The Fundamental Research Of SnS/In₂S₃ Heterojunctions

Tin sulfide?SnS?thin films are orthorhombic compound semiconductors,and usually exhibit a p-type conduction.The optical band gaps of SnS films vary from 1.1 to 1.5 eV.SnS thin films have large optical absorption coefficient(>104 cm^-1)and a high power conversion efficiency?up to 25%?.The constitute elements of SnS are abundant and non-toxic.Therefore,SnS thin films have a wide application prospect as solar cell absorption layers.In this thesis,the metal elecrode,the SnS thin films and indium sulfide?In₂S₃?thin films were prepared by thermal evaporation.The influences of the thermal annealing conditions on the phases,structure,morphology,optical and electrical properties of the thin films were investigated.The SnS/In₂S₃ heterojunctions with rectification characteristic were fabricated.The energy band structure of SnS/In₂S₃ and the influences of the annealing conditions on the rectification characteristic were discussed.The main results were obtained as follows.1.The fabrication processes of SnS and In₂S₃ films were investigated.The electrical properties and phases of the SnS films are sensitive to the annealing conditions.When the annealing temperature is between 250? and 300?,there is an impurity phase?SnS2?in the SnS films.With the increasing of annealing temperature from 250 ?to 300 ?,the carrier concentration is increased gradually,and the resistivity is decreased.When the annealing temperature is 350?,the main phase of the films is Sn2S3,and the carrier concentration of the SnS films is decreased gradually with increasing the annealing time.The SnS films have the best optical and electrical properties at an annealing condition of 300? and 1.5 h.The optical band gap,carrier concentration,resistivity and mobility of SnS thin films are 1.48 eV,8.93 × 15 cm^-3,638 ?·cm and 1.10 cm2·s-1· V-1 respectively.In₂S₃ films have the best optical and electrical properties at an annealing condition of 300? and 1 h.The optical band gap,carrier concentration,resistivity and mobility of In₂S₃ thin films are 2.16 eV,6.53×1017cm^-3,9.56 ?· cm and 3.52 cm2·s-1·v-1,respectively.2.The Ohmic contact characteristics of Ag,Cu,ITO with the SnS thin films and Ag,ITO,AgIn with the In₂S₃ thin films were investigated under different annealing conditions.The results show that ITO/In₂S₃ and Ag/In/SnS have a good Ohmic contact.ITO/In₂S₃/SnS/In/Ag is a proper structure for the following heterojunction device fabrication and further research.3.SnS/In₂S₃ heterojunctions with rectification characteristic were fabricated.The energy band structures of SnS/In₂S₃ heterojunction and the photoelectric properties of them were studied.The influences of the annealing conditions and the thicknesses of In₂S₃ buffer layers on the SnS/In₂S₃ heterojunctions were discussed.The conduction band offset ?Ec of SnS/In₂S₃ heterojunction is-0.2 eV,which is slightly lower than the ideal value of ?Ec?0 eV<?Ec<0.4 eV?.This band offset alignment will lower the open circuit voltage and fill factor.4.The performances of SnS/In₂S₃ heterojunction solar cells were simulated by the software "wxAMPS".The conversion efficiency was obtained to be 4.8%by simulating the practical device.Through the simulation,we have obtained the following results:The optimum thickness of SnS absorber layer is 2 ?m.The thickness of In₂S₃ buffer layer should be deposited as thinner as possible.The optimum carrier concentrations of SnS and In₂S₃ thin films are 1019 cm^-3 and 1014-1015 cm 3,respectively.The optimum working temperature of the device is at room temperature conditions?300 K?.