Near-infrared light-emitting diodes (NIR-LEDs) are widely used in various applications such as night-vision devices, optical communication, biological imaging and optical diagnosis. The current solution-processed high-efficiency perovskite NIR-LEDs are typically based on CsPbI3 and FAPbI3 with emission peaks being limited in the range of 700–800 nm. NIR-LEDs with longer emission wavelengths near to 900 nm can be prepared by replacing Pb with Sn. However, Sn-based perovskite LEDs usually exhibit a low efficiency owing to the high concentration of Sn-related defects and the rapid oxidation of Sn2+ to Sn4+, which further induces the device degradation. These problems can be solved by rationally adjusting the ratio between Pb content with Sn. Mixed Sn-Pb halide perovskites with a smaller bandgap and superior stability than pure Sn-based perovskites are promising candidates for manufacturing next-generation NIR emitters. In this study, we systematically investigated the optical properties of a family of hybrid Sn and Pb iodide compounds. The emission spectra of the mixed Sn-Pb halide perovskites were tuned by changing the Sn:Pb ratio. Consequently, the peak emission wavelength red-shifted from 710 nm to longer than 950 nm. The absorption and photoluminescence emission properties associated with different compositions were compared, and the results demonstrated the potential of MA- and FA-based mixed Sn-Pb halide perovskites for preparing low-cost and efficient NIR-LEDs. In addition, we clarified the influence of cations on the bandgap bowing effect and electronic properties of mixed Sn-Pb halide perovskites.

Tin–lead perovskite-based photodetectors have a wide light-absorption wavelength range, which spans 1000 nm. However, the preparation of the mixed tin-lead perovskite films faces two great obstacles, namely easy oxidation of Sn2+ to Sn4+ and fast crystallization from tin-lead perovskite precursor solutions, thus further resulting in poor morphology and high density of defects in tin-lead perovskite films. In this study, we demonstrated a high-performance of near-infrared photodetectors prepared from a stable low-bandgap (MAPbI3)0.5(FASnI3)0.5 film modified with 2-fluorophenethylammonium iodide (2-F-PEAI). The addition engineering can efficiently improve the crystallization of (MAPbI3)0.5(FASnI3)0.5 films through the coordination binding between Pb2+ and N atom in 2-F-PEAI, and resulting in a uniform and dense (MAPbI3)0.5(FASnI3)0.5 film. Moreover, 2-F-PEAI suppressed Sn2+ oxidation and effectively passivated defects in the (MAPbI3)0.5(FASnI3)0.5 film, thereby significantly reducing the dark current in the PDs. Consequently, the near-infrared photodetectors showed a high responsivity with a specific detectivity of over 1012 Jones at 800 to near-1000 nm. Additionally, the stability of PDs incorporated with 2-F-PEAI has been significantly improved under air conditions, and the device with the 2-F-PEAI ratio of 400:1 retained 80% of its initial efficiency after 450 h storage in air without encapsulation. Finally, 5 × 5 cm2 photodetector arrays were fabricated to demonstrate the potential utility of the Sn–Pb perovskite photodetector in optical imaging and optoelectronic applications.

Here, we present a new two-electrode photo-rechargeable FTO/TiO2/Cs3Bi2I9/Pt/FTO system. The key material is the photoactive lead-free perovskite Cs3Bi2I9 which performs photoelectric conversion and provides energy storage. This study is the...