Synthesis And Properties Of Novel Group 14 Elements Chalcogenide Photoelectric Materials

Chalcogenides,such as CdTe,CuIn_1-xGa_xSe₂（CIGS）,Cu₂ZnSnS₄（CZTS）FeS₂and other are ideal photoelectric materials with suitable band gaps,high absorptivities and high carrier concentrations.Among them,CdTe and CIGS have been successfully commercialized.Still,problems such as high cost,insufficient suppliment of raw materials and environment pollution,need to be solved before large-scale application.CZTS and FeS₂ are cheap and abundant.But their efficiencies are still low.Therefore,it is beneficial to design and synthesise new cost effective chalcogenide photoelectric materials.Group 14 elements are abundant,cost effective and environmental friendly.They can form different coordinations and diverse structures with chalcogen and favors the formation of new compounds.This work focus on designing and synthesizing new chalcogenides with high absorbtivity and adequate band gaps using14 group elements.We solved their structures and characterized their physical properties.1.Natural intermediate band compounds.In this part of work,several elements are selected to optimize the natural intermediate band electronic structures of group 14 element chalcogenides.6 new compounds are successfully synthesized and their structures and physical properites are characterized.1)Na₂ZnSnS₄（space group I-4）has been successfully synthesized.The structure derives from AgGaS₂ structure.Na⁺replaced Ag⁺ions,Zn²⁺and Sn⁴⁺replaced Ga³⁺ions.Optical measurements show that the compound has two absorption edges of 2.8eV and 3.7 eV.First principal calculation results showed that the intermediate band is dominated by Sn 4s orbital and S 3p orbital hybridization antibonding state.Second harmonic generation measurements show that its SHG effect is 0.9 times of that of AgGaS₂ in particle size range of 20–41?m.2)K_2.4Ga_2.4M_1.6Q₈（M=Si,Ge;Q=S,Se）were synthesized.The four compounds are isostructural（space group I 4/mcm）.The scaffolds of the compounds are[(Ga_0.6/M_0.4)Q_4/2]chains,which are separated by K⁺ions.The experimental band gaps of K_2.4Ga_2.4Ge_1.6S₈ and K_2.4Ga_2.4Ge_1.6Se₈ were 3.5eV and 2.7 eV,respectively.First-principles calculations of K_2/3Ga_2/3Ge_1/3Se₂ model showed that the Ge 4s and Se p orbitals formed an intermediate band.K_2.4Ga_2.4Ge_1.6S₈ glass showed wide transparent range from 0.6?m to 10?m and high soften-temperature of 533?C.3)Na₂In₂SnSe₆（space group Fdd2）has been synthesized.The structure features[InSe₃]corner sharing chains,which are bridged by isolated[SnSe₄]tetrahedrons to form a 3-dimensional framework.Na⁺ions reside in the channels of the framework.Optical measurements showed that the compound has two absorption edges of 1.4 eV and 2.1 eV.First principal calculation results revealed that the intermediate band is dominated by Sn 5s and Se 4p orbital hybridization antibonding state.Light reponse measurements showed that the current density increased from 13to 29 mA?cm^-2 when iluuminated.Photoelectrochemistry measurements show that the material is n type and showed obvious photoelectric response in hydrogen evolution tests.2.Iron based photoelectric materials.This part of work selected different elements to stabilize iron’six coordination to obtain large crystal field splitting energy of Fe d orbitals and appropriate band gaps.8 new compounds are successfully and their light response and physical properites are characterized.1)NaM_0.5Sn_0.5S₂（M=Fe,Mn）have been successfully synthesized using Na₂S₂flux.The two compounds are isostructural and crystallize in space group R-3m.The structure features[M_0.5Sn_0.5S₂]^-layers which are seperated by Na⁺ions.Optical band gaps of NaMn_0.5Sn_0.5S₂ and NaFe_0.5Sn_0.5S₂ are 1.5 eV and 0.7 eV,respectively.The current density of NaFe_0.5Sn_0.5S₂ increased from 0.2 mA?cm^-2 to 0.3 mA?cm^-2 under illumination at a voltage bias of 5 V.Magnetization measurements showed that NaFe_0.5Sn_0.5S₂ undergoes an antiferromagnetic transition at T_N=14 K.2)Ln₃M_0.5M’Se₇（Ln=La,Ce,Sm;M=Fe,Mn;M’=Si,Ge）and La₃Mn GaSe₇have been successfully synthesized using KI flux.The six compounds are isostructural（space group P6₃）and Fe and Mn are six coordinated in them.The strucutures features[LnSe₇]frameworks,which are interclated by[M_xSe₆]chains and isolated[M’Se₄]tetrahedrons.Optical measurements revealed that their band gaps are in the range from 1.13 to 1.37 eV.The current density of Ce₃Fe_0.5SiSe₇ increased by81?A?cm^-2（48%）under illumination.Sm₃Mn_0.5GeSe₇ and Sm₃Fe_0.5SiSe₇ compounds show anti-ferromagnetic phase transitions with Néel temperatures of 13K and 24K,respectively.