Controlling film deposition via viscosity

(supervisor: Rudi Winter)

Nature of project: experimental, data analysis

Available to full-time physicists only.

Project description and methodology

Inorganic thin-film solar cells consisist of several layers of different functional materials. These typically include a rigid substrate, two electrodes, a light-collecting dye, and a hole-conducting charge transfer (electrolyte) layer. These layers are deposited by one of a number of different coating procedures including spin coating (very thin films), dip coating (thicker films from precursor solutions such as nano-particle inks) and doctor blading (thick films from pastes). In this project, we will investigate the dip coating process and the effect that the viscosity of the precursor ink (colloidal solution of CuInGaS2 particles) has on the resulting films. Viscosity depends strongly on temperature, but also on additives to the precursor solution. Suitable additives include high-viscosity liquids such as glycerol and particles such as nano-clay. The latter may also direct the deposition process crystallographically because the nano-scale clay platelets will show a strong preference to orientate themselves parallel to the substrate. The viscosity of the modified nano-particle inks will be measured using a rheometer.

A successful project will develop beyond the above in one/some of the following directions:
The resulting films will be characterised by microscopy techniques such as Atomic Force Microscopy with image analysis to identify morphological patterns.

When considering where to take your project, please bear in mind the time available. It is preferable to do fewer things well than to try many and not get conclusive results on any of them. However, sometimes it is useful to have a couple of strands of investigation in parallel to work on in case delays occur.

Additional scope or challenge if taken as a Year-4 project: The fourth-year version of the project takes the analysis of the

microscopy data a step further to quantify patterns and do a statistical analysis in terms of radial distribution and correlation functions.

Initial literature for students:

  1. Q Guo et al., Nano Lett 9 (2009) 3060
  2. L Zhang et al., J Colloid Interf Sci 378 (2012) 222
  3. TY Tsai et al., J Mater Chem 22 (2012) 13050

Novelty, degree of difficulty and amount of assistance required

This is a research project. The general effect of viscosity on film thickness and texture is known, but no quantitative data are available for the CuInGaS2 system under study.

Project milestones and deliverables (including timescale)

milestoneto be completed by
familiarisation with dipper and rheometerChristmas
sample preparation procedure establishedend of October
range of samples preparedend of February
rheological and imaging data takenEaster

Students taking this project will have to submit a full risk assessment form