Organic Photovoltaics

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Ultrafast Probes of Free Charge Generation in Organic Photovoltaics

We have developed a series of time-resolved optical spectroscopy experiments that resolve different properties of bound and free charges, including the characteristic length scales associated with the key branching step.

Using ultrafast photoluminescence spectroscopy, we resolve emission from hot excitons prior to energetic relaxation. Ultrafast annihilation measurements show that their volume approaches 20 nm3, prior to localization induced by structural relaxation. Hot excitons are initially highly mobile and charge photogeneration occurs predominately via these states in competition with relaxation.

At low temperature, we are able to access a regime where all charge pairs are frozen out following the primary charge transfer step and recombine slowly via tunnelling. The exponential distance dependence of electron tunnelling provides a sensitive probe of the distance distribution of initial charge pairs. We show that the most efficient blends are associated with substantially longer initial charge pair distances, which points to an Onsager type model and may be linked to the delocalization of the primary excitation.

Finally, we have recently developed an entirely new method – transient grating photoluminescence spectroscopy. By addressing the major disadvantages of existing methods, our sensitive new broadband, low background technique shows promise for samples ranging from photovoltaics to proteins and DNA.

A talk by MacDiarmid PI Dr Justin Hodgkiss, Victoria University of Wellington

Venues

Victoria University of Wellington, AM103
University of Otago, please use Scopia Desktop
University of Auckland, Dept of Physics, L6 Building 303, Room 303 610, 38 Princes St
Massey University, please use Scopia Desktop
Callaghan Innovation – Gracefield Campus, C-Block Meeting Room
University of Canterbury – Psychology 164

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