Proceedings of nanoGe Fall Meeting 2018 (NFM18)
DOI: https://doi.org/10.29363/nanoge.nfm.2018.044
Publication date: 6th July 2018
We applied peak force based conductive scanning force microscopy (cSFM) to investigate local conductance differences in TiO2 anatase thin films. We found that the current perpendicular to the interface increased by two orders of magnitude after a UV-ozone (UVO) treatment. This increase in current is attributed to a reduction of oxygen vacancies at the surface after UVO-treatment. Cleaning, i.e. removal of hydrocarbons plays only a minor role.
Thin films of titanium dioxide (TiO2) are applied in electronics, e.g. thin film transistors, anode materials for Lithium ion batteries, photoanodes for water oxidation and as hole blocking layer in perovskite solar cells (PSC). TiO2 anatase films can have a lower conductance compared to electron blocking layers like P3HT, PCPDTBT and spiro-OMEOTAD [1]. Thus the conductivity of TiO2 films is crucial for the electron charge transport and it can limit the solar cell power conversion efficiency (PCE). Therefore, an improved conductance perpendicular trough this layer is highly desirable [2]. Various cleaning procedures were reported for anatase TiO2 thin films which result in an increase in PCE [3-7]. However, the cleaning mechanism and the local conductivity were not investigated in detail on a nanometer scale. We could show that the PCE of planar PSC can be increased by 2% to a maximum of 15.4% by a controlled UV-ozone (UVO) treatment. Finally, peak force based cSFM is stable for over 3 million singe force distance curves. This stability allows to compare cSFM current images quantitatively for differently treated samples.
References:
[1] T. Leijtens, et al., Adv. Mater. 2013, 25, 3227–3233.
[2] C. Liu, et al., ACS Appl. Mater. Interfaces 2015, 7, 1153–1159.
[3] L. Cojocaru, et al., Chem. Lett. 2015, 44, 674–676.
[4] F. Zhang, et al., Chem. Mater. 2016, 28, 802–812.
[5] X. Ma, et al., ChemPhysChem 2017, 1–9.
[6] W. Ke, et al., Nat. Commun. 2015, 6, 6700.
[7] I. S. Kim, et al., ACS Appl. Mater. Interfaces 2016, 8, 24310–24314.
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