I am always confused when i have to compare energy levels of my molecules with the energy level of ITO (Indium Tin Oxide). Different papers in literature report different energy level. Some papers report 4.7 and other 4.8eV and even 5.2eV. Which should be considered as correct.
The work function of ITO is around ~4.8eV. However, it also depends on how it is prepared like presence of oxygen during deposition and annealing temperature. In addition, some after treatment of prepared film is also responsible for change in work function such as ozone treatment is believed to increase the work function.
http://www.sciencedirect.com/science/article/pii/S0379677908003925
Dear Gopal,
Adding to what has been said ,the energy gap of the material depends on its chemical structure. In case of ITO it is the Stoichiometry of the resulting structure in the sense the ratio of one to 1 for the indium and tin. Based on this fact,the band gap is engineered in the compound semiconductors by changing its mixing rations such as Gax Al 1-x AS and many other compounds.
The other factor that can affect the energy gap is the grain size of the deposited material. It is so that the band-gap increases as the the grain size decreases.
For the effect of grain size on the band gap please see the link: http://arxiv.org/pdf/1207.2830.pdf
as an example.
The grain size and the stoichiometry depends on the deposition condition.
Therefore this variation on the data of ITO films.
Agreeing to earlier answers, I can add that while depositing the environmental condition and thickness may differ. With higher thickness the porosity may be minimised so that conductivity is higher.
If the work function is determined experimentally then experimental error depending on the applied method has to be taken into account. Such error can be as high as few tenths of eV, therefore variations of +/-0.1-0.2 eV in the reported value of work function may result not only from variations in chemical structure or morphology of the layer but also from such experimental error.
This variation is experimental and depends of the contact potential difference betweeen the tip and ITO surfaces. In the paper Interfacial electronic structures in an organic light-emitting diode (S. T. Lee, Appl. Phys. Lett., Vol. 74, No. 5, 1 February 1999) have more details.
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