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2017 Materials science lecture series: advanced materials - 6 December 2017

2017 Materials science lecture series: advanced materials - 6 December 2017
PRACTICAL

Dec 06, 2017 - 10.30 uur


Universiteit Hasselt

campus Diepenbeek

Agoralaan Gebouw D

3590 Diepenbeek

Lokaal Aula H4


CONTACT

de heer Rajesh RAMANETI

32-11-268818

rajesh.ramaneti@uhasselt.be


MRS/E-MRS joint student chapter, Hasselt University with IMO-IMOMEC: 2017 materials science lecture series: advanced materials.

Speaker: Dr. Hana Krysova - J. Heyrovsky Institute of  Physical Chemistry, Prague, Czech Rpublic.

Topic:  Diamond photocathodes for dye-sensitized solar cells

Chaired by: Prof. Dr. Ken Haenen, IMO-IMOMEC, Hasselt University

Wednesday 6 December 2017, 10:30 -12:30

Aula H4, Building D, Hasselt University, Campus Diepenbeek.

Abstract:

The sensitization of wide band-gap semiconductors to visible light is intensively studied in the area of n-doped electrode materials, such as TiO2 , which forms a basis for the dye-sensitized solar cell (DSC). The most successful material for an active photocathode is p-doped NiO, but the highest efficiency obtained so far for the p-DSC is low. The final goal is a tandem device (p,n-DSC) in which both electrodes are the photoactive semiconductors. The tandem cells are attractive due to their enhanced voltage, but these cells cannot rival the efficiencies of the optimized n-DSCs at the moment.

Among the alternative photocathode materials, the B-doped nanocrystalline diamond (BDD) can be considered a promising replacement of NiO. Diamond films made by CVD are attractive due to their excellent chemical and electrochemical stability, optical transparency and favorable electrical properties.

The donor-π-bridge-acceptor dye, 4-(bis-{4-[5-(2,2-dicyano-vinyl)-thiophene-2-yl]-phenyl}-amino)- benzoic acid (coded P1) is one of chromophores which is frequently used for the sensitization of p-NiO and of some other p-type semiconductors. Non-covalent anchoring of P1 to diamond was performed by two different methods. The first one was a two-step procedure, polyethyleneimine (PEI) was adsorbed on Hterminated BDD, and subsequently modified with P1 and the second novel strategy was direct covalent anchoring of P1 dye to the surface of H-terminated B-doped diamond electrode. The second procedure leads to improved efficiency, nevertheless, illumination of the P1 dye by 1-sun light causes also some degradation.

A light-harvesting efficiency of a monolayer of dye molecules on a flat surface of B-doped nanocrystalline diamond is inherently small. Similar tests were performed with B-doped diamond electrodes sensitized with CPDT-Fur and BT-Rho dyes.The growth of nano-textured mesoporous diamond films was attempted by templating with SiO2 fibers and SiO2 spheres. So called nanodiamond foam was grown by using SiO2 spheres (500 nm in diameter) as templates, on which a thin BDD layer was deposited by standard chemical vapour deposition growth.

To directly compare flat diamond films and diamond foams, the diamond foams were sensitized with the same dyes as applied on flat BDD films. The prepared materials were tested as electrodes in the dark and upon illumination in an aqueous electrolyte solution with methyl viologen acting as a reversible electron acceptor. Reference experiments were carried out with standard flat BDD films, too. Cathodic photo-current densities for a fresh foam electrode sensitized with both CPDT-Fur and BT-Rho illuminated by white light are approximately 3 times larger than those on flat diamond, which is attributed to the enhanced surface area of the foam electrodes.