A novel experimental and mathematical method has been developed to directly characterise the dipole energy with a resolution up to 0.05eV by applying multiply insitu-spectroscopy. The work yields an insight into the intermediate energy states at the metal oxide/polymer layer interface and a prediction to the charge transport of the organic device.

In our work, the characterisation of chemical properties (XPS) and concentration distribution (NICISS)^[2] on a P3HT:PC₆₁BM Bulkheterojuction (BHJ) system with the high workfunction(ɸ) metal transparent oxides (MoO₃) thickness from 0.1nm to 8nm arises an observation of energy shift of polymer and heavy diffusion of MoO₃. Thus a hypothesis of dipole forming at the interface has been proposed.

Gradual changes of both WF(ɸ) and E_VB were observed when applying UPS and MIES upon the samples. Decomposition to the valence electron spectra of UPS by using Singular Value Decomposition (SVD)^[3] yields the characterisation of pristine MTO/BHJ and BHJ spectra with various energy shifts. The spectra were further processed with a deconvolution algorithm. A series of BHJ spectra with energy shift have been quantified, which forms energy ladders at the interface. We successfully reconstructed the energy levels of the MTO/polymer BHJ interface with the electronic parameters based on the evaluation of the UP spectra. The quantification of dipole energy with a range of MTO deposition thickness has been achieved and the mechanism of charge transport over the metal oxide/polymer layer interface was thus decrypted.

We also observed difference of dipole energy among MoO₃, V₂O₅ and WO₃ on BHJ. Treatments such as air exposure and annealing further alter the dipole energy, leading to a different charge transport mechanism. The performance of polymer-based devices such as OPV and OLED can thus be influenced

1. Yanting Yin, A.S., Jamie Quinton, David A. Lewis and Gunther G. Andersson, The Observation and Characterization of Dipoles forming at the MoO3-P3HT/PCBM BHJ Interface (ready for submission). 2018.

2. Andersson, G. and C. Ridings, Ion scattering studies of molecular structure at liquid surfaces with applications in industrial and biological systems. Chem Rev, 2014. 114(17): p. 8361-87.

3.Berlich, A., Y.-C. Liu, and H. Morgner, Growth of nickel nanoparticles on NiO/Ni(001): Evidence of adsorbed oxygen on metal particles by metastable induced electron spectroscopy (MIES). Surface Science, 2008. 602(24): p. 3737-374