Surface Engineering of All-Inorganic Perovskite Quantum Dots with Quasi Core−Shell Technique for High-Performance Photodetectors

All-inorganic lead halide perovskites with good surface morphology show substantial prospect for optoelectronic devices. However, the anion exchange of coordinated alkylamine ligands (e.g., oleic acid and oleylamine) can detach ligands and induce more interface trap sites, subsequently to reduce device performance. In this paper, therefore, a simple solution-processed route is presented to synthesize quasi coreshell CsPbBr₃formamidinium iodide (FAI = CH(NH₂)₂I) colloidal quantum dots (CQDs), and then it is applied as the active layer for photodetectors by finely controlling the ligands exchange. The presence of FAI = CH(NH₂)₂I on CsPbBr₃ is confirmed by Fourier transform infrared spectroscopy. As a result, the photodetector ITO/ZnO (100 nm)/CsPbBr₃ (150 nm)/Au show an enhanced specific detectivity over 10¹³ Jones with a responsivity of 19 A W¹ under 3 mW cm² 405 nm illumination at 1.5 V. The experimental data show that the enhanced device performance is due to the improved crystallinity and less surface defects of CsPbBr₃ CQDs, as the result of less alkylamine ligands is detached during its FAI passivation, thus the charge carriers' mobility of the film is improved. Therefore, it provides a promising way for high-performance solution-processed all-inorganic CsPbBr₃ based optoelectronic devices.