Experimental and theoretical study of europium-doped organometal halide perovskite nanoplatelets for UV photodetection with high responsivity and fast response

Herein, we investigate the role of Eu³⁺ doping on CH₃NH₃PbBr₃ nanoplatelets (NPLs) in terms of their optoelectronic properties and photodetection application through a combined experimental and theoretical approach. The introduction of EuCl₃ in the CH₃NH₃PbBr₃ crystal structure by a facile solvothermal method enabled the tuning of the lateral and vertical dimensions of the NSs to form large-area NPLs and finally monolayer nanocrystals. The appearance of low-angle diffraction peaks with Eu doping, which are observed in layered perovskite structures, confirms the formation of quasi-2D NPLs. The bandgap of the Eu-doped mixed halide perovskite systematically increases from 2.39 eV to 2.94 eV with increasing doping concentration. Interestingly, 10 mol% EuCl₃ doping in the pure CH₃NH₃PbBr₃ crystal dramatically enhances its absorbance and photosensitivity, resulting in high-performance photodetection. Under 405 nm excitation, the CH₃NH₃Pb_0.9Eu_0.1Br_2.7Cl_0.3 photodetector exhibits self-biased behavior with an on/off ratio >10³, which is very significant. The planar device achieves a responsivity as high as 5.29 A W^- and a detectivity of 1.06 × 10¹² Jones under 405 nm with a power density of 0.14 mW cm^-2 at 5 V. In addition, the device exhibits very fast response time with a rise/fall time of 17.5/38.5 μs, which is ∼4 times faster than the pristine CH₃NH₃PbBr₃ counterpart. A linear relationship of photocurrent with light intensity in the CH₃NH₃Pb_0.9Eu_0.1Br_2.7Cl_0.3 photodetector signifies low recombination or charge trapping loss. High-performance photodetection in the Eu-doped device is ascribed to the elimination of trap states and the fast charge transfer process. To obtain better insight into the doped system, DFT analysis of the electronic structure of EuCl₃-doped CH₃NH₃PbBr₃ was performed and the results are fully consistent with the experimental findings. It was revealed that EuCl₃ doping increases the density of states near the conduction band along with a blue shift in the bandgap as compared to that of the pristine perovskite, which in turn increases the built-in potential of the fabricated device, resulting in self-biased photodetection. This work paves the way for deeper understanding of lanthanide doping in perovskites and self-biased photodetection applications of a new family of Eu-doped mixed halide perovskite nanostructures.