Here, a new design for natural dye-sensitized solar cells is presented. A stacked assembly consisting of a discrete Photosystem I protein multilayer film atop a natural dye-sensitized photoanode expands absorbance of the solar spectrum to facilitate a more than 2-fold increase in cell photovoltage relative to the unmodified equivalent.

The design of electrode interfaces to achieve efficient electron transfer to biomolecules is important in many bioelectrochemical processes. Within the field of biohybrid solar energy conversion, constructing multilayered Photosystem I (PSI) protein films that maintain good electronic connection to an underlying electrode has been a major challenge. Previous shortcomings include low loadings, long deposition times, and poor connection between PSI and conducting polymers within composite films. Here, we show that PSI protein complexes can be deposited into monolayers within a 30 min timespan by leveraging the electrostatic interactions between the protein complex and the poly­(3,4-ethylenedioxythiophene)-polystyrenesulfonate (PEDOT:PSS) polymer. Further, we follow a layer-by-layer (LBL) deposition procedure to produce up to 9-layer pairs of PSI and PEDOT:PSS with highly reproducible layer thicknesses as well as distinct changes in surface composition. When tested in an electrochemical cell employing ubiquinone-0 as a mediator, the photocurrent performance of the LBL films increased linearly by 83 ± 6 nA/cm2 per PSI layer up to 6-layer pairs. The 6-layer pair samples yielded a photocurrent of 414 ± 13 nA/cm2, after which the achieved photocurrent diminished with additional layer pairs. The turnover number (TN) of the PSI–PEDOT:PSS LBL assemblies also greatly exceeds that of drop-casted PSI multilayer films, highlighting that the rate of electron collection is improved through the systematic deposition of the protein complexes and conducting polymer. The capability to deposit high loadings of PSI between PEDOT:PSS layers, while retaining connection to the underlying electrode, shows the value in using LBL assembly to produce PSI and PEDOT:PSS bioelectrodes for photoelectrochemical energy harvesting applications.