Hightlight Paper:

Properties of a Biophotovoltaic Nanodevice

Clean energy production is arguably the greatest challenge for achieving a sustainable society. A recent survey compares technologies for CO₂ free production of electricity, including hydropower, wind, geothermal, nuclear fission and fusion, biomass, solar, and ocean energy, concluded that solar power is the most promising candidate. The harvesting of CO₂ free solar energy can be divided into concentration of solar energy, for driving generators at the high end or produce heated water for domestic use at the low end, and photovoltaic (PV) conversion of solar energy to electricity.

There are mainly two contemporary strategies in PV, i.e., the production of electricity from sun light. One exploits solid state semiconductor properties of e.g. silicon, gallium arsenide, and copper indium diselenide, which are subject to photoexcitations whereby photo induced charge carriers, i.e., hole-electron pairs, are produced. The second approach is well represented by the Gratzel cell, which combines semiconductor properties of TiO₂ nanoparticles, coated with dye molecules which provide the photoelectrons. In this context, the present effort combines the two approaches. Thus, 30 nm anode-cathode spacing is invoked on a silicon chip by means of electron beam lithography, and self-assembled green fluorescent proteins (GFP) are employed as the dye molecules.

We demonstrate how a photoelectric current at zero external potential bias (ZEPB) develops in a submicron PV cell, employing a dielectric medium including enhanced green fluorescent protein EGFP molecules. Photoinduced hole-electron pairs were suggested to form on the GFP molecules, which would serve as electron sinks and sources with respect to the Fermi level of the metallic leads if the Fermi level was bracketed by the molecular HOMO-LUMO gap. The observed net current would result from symmetry breaking aggregation of GFP proteins, which display photon induced conductivity.

Figure 1: (a) Relative source-drain current versus wavelength for different gate voltages.(b) Absorption spectrum of the solvated GFP molecule.

Figure 2: (a) Current-voltage characteristics of the device at positive bias. The ohmic contributions to the total photocurrent are indicated by straight lines. The total photocurrents are in red and blue colors. (b) Current-voltage characteristics at negative bias. (c) Summary of current-voltage characteristics. The arrows indicate the direction of increased applied voltage (d) ZEPB source-drain current dependence on gate voltage.

Publication reference >> Z. G. Chirgwandi, I. Panas, L.-G. Johansson, B. Norden, M. Willander, D. Winkler, H. Ågren J. Phys. Chem. C, in press (2008)

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