| Since organgic-inorganic perovskite was reported,ABX3 organic-inorganic hybrid perovskite(A=methylamine,formamidine,cesium;B=lead or tin;X=chlorine,bromine,iodine or mixed halogen)has been widely studied in the field of photoelectric conversion all over the world.However,the lead element in lead-based perovskite is toxic to the environment,while the Sn2+in tin perovskite is relatively unstable,so their commercial application progress is slow.In order to solve the essential shortcomings of lead and tin based perovskites,more and more low-toxic and stable non-lead perovskites have been studied,among which bismuth and antimony series are the most representative.Moreover,Bi3+ and Pb2+ have very similar ionic radius and the same nuclear electron structure,which is meaningful in research prospects.Therefore,bismuth-based perovskite is the main research object in this paper.Bismuth-based perovskite material has a very rich structure,suitable and adjustable band gap,high light absorption coefficient,environment friendly and stable,cheap and easy to prepare.All these advantages provide good congenital advantages for its application,such as the preparation of better performance of a light detector.However,the shortcomings and research difficulties of bismuth-based materials are also very obvious:1.There are many kinds of bismuth-based materials that have not been reported;The relationship between structure and properties of bismuth-based materials is not clear.Bismuth-based materials are not as widely used as lead-based materials in photoelectric field.Fourth,the reported materials tend to show low photoelectric conversion efficiency in the visible light region.Therefore,the preparation and characterization of new bismuth-based materials,or the study of the relationship between the structure and properties of new bismuth-based materials,or avoid the low efficiency interval to further expand the scope of photoelectric application of existing bismuth-based materials,or improve the strategy to improve the photoelectric performance of existing bismuth-based materials,have always been meaningful research topics.Our paper includes the following contents:In chapter one,the basic structure,design rules and the definition of charge dimension of non-lead organic-inorganic hybrid perovskites are briefly introduced.Then,the structure classification of non-lead perovskite is introduced,including zero-dimension,one-dimension,two-dimension and three-dimension.The structural characteristics of bismuth perovskite are introduced emphatically,and the close relationship between structure and properties is highlighted.The application of bismuth-based perovskite materials in photoelectric field was introduced,and the advantages and research significance of bismuth materials in photoelectric field were highlighted.Some problems and research directions of bismuth series materials are summarized in detail.Finally,this paper introduces the significance of the topic and research content.In Chapter two,we reported for the first time the preparation method and application of a 0D bismuth-based perovskite hydrazine bismuth iodine(HyBI)single crystal.The crystal structure,thermal stability,band gap,semiconductor properties and photoelectric properties were tested in detail.HyBI has a direct band gap of 1.99 eV,a mobility of 64.2 cm2 V-1s-1,and a charge trap density of 2.32×1010 cm-3.In addition,a self-driven photodetector with a response rate of 7.63 mA/W at 470 nm was fabricated using this material.This work highlights this material as a promising candidate for lead-free optoelectronic materials in a new generation of self-driven optoelectronic detecter.In chapter three,we prepared two 1D photoactive bismuth-based perovskites,p-phenylenediamine bismuth iodine(PDABI)and p-iodoaniline bismuth iodine(PIDBI),and discussed their single crystal structure,band gap,thermal stability,electrical,photoelectric response and other properties.They all have a one-dimensional BiI4-anion chain consisting of a common BiI6 octahedron.DFT results show that there is interaction between I substituents on organic cations and Bi atoms on inorganic chains in PIDBI.The photoelectric response of PDABI with symmetric cations is better than that of PIDBI.The experimental results show that the interaction between the symmetric cation and anion chain is beneficial to the photoelectric properties of bismuth-based materials compared with PIDBI.This conclusion has certain guiding significance for the design of other bismuth perovskite absorbent materials.In chapter four,we first compare the crystal structure,band gap,band structure,electrical and photoelectrical properties of benzylamine bismuth iodine(BABI)and N-methylaniline bismuth iodine(NMABI).They all have typical A3Bi2I9 0D structure,good thermal stability,similar band gap(BABI 2.00 eV,NMABI 2.04 eV),easy to spin coating film,film uniformity and good stability.The band structure calculated by DFT shows that C 2p orbital of BABI is closer to the band edge than that of NMABI.Compared with the Z-type π-π packing,the face-to-face Ⅰ-type π-π packing enhances the π-π conjugation between benzene rings,plays a key role in the electron transfer process,and improves the charge transfer dimension of materials.SCLC results show that compared with BABI,NMABI has lower resistivity,lower trap state density and higher carrier mobility,but BABI has better photoelectric performance according to the photocurrent response.This result further proves that the establishment of charge transfer dimension is more conducive to the improvement of photoelectric properties of materials.In addition,we also prepared a centimeter-sized BABI single crystal and applied it to UV detection.When the channel direction of the strip electrode is perpendicular to the crystal growth axis,the crystal conductivity and light response are better than those parallel to the crystal growth axis.Further analysis of its structure shows that BABI has a layered structure along the c-axis.When the channel direction of the strip electrode is parallel to the growth direction of crystal,the test results correspond to the interlayer properties of crystal;when the channel direction of the strip electrode is perpendicular to the growth direction of crystal,the test results correspond to the interlayer properties of crystal.The experimental results show that the quasi-one-dimensional quantum-well structure in the layer is beneficial to the transport of both carriers and photocarriers.The application of UV detector further expands the application potential of bismuth-based materials outside the visible light region.In Chapter five,we prepared two kinds of halogen terminal functional Ti3C2 based MXene,respectively bromine terminal Ti3C2(Br-Ti3C2)and iodine terminal Ti3C2(I-Ti3C2),and used them to compound with methylamine-bismuth bromine(MBB)and methylamine-bismuth iodine(MBI).The experimental results show that the composite strategy can effectively improve the photoelectric performance of MBB and MBI.First of all,MXene has good electrical conductivity,which significantly improves the conductive level of the device.Secondly,the electronegativity of MXene surface and its effect on photocharge separation of MBI or MBB were revealed by in-situ Kelvin potential atomic force microscopy(KPFM)test under light and dark conditions.Theoretical calculation also proves that halogen terminal-functionalized MXene is beneficial to charge separation of perovskite surface.Finally,combined with UPS results,it is further confirmed that halogen terminal-functionalized MXene is very beneficial to improve the photoelectric properties of bismuth perovskite through the regulated surface work function.In chapter six,the main research content and innovation points of this paper are comprehensively summarized,and then some problems and deficiencies existing in the current work are analyzed and put forward.Finally,the prospect of the next stage is given for these problems.These conclusions and innovations can provide useful references for other researchers. |
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