Emil Enache-Pommer

University of Houston

Advising Professor: Hugh Hillhouse
Project Title: Processing of Self-Assembled Nanostructured Thin Films
Major: Chemical Engineering, Mathematics

Introduction

One focus of the Hillhouse Group is to help facilitate the scale-up and manufacturing of nanostructured thin films by adapting known chemistry and self-assembly routes to work with existing processing technologies such as spin-coating, dip-coating, and spray-coating. These scalable processing techniques are standard technologies for the coatings industry. Spin-coating in particular is used pervasively in the manufacturing of integrated circuits to prepare uniform layers of controlled thickness over 12 inch silicon wafers. Traditional spin-, dip-, and spray-coated films consist of an amorphous or disordered structure. However, a maturing technology based on inorganic-organic self-assembly chemistry yields spin-coated or dip-coated nanostructured films with controlled nanoscale topology, composition, and thickness. While initially developed utilizing silica as the inorganic constituent, the self-assembly process is general for many metal oxides.

The fabrication of inexpensive photovoltaic devices requires the low temperature synthesis of high interfacial area semiconducting metal oxides. It may be possible to use the self-assembly templating mechanism discussed above to synthesize high interfacial area SnO2 films. However, the self-assembly phase behavior of this system has not been widely studied. Here, we would like to investigate the phase formation of several surfactant/SnO2 solutions (project description provided by prof. Hillhouse).

Objectives

  • Prepare a mesoporous* silica thin film using spin-coating. Mesoporous materials are porous materials with uniformly arranged pores having a diameter between 2 and 50nm.
  • Synthesize a spin coated SnO2 film with ordered mesopores and crystalline walls. The film will be used for the fabrication of a dye-sensitized solar cell.

Experimental Approach

Although the silica and tin oxide mesostructured materials have similar formation mechanisms, the synthesis paths are slightly different because of the high reactivity shown by the Sn-based precursors.

Synthesis method for mesoporous SiO2 films:

  • Prepare solution of ABA triblock copolymer in ethanol
  • Sol-gel solution of ethanol, HCl and Si(Oet)4 is prepared at low pH
  • Solutions are then combined and mixed
  • Thin films are prepared using spin-coating
  • The films are dried overnight
  • Calcination at 400-500oC
Synthesis method for mesoporous SnO2 films:
  • ABA triblock copolymer is dissolved in ethanol
  • SnCl4 is added to the solution with stirring
  • Thin films are prepared using spin-coating
  • The films are dried overnight
  • Calcination at 300-400oC
The techniques used to identify the structure of the synthesized materials are x-ray diffraction and transmission electron microscopy.

Research findings

  • Spin-coating is a good alternative to dip-coating for the preparation of thin films (results are similar but spin-coating is a quicker technique).
  • Using P123 as surfactant and SnCl4 as the inorganic precursor, mesostructured tin oxide thin films were prepared. The films were treated with water vapor. The stability of the structure upon calcination requires further investigation.