Protonic processes that occur in water in the dark are identical to electronic processes that occur in semiconductors in the dark; for this reason, our group defines water as a protonic semiconductor. Using this fact, over a half-century ago Prof. John Bockris demonstrated that hydrated bipolar ion-selective polymer membranes form ionic diodes. Our group has since coupled this discovery with photoacid dye sensitization, pin-type doping, and fabrication of membrane–electrode–assemblies (MEA) to demonstrate photovoltaic action and open-circuit photovoltages of ~50 mV. These innovations were important because they enabled the energy in photons to release protons (photoacids), ease of fabrication (pin-type doping), and using reversible H 2 redox chemistry protonic was directly transduced into electronic current (the MEA) so that it could be measured using a common potentiostat. For my presentation I will report on the effects of fabrication parameters on the properties of the previously described ion-exchange membrane-based protonic solar cells. The fabrication parameters chosen to be varied were the thickness of the i-layer, thickness of the integrated catalyst/electrode layer, and annealing conditions of the MEA. Current density versus potential curves were then collected to determine the open-circuit photovoltage and short-circuit photocurrent values for each sample, and electrochemical characterization was performed to determine the effect of each fabrication parameter on the depletion width, carrier density, and presence of trap states at interfaces in the device. Lastly, scanning electron microscopy was used to visualize the effect of fabrication parameters on the architecture of resulting devices and to correlate physical structure and composition with photovoltaic performance. The fine control exerted during fabrication of ion-exchange membrane-based solar cells allows for a meaningful comparison between the physical phenomena at play in these new functional protonic materials and in traditional, electron-based semiconductor solar cells. This study also identifies guiding fabrication principles which will be crucial in the production of protonic solar cell devices with maximum efficiency. Lastly, projections of ideal performance for this technology described at the end of this work facilitate a discussion of its techno-economically relevant applications.

Role of fabrication parameters on the properties of purely protonic solar cells composed of photoacid-modified ion-exchange membranes

2019 Fall National Meeting

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