Composition formula of transparent conductive tin doped indium oxide in terms of cluster plus glue atom model

As transparent electrode, the tin (Sn) doped indium oxide (In2O3) film has been widely used in the photo-electric and electric-photo conversion devices. While, the relation between carrier concentration and Sn doping content in Sn doped In2O3 (ITO) film hasn’t be revealed satisfactorily enough. In this article, the so-called ‘cluster plus glue atom’ model was first used to describe In2O3 and ITO. Based on the definition rule of cluster, the principal and unit cluster formula of In2O3 were [In–O6]In3 and ([In–O6]In3)-([In–O6]In3)6-([In–O6]In3), respectively. Then, with the lowest Sn doping content, the unit cluster formula and composition formula of ITO could be expressed as ([Sn–O6]In3)-([Sn–O6]In3) ([In–O6]In3)5-([Sn–O6]In3) and Sn3In29O48, respectively. The unit cluster of ITO showed Sn/In atom ratio of 10.34 at.%, which corresponded well with that of commercial ITO material (10.30 at.%). Based on ITO unit cluster, the theoretical optimal value of ITO electron carrier concentration could reach 2.9 × 1021 (/cm3). Actually, the experimental value of electron carrier concentration of ITO was lower than 1/3 of the theoretical optimal one. The difference between theoretical optimal value and experimental value of ITO electron carrier concentration was discussed based on the unit cluster formula of ITO. Finally, with the better understanding of ‘cluster plus glue atom’ model, the new type of transparent conductive oxide materials could be designed and applied in future.