Evaluating the performance of inkjet-printed transparent anode in biological photovoltaic systems

This PhD is the first report of additive manufacturing poly(3,4-ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS) anode for biological photovoltaic system (BPV) using inkjet printing technique. For BPV to practically achieve its theoretical energy conversion efficiency several improvements in anode design are needed. In addition to electrical conductivity, long-term operation stability and biocompatibility, anode must homogenously distribute light to photocatalytic material (photosynthetic microbes) immobilized on its surface. Transparency is crucial to add dimension to the anode structure, thus, maximising the surface area for microbial attachment whilst upholding the same spatial area of the BPV device. Transparent conductive oxides (TCO) are widely used as anode in BPV research due to the co-existence of high electrical conductivity and optical transmission in the form of thin film. However, expanding the use at a large scale is difficult due to its brittle nature, scarce resources, and limited surface area. PEDOT:PSS as a highly flexible and printable material has successfully replaced TCO as the anode in optoelectronic devices. However, its potential has not been explored in bioelectrochemical systems beyond surface treatment. Before introducing a commercially viable novel transparent anode material in BPV, all performance aspects and impacts on system operation must be considered. A comprehensive analysis of the feasibility of the inkjet printed PEDOT:PSS anode for BPV application has previously been unexplored. For this PhD, an aqueous dispersion of PEDOT:PSS was formulated with different concentrations of additives in an effort to optimise the ink for microbial interaction. The inkjet printing process was set in place for developed inks to print PEDOT:PSS film. The printed PEDOT:PSS film was optimised for its quality and characterised for its optoelectronic properties before incorporating it as an anode in BPV. Bright field and confocal microscopy data were overlapped to quantify cell adhesion and viability on PEDOT:PSS film using Image J. The choice of substrate for inkjet printing PEDOT:PSS anode was made by simultaneously comparing different substrates for their wetting ability, aqueous stability and microbial adhesion. Plastic substrate was found to be more suitable for long-term BPV operations as it offers better adhesive stability in aqueous environment, while glass substrates presented challenges such as delamination and reduced microbial adhesion. The surfactant concentration and number of printed layers were tuned to achieve the desired sheet resistance value for enhanced electrical conductivity and optical transparency. The sheet resistance of inkjet printed PEDOT:PSS film decreased ranging between 55610 Ωsq-1 to 29.5 Ωsq-1 and 7799 Ωsq-1 to 5.8 Ωsq-1 with the higher surfactant concentration and number of printed layers indicating improved conductivity. Whereas the fabricated PEDOT:PSS film exhibited high optical transparency of approximately 97%. However, a trade-off exists between optical transparency, electrical conductivity, number of printed layers, and printing time. The evaluation of this trade-off among these parameters is essential to optimise the performance of the PEDOT:PSS film in the BPV application. Confocal laser scanning microscopy was used to test the viability of Synechocystis cells attached to the inkjet printed PEDOT:PSS film and a low (<1%) occupancy was noticed in all tested conditions. Surfactant and crosslinker were investigated as possible limiting factors to microbial adhesion, reducing surfactant concentration was found to increase occupancy (60%), crosslinker concentration seem to have no significant impact on microbial attachment. Whilst PEDOT:PSS failed to produce suitable results in this PhD, it is the first time that the potential utility of PEDOT:PSS as an anode is demonstrated for BPV application. A holistic view of major limitations halting inkjet printed PEDOT:PSS film successful integration in BPV as the anode is presented here focusing on biocompatibility, aqueous stability and current collector. It is suggested to further investigate PEDOT:PSS due to the promising turnability of its electrical conductivity and optical transparency. The findings from this PhD can contribute to improving power generation from BPV in the long-term future and systematic optimisation of the BPV device for reliable analysis in the short term.