  Dye-sensitized solar cells (DSSCs) have been highlighted as the promising
alternative to generate clean energy based on low pay-back time materials.
These devices have been designed to mimic solar energy conversion processes
from photosynthetic organisms (the most efficient energy transduction
phenomenon observed in nature) with the aid of low-cost materials. Recently,
light-harvesting complexes (LHC) have been proposed as potential dyes in DSSCs
based on their higher light-absorption efficiencies as compared to synthetic
dyes. In this work, photo-electrochemical hybrid devices were rationally
designed by adding for the first time Leu and Lys tags to heterologously
expressed light-harvesting proteins from Chlamydomonas reinhardtii, thus
allowing their proper orientation and immobilization on graphene electrodes.
The light-harvesting complex 4 from C. reinhardtii (LHC4) was initially
expressed in Escherichia coli, purified via affinity chromatography and
subsequently immobilized on plasma-treated thin-film graphene electrodes. A
photocurrent density of 40.30 \pm 9.26 \mu A/cm2 was measured on devices using
liquid electrolytes supplemented with a phosphonated viologen to facilitate
charge transfer. Our results suggest that a new family of graphene-based
thin-film photovoltaic devices can be manufactured from rationally tagged LHC
proteins and opens the possibility to further explore fundamental processes of
energy transfer for biological components interfaced with synthetic materials.
