Preparation And Photoelectric Properties Of Transition Metal Doped CuAlS₂ Chalcopyrites

The wide applications of CuInSe₂?CIS?and Cu?In,Ga?Se₂?CIGS?compound semiconductors in solar cells have stimulated the research interesting in metal doped chalcopyrites.Different kind of metal substitution in the wide-bandgap chalcopyrites can form shallow impurity levels to improve their electrical conductivity,or it can form intermediate band photovoltaic materials with deep level impurities to develop solar cells without In and Ga.CuAlS₂ has a wide bandgap which is suitable to introduceimpuritylevels/bands,formingpromisingintermediateband semiconductors and transparent conductive materials.Our work is to explore the optimal synthesis conditions of CuAlS₂ and transition metal doped CuAlS₂:TM?TM=Ti,V,Cr,Mn and Ni?and then to study their photoelectric properties.The crystals of CuAlS₂ and CuAl_1-x-x Mn_xS₂ were grown by chemical vapor transport.The polycrystalline thin films of CuAlS₂ and CuAl_1-x-x TM_xS₂ were prepared by sulfurization of multilayer metallic precursors.The crystal structure,surface morphology,chemical composition and photoelectric properties of CuAlS₂ and CuAl_1-xTM_xS₂ were characterized by X-ray diffraction?XRD?,scanning electron microscope?SEM?,energy dispersive X-ray spectroscopy?EDAX?,UV-Vis-Nir spectrophotometer and Physical Property Measurement System?PPMS?,respectively.The results are as follow:1.Polycrystalline CuAlS₂ films were prepared by sulfurization of multilayer Cu/Al recursors deposited using magnetron sputtering,and the effect of precursors on he sulfurization reaction was studied.The optimal synthesis condition of CuAlS₂ ilms is to sulfurize[Cu/Al]₈ metallic layers for 5 hours at 650?.It is a green, table and reliable preparation method without KCN,which is easy to control the toichiometric amount of films.2.The single-phase CuAl_0.96TM_0.04S₂?TM=Ti,V,Cr,Mn and Ni?polycrystalline ilms prepared by sulfurization of multilayer metallic precursors adopt the halcopyrite structure with the space group I-42d.Transition metal doping educes the optical band gap of CuAlS₂ film from 3.8 eV to about 3.3 eV. mpurity intermediate bands are found in the band gap of Ti,V,Cr and Ni doped uAl S₂.It suggests CuAlS₂:TM intermediate band photovoltaic materials with eep level impurities,which can be applied in high-efficiency solar cells.3.CuAl_1-xMn_xS₂ crystals were grown by iodine transport method.The electrical transport and photoelectric properties of samples were studied.It is found that they show semiconducting behaviors.Compared to undoped CuAlS₂,the largest conductivity and photosensitive of CuAlS₂:Mn crystals increase to 1.7 and 13folds,respectively.Mn doping improves the electrical conductivity of CuAlS₂,induces strong internal photoelectric effect,and retains the wide band gap?E_g³.3eV?,suggesting CuAlS₂:TM being promising p-type transparent conductive materials and photoelectric materials.