Multilayer Photosystem I Films within Porous Indium Tin Oxide Cathodes for Enhanced Photocurrent Generation

Abstract

Light-to-charge carrier converting proteins involved in oxygenic photosynthesis can be utilized in biohybrid photovoltaic electrodes, and have a wide range of applications in solar energy conversion. Photosystem I (PSI) is one of the two primary protein complexes involved in photosynthesis within plants, algae and cyanobacteria. Photosystem I (PSI) is capable of inducing directional electron transfer upon illumination. Further improvement of the photocurrent performance of both PSI cathodes and anodes is necessary for the implementation of these low-cost and low-impact devices for energy conversion. One route for improving electrode performance is to incorporate PSI into porous electrodes. In this study, indium tin oxide (ITO) nanoparticles were used to fabricate porous, translucent and conductive host electrodes for PSI. Mesoporous and macroporous ITO electrodes were prepared, characterized and modified with PSI. In comparison to planar PSI-ITO cathodes, both mesoporous and macroporous ITO cathodes were found to enhance photocurrent generation in the presence of the electrochemical mediator. The photocurrent produced by macroporous ITO cathodes, 42 ± 5 μA/cm2, is on par with other porous electrode studies and is the highest reported value for a PSI-ITO cathode. Additionally, macroporous ITO cathodes displayed, on average, a 112% greater photocurrent per active surface area, when compared to mesoporous cathodes. Larger pore sizes improve performance by achieving a higher PSI loading, increasing the active surface area, and taking advantage of the spherical diffusion of redox mediators within the pores. This work shows the capabilities of porous ITO electrodes for biohybrid PSI photovoltaics and discusses directions for further improvement; namely the continued development of structurally stable macroporous electrodes.