Baran Group Meeting

Terry Lou Working principle of DSSC (1) Photo-excitation of dye (2) Injection of e- to semiconductor conduction band (CB) (3) e-transport through CB, TCO and external circuit (4) Electrolyte reduced at cathode (5) Dye regenerated by electrolyte (6) Cell voltage corresponds to AV between CB edge energy (Ec) and redox potential of electrolyte Unproductive pathway (→ lower n) - E vs NHE (V -0.5- Conducting glass TiO2 Injection Ec Dye-Sensitized Solar Cells Dye Electrolyte Cathode 2 S* 1 6 Maximum voltage hv Red Ox Mediator 5 Interception Diffusion 1.0 S%/S+ 3 0.5- Relaxation of dye molecule at excited state Recombination of e- in CB or TCO with electrolyte or oxidized dye - Trapping of e in semiconductor 10-3 s 10-13 s 10-12 s 10-11 10-12 s 10-8 s 10-2 s hv 104 s 12/I- 10-6 s 13/I- 10-5 s FTO TiO2 Sensitizer Redox mediator Strategies in optimizing DSSC - C Increase light absorbance Increase AV (by raising Ę or redox potential of electrolyte) Reduce recombination Reduce internal resistance (TCO, porosity of semiconductor and electrolyte) Achieve high stability and turnover of dye and electrolyte Materials development Transparent Conducting Oxide (TCO) Baran Group Meeting Jun 5, 2021 Indium tin oxide (ITO) – highly conductive, less chemically stable Fluorine-doped tin oxide (FTO) - less conductive, highly chemically stable Coated on glass or plastic substrates Semiconductor Nanostructured metal oxide Film thickness ~10 μm; nanoparticle diameter 10-30 nm; porosity 50-60% High porosity facilitates dye adsorption and regeneration, but reduces particle coordination and increases dead ends for e- transport (<1% dead ends in a 50% porous film; 31% in a 75% porous film) TiO2 - anatase > rutile Preparation of TiO 2 nanoparticles: . • • • Hydrolysis of Ti(OR) 4, then hydrothermal growth and crystallization Acid-catalyzed: better dye adsorption Base-catalyzed: slower recombination AcOH commonly used Deposition onto conducting glass: • Nanoparticle formulated in paste with polymer additives • Doctor blading or screen printing, then sintered at >450 °C • Porosity controlled by amount of polymer Coating of ultrapure TiO 2 shell (~1 nm) by treating with TiCl4 ZnO higher e mobility but lower chemical stability Other metal oxides (SnO 2, Zn2SnO 4, SrTiO 3, Nb2O5, etc.) are less efficient 3

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