Research On The Controllable Preparation Of Cesium Copper Halides And Theirs Applications In Light-emitting Devices

In the past few years,metal lead halide perovskite has become one of the most promising potential photoelectric materials.Due to its adjustable band gap,high absorption coefficient,low exciton binding energy,and high carrier mobility,many excellent results have been achieved in the research on metal lead halide perovskites in recent years.Especially the excellent properties of lead metal halide perovskite in luminescence,the external quantum efficiency(EQE)of lead metal halide perovskite LED has rapidly increased from 0.1%to more than 20%.It demonstrates the great potential of metal lead halide perovskite in the next generation of display applications.However,lead metal halide perovskites are very sensitive to moisture,oxygen,heat,and ultraviolet rays in the air,they are easily decomposed,and their luminescence performance will be severely degraded.Secondly,the metal lead halide perovskite contains the heavy metal element lead(Pb),which is potentially dangerous to the environment.Therefore,looking for stable lead-free materials with excellent luminescence properties is more in line with future development needs.In this study,cesium copper halides Cs₃Cu₂I₅ and Cs Cu₂I₃are selected as research objects.First,use the supersaturated recrystallization method to grow Cs₃Cu₂I₅ and Cs Cu₂I₃ micron crystals,and successfully combine them with white light-emitting diode(WLED)devices.After that,Cs₃Cu₂I₅ nanocrystals were grown by high-temperature thermal injection,and a deep blue LED based on Cs₃Cu₂I₅ nanocrystals was successfully realized.The following main conclusions are obtained:1.The Cs₃Cu₂I₅ and Cs Cu₂I₃ micro-crystals were synthesized by a simple supersaturated recrystallization method at room temperature,and stable and efficient WLEDs were successfully prepared by using blue Cs₃Cu₂I₅ and yellow Cs Cu₂I₃ as down-conversion phosphors.Their broadband emission characteristics enable their combined spectrum to cover the entire visible light region,and they benefit from the large Stokes shift caused by the STEs-related recombination mechanism,which effectively avoids the problems of undesired photon self-absorption and color instability.The performance of the WLED is excellent,with a CRI of 88.4 and high luminous efficiency(LE)of 54.6 lm/W.The unpackaged WLED can effectively maintain 100 hours in the continuous current mode without any emission attenuation,which shows excellent long-term working stability.2.Successfully synthesized OD Cs₃Cu₂I₅ nanocrystals at 160°C by using an improved thermal injection method.Under normal circumstances,the synthesized Cs₃Cu₂I₅ nanocrystals show a strong blue emission with a PLQY of 87%.The optical characteristics verify that the broadband blue emission of Cs₃Cu₂I₅ with a large Stokes shift is caused by STEs.The first calculation result of the principle of sex also proves this point.In addition,experiments and theory prove that this Cs₃Cu₂I₅ nanocrystal has significant stability to heat and ambient oxygen/moisture.By using blue-emitting Cs₃Cu₂I₅ nanocrystals as the light-emitting body,a multilayer heterojunction Al/Li F/TPBi/Cs₃Cu₂I₅/Ni O/ITO was designed to successfully fabricate an electrically-driven deep blue LED and achieve a high EQE of about 1.12%.More importantly,the blue LED showed excellent working stability in continuous current mode,producing a record T₅₀ of about 108 hours.In addition,an aggressive thermal cycle test(300-360-300 K)and a 35-day storage test were also carried out to further demonstrate the stability and repeatability of the proposed device.