HOPV12 - Blogs

4 th Hybrid and Organic Photovoltaic Conference -Uppsala 2012 250
C113 - A monte carlo study of increased charge mobility in molecular hole
transporters due to coulomb traps
Daniel Staff, Alison Walker
University of Bath, University of Bath, Bath, BA2 7AY, GB
In the construction of Solid State Dye Sensitized Solar Cells, the addition of redox inactive
ionic dopants such as Li-TFSI salt to molecular hole transporters increases the hole mobility 1 .
Consequently these cells gain efficiency as holes move away from the interface between the
mesoporous TiO2 film acting as electron acceptor and the hole transporter more rapidly and
are extracted more readily, reducing recombination. To understand the mechanisms behind
the increased hole mobility, we have developed a Monte Carlo model of charge hoping. The
hopping sites are potential wells around the anion sites caused by an attractive electrostatic
potential. We observe a similar order of magnitude increase in mobility with dopant
concentration of a form like that of a insulating/conducting phase transition when the
concentration of anions exceeds some critical value. The transition is typified by a change from
nearest neighbor site to site hopping and long waiting times in isolated traps to hoping directly
between traps with short waiting times in each trap.
References
[1] Snaith, H.; Grätzel, M. "Enhanced charge mobility in a molecular hole transporter via addition of redox inactive
ionic dopant: Implication to dye-sensitized solar cells". Appl. Phys. Lett. 89, 262114 (2006).
© SEFIN 2012