Electrospray Ion Beam Deposition And Preparation Of Model Molecular Solar Cells Surfaces

Abstract

Studying the fundamental science of surface science of dye-sensitised solar cells requires placing complex molecules on surfaces in an ultra-high vacuum. Since most dye molecules are fragile and non-volatile to be deposited by thermal evaporation or sublimation technique, electrospray deposition was therefore explored as an alternative method. This thesis aims to work on developing the electrospray deposition technique to obtain high-quality monolayers in situ in high vacuum environments.

Image charge detection mass spectrometry (CDMS) has been used to measure the speed and charge distributions of molecular ions. Image charge drift tube measurements formed large clusters giving strong transient signals with a narrow velocity distribution of cluster sizes ranging from 300 ms−1 and 330 ms−1. The charge-to-speed relationship showed fitting with a 1/v2, meaning that all clusters have constant kinetic energy. In the case of the small clusters or individual molecular ions travelling through the drift tube, advanced electronics are required to see the weak signals hidden in the background noise.

The electrostatic ion deflector experiments, highlighting the capabilities of bending the ion beam in order to work towards separating two components of the beam, showed the formation of large clusters in the beam. These clusters have required a higher voltage in order to be deflected by the same amount based on SIMION simulations and a smooth range of charge distributions. Small molecular ions are worth studying in the future - via the discovery of low voltage range since these deflection experiments have concentrated on the high voltage regime. In the second section, the XPS measurements of defocussing experiments showed an incapability of the Einzel lens to diverge the beam over a large area on the sample, especially when the SIMION simulation achieved this. As well as, the defocussing experiment using a long tube exhibited the success of the Einzel lens to spread the beam over the entire sample. In the last section, AFM and optical images displayed the deposition of graphene oxide successfully with heterogeneous deposition coverage across the surface.

Dye-sensitisers adsorbed onto rutile TiO2 (110) were deposited in situ in UHV using electrospray deposition. Adsorption geometries and determining the dispersion of these molecules with this titanium surface were investigated using X-ray photoemission spectroscopy (XPS). The results of O 1s photoemission in the monolayer coverages showed that dye complexes bind onto TiO2 (110) by deprotonation of the carboxylic acid and phosphonic acid groups so that their oxygen atoms bond to titanium atoms of the substrate. Photoemission of C 1s, together with N 1s, indicated that the molecule is intact on the surface.