Flexible Lead Halide Perovskite Materials: Preparation And Properties

During the past decade,lead halide perovskites（LHPs）have emerged as popular semiconductor materials due to their outstanding photoelectronic properties.With the great promise of flexible electronics technology in the fields of wearable devices,bio–electronic interfaces,and intelligent manufacturing,LHP flexible electronics is also developing.As LHP crystals are essentially rigid,the development of LHP materials with flexibility is crucial to the flexible electronic applications.At present,LHPs can be made flexible primarily through two methods:the first is to optimize their intrinsic nanostructure,e.g.by making them into ultrathin nanosheets or ultrafine nanowires;the second is to fabricate composites based on flexible matrixes,including soft polymers and organogels.The former has not yet realized macroscopical flexibility,whereas the latter has reached this goal but the insulating matrixes render the composite non-semiconducting and mostly inaccessible for electrical applications.Here,we are committed to improving and innovating on the construction strategies of flexible LHP materials.Firstly,by optimizing the thickness of LHPs to the unit-cell level,the flexibility of inorganic frameworks was greatly exerted.Then,oligomers consisting of flexible molecular chains were introduced into the A-site of LHPs,which induces a transition from crystalline to amorphous and leads to mechanical flexibility.Further,this amorphous LHP was employed as the matrix for the construction of composites with conventional crystalline LHPs,thus extending the flexibility to common LHP materials.As the composites consist entirely of LHPs,they maintain the semiconducting properties of LHPs while ensuring flexibility,which are superior to conventional LHP composite materials that literally lose semiconductivity.In the second chapter,the flexibility of LHPs was enhanced by reducing the thickness of inorganic frameworks.CsPbBr3 perovskite was prepared with the assistance of protonated oleylamine,which strongly bonds to the（001）plane and facilitates two-dimensional growth.Besides,three-dimensional kinetics was suppressed by reducing the Cs reactivity.Finally,flexible CsPbBr3 nanoribbons with only two-unit-cell thickness and micron-sized lateral dimension were obtained,which exhibit blue-violet emission peaked at 435 nm due to the strong quantum confinement.The nanoribbons have a modulus of 320 MPa,which is about one-fiftieth that of typical CsPbBr3 crystals,giving full play to the flexibility of inorganic frameworks brought by the ultra-thin thickness.In the third chapter,the A-site organic components of LHPs were optimized.Jeffamine D230 with a flexible polyether molecular chain was utilized as the A-site species.Jeffamine molecules are not crystallizable in nature,which prevents them from packing crystalline when integrated into the A-site of LHPs and causes the entire LHP to become amorphous.Microscopically,the product exhibits an ultrathin and highly flexible lamellar nanostructure.Macroscopically,it resembles a liquid polymer,which exhibits liquid fluidity with a storage/loss modulus of 0.495 k Pa/75.8 k Pa（under 10rad/s）.It exhibits pseudoplastic shear-thinning with a viscosity 10⁴ times that of the original oligomer,and undergoes a glass transition at low temperatures.Besides,it possesses optical properties typical of low-dimensional LHPs.The special fluidity endows the amorphous LHPs with macroscopic flexibility.In the fourth chapter,in order to demonstrate the macroscopic flexibility in common LHPs,the aforementioned amorphous LHPs were composited with crystalline CsPbBr3 perovskites.By mixing D400 and Cs as the precursors for the A-site,a crystalline–amorphous composite of LHP was produced in situ,which combines liquid-polymer fluidity and halide-perovskite semiconductivity.We demonstrated that the crystalline and the amorphous parts were electronically coupled,which allows electronic wave functions to distribute throughout the composite and leads to semiconducting properties comparable to bulk LHP crystals.The composite exhibits electrical conductivity of the order of 10^-5 S/m with thermosensitive behavior that is characteristic of semiconductors.Moreover,the composite exhibits UV and X-ray photoelectric response properties,with a responsivity/sensitivity of 0.41 m A/W and0.399μC·Gyair^-1·cm^-2,respectively,which lays the foundation for related flexible applications.The in-situ compositing strategy is also applicable to LHPs with various halogen compositions and similarly yields a fluidic product,thus transforming LHPs into soft semiconductors with unprecedented fluidity.