Theoretical Study On Defects And Optical Properties Of Sb₂Se₃

antimony selenide（Sb₂Se₃）,is an inexpensive,nontoxic,and stable semiconductor with a suitable band gap（1-1.3 e V）,a high absorption coefficient and proper mobility of carriers（10 cm~2/V·s）and other good properties,being used as an absorber in the solar cells.Defects and doping inevitably exist in the synthesis process of semiconductor,playing an imperative role in improving the performance of thin-film solar cells.Although the existence and energy level depth of defects allow to be detected by defect level spectrometers,it does not explain that the defects are formed from what kind of element and the magnitude of the transition energy level.From microscopic point of view,the defect-free and defective Sb₂Se₃on the affect of electronic structure and optical properties are studied based on the first-principles,as well as a clear understanding of the basic properties helps to adjust performances and improve efficiency through foreign doping.The research task I have accomplished and the results obtained are as follows:1.We calculated the crystal structure,electronic structures,optical properties of Sb₂Se₃,and the density of states（dos）of all unequal positions of Sb and Se were considered.The valence band and conduction band near the Fermi surface are mainly composed of Sb-5p and Se-4p orbital electron filling.The band structure is an indirect band gap with a value of E_gi=0.953e V.When the photon energy is about 2.4 e V,[010],[001]and[poly]appear peaks,which originate from the electronic transition of Sb-5p orbital in the valence band to Se-4p orbital in the conduction band.2.The energy band structure of Sb₂Se₃was calculated based on the hybrid density functional theory（HSE06）,which was an indirect band gap with E_g=1.251 e V.Under Sb-rich condition,the formation energies of Sb _Se and Se _Sb are lower than those of V_Sb and V_Se,so that they are more easily formed.V_Sb exhibits the acceptor defects of shallow energy levels under both growth conditions,resulting from the main source of Sb₂Se₃being p-type.The peak of[010]is the largest,the peak of[001]is second,the peak of[100]is the smallest.3.The concentrations of Te incorporated Sb₂Se₃are 5%,10%and 15%,respectively.All system optimizations employ dispersion correction with Becke-Johnson damping factor（GD3-BJ）.In the visible light range,the absorption coefficient of Te-doped Sb₂Se₃ reaches 1.54×10~5cm^-1,which is able to meet the requirement of thin film application in solar cells.