(21e) Enhanced Thermoelectric Power in Photo-Modulated Porphyrin-Bi2Te3 Nanowire Hybrid Systems

Solar energy is perhaps the most abundant renewable energy source, but its conversion into electric power is still challenging for photovoltaic (PV) cells because they have not achieved efficiencies and cost that can that put solar cells in a competitive advantage. Porphyrins have become an attractive choice for dye sensitized solar cell (DSSC) applications because they are relative inexpensive materials, and they can reach acceptable photon-carrier generation efficiency. Porphyrins are photoactive within the ultraviolet to visible region which represent close to 50% of the entire solar spectrum energy. Incorporating a thermoelectric element to porphyrins could increase the overall efficiency by collecting the infrared (IR) radiation. Achieving a larger efficiency by collecting from the UV to IR spectrum is the motivation for a proposed ultra-wide solar spectrum photovoltaic-thermoelectric (PV-TE) solar power cell. The understanding of the Photo-thermoelectric effects and charge transfer characteristics for the proposed PV-TE solar cell is fundamental and covered in this work. The thermoelectric characterization of porphyrin deposited onto p and n-type Bi₂Te₃ nanowires under different illumination conditions is presented. We observed charge transfer across the Bi₂Te₃ nanowire-porphyrin interface under illumination and the temperature dependence of carriers recombination within the porphyrin. Furthermore, The Seebeck coefficient is substantially increased under white light illumination indicating that residual charge in the porphyrin modulates the carrier concentration in the Bi₂Te₃nanowires, but the electrical conductivity is not appreciable altered resulting in an enhanced thermoelectric power. Photo modulation of thermoelectric power in hybrid materials provides an alternative approach to enhance the thermoelectric figure of merit. 

This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Los Alamos National Laboratory (Contract DE-AC52-06NA25396) and Sandia National Laboratories (Contract DE-AC04-94AL85000).