Spectroscopic/Optoelectronic Properties And Applications Of Impurity-Doped All-inorganic Perovskite Quantum Dots

The past several years have witnessed the rapid development of all-inorganic perovskite nanomaterials in the fields of photovoltaic and optoelectronic devices,owing to their exceptional spectroscopic and optoelectronic properties.However,the poor stability of all-inorganic perovskite materials which are vulnerable to water,oxygen,light and heat,has restricted their practical applications for a long time.In order to fundamentally resolve this limitation,in this thesis,we have selected the common 3D all-inorganic CsPbX₃?X=Cl,Br,I?perovskite quantum dots?QDs?as the research system,and then optimized or modified them by a doping strategy without changing their excellent performances.In addition,we also applied this doping strategy to the 0D Cs₄PbBr₆ perovskite nanomaterials that haven't been well studied so far,with an attempt to develope new properties of these theoretically nonluminescent 0D perovskites.Therefore,a variety of divalent metal ions such as Mn²⁺and Sn²⁺were selected as the dopants in this thesis.Starting from the synthesis of impurity-doped all-inorganic perovskite nanomaterials,the effects on the spectroscopic and optoelectronic properties and stability of host crystals added by doped ions were systematically discussed through experiments and first-principle calculations,and applications of as-synthesized nanomaterials were also preliminarily explored.The specific research content and results are as follows:?1?We have proposed and theoretically proved a strategy to stabilize the crystal lattice of CsPbX₃ perovskite QDs through Mn²⁺ions substitution for the first time.By comparing the temperature-dependent photoluminence?PL?emission spectra and doing controlled experiments under ambient air conditions for CsPbX₃ perovskite QDs doped with different Mn²⁺contents,we find that the CsPbX₃ perovskite QDs with proper Mn²⁺doping content have better thermal and air stability.Further combining with the first-principles calculations we verify that the improved stability is attributed to the enhanced formation energy after the introduction of Mn²⁺.In addition,the Mn²⁺doping strategy can add new optical properties to CsPbCl₃perovskite QDs,and improve the PL emission intensity and quantum yields of CsPbX₃ perovskite QDs at appropriate doping concentration.The light-emitting diode?LED?devices fabricated by using the as-synthesized Mn²⁺-doped CsPbX₃ perovskite QDs as an active light emitting layer also show more superior performances.In conclusion,the Mn²⁺substitution strategy might open up a new avenue to improve the stability of CsPbX₃ perovskite QDs for the fabrication of efficient LED devices.?2?We have proposed an effective strategy to tailor the insulator bandgap?³.96eV?of Cs₄PbBr₆ nanocrystals?NCs?to the blue spectral region by changing the local coordination environment of the isolated[PbBr₆]^4-octahedra in the Cs₄PbBr₆ crystal through Sn cation doping for the first time.Benefitting from the unique Pb²⁺-poor and Sn²⁺-rich reaction environment,the Sn cation is successfully introduced into the Cs₄PbBr₆ NCs,forming coexisting point defects comprising substitutional Sn_Pb and interstitial Br_i,and the as-synthesized Cs₄PbBr₆:Sn perovskite NCs have an ultranarrow blue emission peak at⁴37 nm?full width at half maximum,¹2 nm?which is a big breakthrough for these theoretically nonluminescent Cs₄PbBr₆ NCs.By combining the experimental results with first-principles calculations,an unusual electronic dual bandgap structure,comprising the newly emerged semiconducting bandgap of².87 eV and the original insulator bandgap of³.96 eV,is found to be the underlying fundamental reason for the ultranarrow blue emission in the Cs₄PbBr₆:Sn perovskite NCs.These findings unambiguously enrich the optical behaviors of Cs₄PbBr₆ perovskite NCs,and pave a new way for tailoring the bandgap of materials with similar structure.