Electronic and chemical properties of ZnO in inverted organic photovoltaic devices

Sharma, Anirudh; Franklin, Joseph B.; Singh, Birendra; Andersson, Gunther G.; Lewis, David A.

Electronic and chemical properties of ZnO in inverted organic photovoltaic devices

Type

Article

Authors

Sharma, Anirudh
Franklin, Joseph B.
Singh, Birendra
Andersson, Gunther G.
Lewis, David A.

Date

2015

Abstract

Photo-conversion efficiency of inverted polymer solar cells incorporating pulsed laser deposited ZnO electron transport layer have been found to significantly increase from 0.8% to up to 3.3% as the film thickness increased from 4 nm to 100 nm. While the ZnO film thickness was found to have little influence on the morphology of the resultant ZnO films, the band structure of ZnO was found to evolve only for films of thickness 25 nm or more and this was accompanied by a significant reduction of 0.4 eV in the workfunction. The films became more oxygen deficient with increased thickness, as found from X-ray photoelectron spectroscopy (XPS) and valence band XPS (VBXPS). We attribute the strong dependence of device performance to the zinc to oxygen stoichiometry within the ZnO layers, leading to improvement in the band structure of ZnO with increased thickness.

Citation

Sharma, A., Franklin, J. B., Singh, B., Andersson, G. G., & Lewis, D. A. (2015). Electronic and chemical properties of ZnO in inverted organic photovoltaic devices. Organic Electronics, 24, 131–136. doi:10.1016/j.orgel.2015.05.032

Acknowledgements

Authors would like to acknowledge Rantej Kler for helping in measuring the transmission function of the spectrometer, for quantitative XPS analysis. A.S. wishes to acknowledge Flinders University for postgraduate research scholarship and CSIRO for PhD studentship. This work has been supported by the CSIRO Manufacturing Flagship and by the School of Chemical and Physical Sciences of Flinders University. JBF gratefully acknowledges King Abdhullah University of Science and Technology (KAUST) - Imperial College Academic Excellence Alliance for research support and would like to thank Peter Petrov (Imperial College London) for access to PLD facilities in the Thin Film Laboratory, Imperial College.