| Due to adjustable band gap,simple preparation process,low cost and good photoelectric properties,perovskite materials has been considered as a promising new photoelectric material in recent years.Among them,organic-inorganic hybrid perovskite materials own excellent photoelectric properties.The photoelectric conversion efficiency of solar cells based on organic-inorganic hybrid perovskite has been increased from 3.8%to 25.73%in just about ten years.However,the organic components in organic-inorganic hybrid perovskite are volatile and the water stability is poor,which affects the lifetime of devices.Compared with organic-inorganic hybrid perovskite materials,all-inorganic perovskite materials have better thermal stability,so they are more hopeful of commercialization.All-inorganic perovskite materials also have higher carrier mobility and longer carrier lifetime,and the related research has become more and more popular.The photoelectric conversion efficiency of the solar cell based on CsPbI3 all-inorganic perovskite has reached 20%,and the External Quantum Efficiency(EQE)for the green Light Emitting Diodes(LED)based on CsPbBr3 has reached 28.9%.All-inorganic perovskite films are ideal materials for photodetectors,and their stability can improve the durability of photodetectors in military,environmental detection,medical and aerospace fields.However,the poor film quality of all-inorganic perovskites with high trap density and crystals defects leads to the nonradiative charge recombination,bringing about poor performance of devices.A number of strategies have been carried out to improve their film quality,such as the use of organic additives,passivators,quantum dots,and ions doping etc,resulting in the enhanced performance of these devices.However,the improvement of film quality by the above methods is limited,and the residual components will also reduce the stability of the device.Lanthanide rare earth ions,due to their unique optical properties and rich 4fn/4fn-1 5d energy levels,are usually used as sensitizers in luminescent materials to improve the photoluminescence efficiency of films through quantum tailoring effect.Lanthanide(Ln3+)ions have a similar ionic radius of lead(Pb2+),which are recognized as an ideal doping candidate to substitute Pb2+.So far,europium ions(Eu3+),ytterbium ions(Yb3+),cerium ions(Ce3+),samarium ions(Sm3+)and Erbium ions(Er3+),have been doped into perovskite nanocrystals(CsPbI3)to significantly boost the optical performance,Ce3+,Nd3+and Er3+ have been proved to improve the crystallinity of hybrid perovskite materials.However,there is few reports for lanthanide rare-earth ion doped perovskite films systematically.Based on the above problems,we have made the following research:(1)We compared with CsPbI3 film and CsPbI2Br film,and proved that the introduction of Br improved the tolerance factor and thus improved the stability of the film.Then,we optimized the preparation process of the films.Pretreating PbI2 and PbBr2 by DMSO could reduce the holes and improve the film quality.The improved film roughness was reduced to 1.38 nm.At the same time,the film exhibited more excellent conductivity and stability under daily conditions.(2)Various lanthanide rare earth ions Pr3+,Gd3+,Nd3+,Eu3+,Tm3+,Ho3+ and Yb3+were doped into CsPbI2Br films.The results showed that the grain size increased from～110 nm to～400 nm,and the films showed better quality and fewer holes.The doped films owned better light absorption ability at the wavelength range of 300-700nm,and the conductivity was increased to 7.81 × 10-4 S cm-1,electron and hole defect density is decreased to 4.059 × 1016 cm-3 and 7.74 × 1016 cm-3.The most important,the stability of the films in the air was also greatly improved.At the range of 400-600 nm wavelength,the photodetectors base on CsPbI2Br:Ln3+films exhibited better detectivity.(3)Because Yb3+doped films exhibit the best photoelectric properties,we changed the doping concentration and found the best doping ratio of 2%.According to XPS and Williamson-Hall calculation method,the real reason that Yb3+improves the film quality and stability is that the cyclic redox reaction of Yb3+-Yb2+pair reduces the Pb and I defects,and the introduction of Yb3+reduces the lattice strain,thus improving the films’ stability.Based on the above research,we prepared photodetectors by 2%Yb3+doped CsPbI2Br film,which also showed excellent photoelectric detection performance:the photodetectors achieved effective photoelectric response at the range of 300-700 nm,and the detectors’ detectivity(D*)reached 4.6 × 1012 Jones,the fastest response time is 680 ns.And the stability of the photodetectors was also greatly improved,after 15 days in the air,the performance still remained 90%of original. |
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