Characterization of Enzymatically Synthesized Titania Thin Films Using Positron Annihilation Spectroscopy Reveals Low-Cost Approach for Organic/Inorganic Photovoltaic Cells
E.F. van Amelrooy (Student TU Delft)
H. Schut (TU Delft - RST/Neutron and Positron Methods in Materials)
W. Egger (University of the Federal Armed Forces Munich)
Marcel Dickmann (Technische Universität München)
Christoph Hugenschmidt (Technische Universität München)
L. Mallée (TU Delft - BT/Biocatalysis)
Ulf Hanefeld (TU Delft - BT/Biocatalysis)
D.G.G. McMillan (TU Delft - BT/Biocatalysis)
SWH Eijt (TU Delft - RST/Fundamental Aspects of Materials and Energy)
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Abstract
A new method is developed to produce mesoporous titania thin films at room temperature using the enzyme papain in a dip-coating procedure, providing low-cost titania films in a sustainable manner. Quartz crystal microbalance, positron annihilation Doppler broadening and lifetime spectroscopy, scanning electron microscopy, and X-ray diffraction are used to determine the deposition and structural properties of the films. As-deposited films have low densities ρ ≈ 0.6 g cm−3, contain small micropores and proteins, and exhibit corrugated surfaces. Annealing at temperatures of 300 °C or higher leads to the destruction and evaporation of most of the organic material, resulting in a thickness decrease of 50–60%, more pure titania films with increased density, an increase in micropore size and a decrease in the concentration and size of atomic-scale vacancies. Up to 50 layers could be stacked, allowing easy control over the total layer thickness. Based on these titania films, first test devices consisting of natural dye-sensitized solar cells are produced, that show photovoltaic activity and indicate possibilities for low-cost, accessible, organic production of solar cells. Given the wide range of other applications for titania, this new method is a promising candidate for improving the fabrication of those products with respect to cost, sustainability, and production speed.