The reported values of energy gap of CZTS thin films are in the range 1.4-1.5 eV, however, my spray pyrolysis deposited CZTS thin films have more than 2 eV energy gap. What are the possible reasons for these high values?
Most likely its because of ZnS present in your sample. Try using UV-Raman for checking ZnS presence. Quantum confinement is hard to believe in case of spray pyrolysis films
There are two possibilities that I can think of. Either phase separation, i.e. the film is a mixture of your reactants rather than true CZTS, or the crystals are very small and you have quantum confinement effects. You might be able to use XRD to test the former, and SEM/ TEM to test the latter.
http://pubs.rsc.org/En/content/articlepdf/2013/ta/c3ta00357d
This paper shows the effect that quantum confinement has on CZTS. They say that 3 nm nanoparticles give a band gap of approximately 1.8 eV. To see stuff on this scale you'll need TEM, or possibly a high resolution AFM.
Most likely its because of ZnS present in your sample. Try using UV-Raman for checking ZnS presence. Quantum confinement is hard to believe in case of spray pyrolysis films
Band gap engineering depends on different effects such as quantum confinement. Other possibilities are using impurities of either types (donors or acceptors).
have you checked the AFM of these films
if the average diameter is less than 100 nm
then you must except the fact of the increase in energy gap
@nadir...
I think the effect of size dependant band gap is usually below 10-15 nm, this is because of domain or particle size reaching closer to electronic shells (bohr radius). Can you please provide any literature on this effect observed below 100 nm. This is new to me.
It depends what solutions, precursors and deposition conditions like carier gas (N2 or air) are used. In your system Sn4+ is extremely hydrolysable cation. So oxygen contained phases may be presented in CZTS films prepared by CSP.
There are many influencing factors for band gaps of material and depends up on the fabrication approach as well. In the case of spray deposition, the band gap of material can be influenced by crystal quality, phase purity and oxygen incorporation. One possible reason is, oxygen can be coexisted in the form of CZT(SO) form which results in electronic interaction and change in Eg.
You can find some hints elsewhere;
1. http://pubs.acs.org/doi/abs/10.1021/jp503678h
2. http://pubs.rsc.org/en/content/articlehtml/2013/ce/c3ce41387j, CrystEngComm, 2013, 15, 10500-10509.
Dear Bakr,
You know that the thickness of the films has critical role in the band gap of the films. In our previous studies related with the CuInS2, we have proved that the thickness of the films changes optical properties as well as the structural and electrical properties remarkably. I think your conditions would be related to the thickness of the CZTS films. If you like to see more, you can explore our following articles.
All the best.
Article Effect of Thickness on the Film Properties of Spray Deposite...
Article Preparation and characterization of cost effective spray pyr...
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