Drop-casted Photosystem I/cytochrome c multilayer films for biohybrid solar energy conversion.

Abstract

One of the main barriers to making efficient Photosystem I-based biohybrid solar cells is the need for an electrochemical pathway to facilitate electron transfer between the P700 reaction center of Photosystem I and an electrode. To this end, nature provides inspiration in the form of cytochrome c6, a natural electron donor to the P700 site. Its natural ability to access the P700 binding pocket and reduce the reaction center can be mimicked by employing cytochrome c, which has a similar protein structure and redox chemistry while also being compatible with a variety of electrode surfaces. Previous research has incorporated cytochrome c to improve the photocurrent generation of Photosystem I using time consuming and/or specialized electrode preparation. While those methods lead to high protein areal density, in this work we use the quick and facile vacuum-assisted drop-casting technique to construct a Photosystem I/cytochrome c photoactive composite film with micron-scale thickness. We demonstrate that this simple fabrication technique can result in high cytochrome c loading and improvement in cathodic photocurrent over a drop-casted Photosystem I film without cytochrome c. In addition, we analyze the behavior of the cytochrome c/Photosystem I system at varying applied potentials to show that the improvement in performance can be attributed to enhancement of the electron transfer rate to P700 sites and therefore the PSI turnover rate within the composite film.