The Preparation And Optoelectronic Performance Of Perovskite Halide Materials

Due to their many excellent advantages,such as direct and tunable bandgap,long carrier lifetime,high defect tolerance,and excellent charge-carrier mobilities,halide perovskite materials have been gaining considerable attentions for applications in solar cells(PSCs),light emitting diodes(PeLEDs)and other fields.In the field of PSCs,metal electrode atoms will diffuse through carrier transport layers(CTLs)into the perovskite film,distorting the film structure and reducing device stability in the planar structure perovskite photoelectronic devices.In the field of PeLEDs,inorganic halides are difficulty to be completely dissolved in organic solvents,increasing the difficulty of device fabrication.Meanwhile,the external quantum efficiency(EQE)of flexible PeLED needs to be further improved.To resolve the above problems,this paper starts from the materials fabrication process and device structure optimization to improve the performance of perovskite photoelectric devices.The main contents of this paper are divided into the following three sides:(1).We innovatively use an ultra-thin layer of titanium(Ti)to replace organic electron transport layers to fabricate efficient PSCs device in inverted planar structure.X-ray photoelectron spectroscopy(XPS)and soft X-ray absorption near edge structure(XANES)results prove that a Ti-N bonding layer was formed between Ti atoms and nitrogen(N)atoms in metylammonium(MA+)anions at perovskite/Ti interface.The bonding layer fixed the MA+ and maintained the stability of perovskite interface.Meanwhile,the low-diffusivity Ti film serves as a compact blocking layer to prevent the diffusion of metal atoms into the perovskite layer.The photovoltaic performance measurements show that the champion PSCs device with 10 nm titanium as the electron transport layer has the highest photoelectric conversion efficiency(PCE)of 18.1%.(2).The green PeLED device was fabricated by the thermal evaporation.By controlling the deposition rate of MABr,the post-annealing temperature and substrate temperature,the MAPbBr3 film with the optimal composition was obtained.The fabricated MAPbBr3 green PeLED device has the electroluminescence peak(EL)at 520 nm and the max external quantum efficiency(EQEMAX)of 1.6%.And the EQEMAX was improved to 3%by spin-coating thin MAPbBr3 film on the substrate to assist the dual source co-evaporation process.The green LED device based on CsPbBr3-Cs4PbBr6 heterojunction light emitting layer was prepared by the dual-source co-evaporation.The coexistence structure of Cs4PbBr6 phase and CsPbBr3 phase was fabricated by adjusting the evaporation and post-annealing process.Thus,the prepared CsPbBr3-Cs4PbBr6 heterojunction green LED device has the EL at 518 nm and the EQEMAX of 2.3%.And the EQEMAX was further improved to 3.2%after the FPMABr film was spin-coated on the heterojunction film to passivate these surface dangling bonds.(3).Efficient flexible near-infrared PeLED devices were fabricated by the spin coating process.By calculating the tolerance factor,the composition of the perovskite light-emitting layer was fixed as FA0.83Cs0.17Pb(I0.9Br0.1)3.By optimizing the thickness of the FET conductive layer and the molar ratio of the longer-chain organic cation,the EQEMAX of the PET and PEN substrate PeLED devices were 14.4%and 15.1%,respectively.Based on optical analysis,these reasons for the increased light extraction efficiency of the PET and PEN substrate devices may be the higher haze and more matched refractive index of the substrates,compared with traditional ITO substrate.Fatigue testing showed that the performances of these flexible PeLED devices were maintained even after bending for 2,000 cycles at a radius of 2 mm.