Preparation Of SnO 2 -based Transparent Conductive Films By Sol-gel Method

Tin oxide?SnO₂?is tetragonal rutile structure and the band gap of SnO₂ is 3.5eV-4.0eV.The intrinsic conduction of undoped SnO₂ shows n-type semi-conductive character.Due to good conductivity,high visible light transmittance and strong stability,the SnO₂-based thin films are widely applied in the fields of transparent electrode,surface heating film,gas sensor,etc.In addition,SnO₂ is suitable for widely applying to industry and has become alternative materials to ITO?Indium Tin Oxide?because of their abundant resource,low cost,environment compatibilit.If we can get excellent photoelectric properties of SnO₂ films,it will be of great significance to replace ITO films and to expand the application fields of TCO?Transparent Conductive Oxide?films.In this paper,SnO₂ films were prepared by sol–gel method which used SnCl₂?2H₂O as doping precursor.At first,the basic conditions of experiment were determined.Then the SnO₂:Sb?ATO?,SnO₂:P,SnO₂:?Sb+P?and SnO₂:Al transparent conductive films were prepared,which used Sb,P and Al as doping elements.The influence of doping content,annealing temperature and coating times on optoelectrical properties of SnO₂ films were investigated.And the SnO₂ films were charactered by XRD?X-ray diffraction?,SEM?Scanning Electron Microscope?,AFM?Atomic Force Microscope?,UV-VIS?Ultraviolet–visible Spectroscopy?and Four-Point prode.Results showed that all types of SnO₂ films exhibited the tetragonal rutile structure.The doping elements mainly existed in SnO₂ crystal lattice with the form of substitution and interstitial ion.With the increase of Sb doping content from 5mol% to 11mol%,the grain size of ATO?Antimony Tin Oxide?thin films reduced,the RMS?Root Mean Square?roughness increased from 0.48 nm to 0.89 nm,the sheet resistance decreased first and then increased,and the average visible light transmittance decreased slightly.The ATO films prepared at a Sb/Sn ratio of 9mol%,at an annealing temperature of 450? for 30 min and in coating times of 12 C exhibited an optimal sheet resistance of 194?/?.In the experimental range,the average transmittance of ATO in the visible region could reach up to 80%.Compared with ATO thin films,SnO₂:P films had lower solubility,higher sheet resistance,and higher visible light transmittance.With the increase of P doping level from 1mol% to 3mol%,the grain size and crystallinity of SnO₂:P thin films decreased,the RMS roughness descreased from 1.33 nm to 0.59 nm,the sheet resistance decreased firstly and then increased,and the average visible light transmittance decreased slightly.To a certain extent,the sheet resistance of SnO₂:P films was obviously descreased with annealing temperature increased and with coating times increased.The SnO₂:P films had an optimal sheet resistance of 8.9 k?/? when P/Sn ratio was 2 mol%,coating times were 14 C and annealing temperature was 450? for 30 min.In the experimental range,the average visible transmittance could reach up over 90%.The sheet resistance and average visible transmittance of SnO₂:?Sb+P?transparent conductive films were between ATO films and SnO₂:P films.The optimal sheet resistance of SnO₂:?Sb+P?film was 983?/? when Sb doping comtent was 9mol% and P doping content was 1mol%.In the test range,the average visible transmittance could reach up to 85%.By preparing SnO₂:Al films,Al3+ replaced Sn4+ site in SnO₂ lattice to produce hole carriers.When the Al/Sn exceeded 8mol%,the hole concentration exceeded the electron and became the main carrier.The SnO₂:Al films changed from n-type conduction to p-type conduction.The SnO₂:Al films had an optimal sheet resistance of 18.4 k?/? when Al/Sn ratio was 14 mol%,coating times were 10 C and annealing temperature was 450? for 30 min.Compared with the n-type SnO₂ films,the curve of sheet resistance of SnO₂:Al films with Al-doping level was more complicated,the Al doping concentration of p-type SnO₂ films was higher,and the sheet resistance was higher.With the increase of Al doping level,the grain size and crystallinity of SnO₂:Al thin films decreased,and the RMS roughness was overall upward trend.The effect of annealing temperature and coating times on the photoelectric property of SnO₂:Al films had a similar effect with n-type SnO₂ films.