Electronic Structure and Charge Separation at an Organic Photovoltaic Heterojunction

Gregory Dutton and Steven Robey

CSTL, NIST Gaithersburg, MD 20899.

The molecular donor-acceptor interface performs a critical function in the operation of organic photovoltaics as the sole site of charge separation.  Understanding the electronic structure and exciton/polaron dynamics at these interfaces is crucial for developing the knowledge of the relevant diffusion, dissociation and recombination processes necessary for achieving enhanced efficiencies.  We have employed photoemission techniques, primarily two-photon photoemission spectroscopy (2PPE) and time-resolved pump-probe measurements, to examine these issues for thin films and heterojunctions of copper phthalocyanine (CuPc) and C₆₀ fullerene.  We prepare model interfaces of ultrathin films on Ag(111).  Using a combination of visible pump, corresponding to the phthalocyanine Q-band absorption maximum, and UV probe, we observe the ultrafast population dynamics of the charge-separated C₆₀ LUMO electron-polaron.  Preliminary analogies of corresponding physical molecular structures at this interface will also be presented based on STM results for the similar zinc phthalocyanine/C₆₀ interface.

CATEGORY: Materials

Mentor:  Steven Robey

            Div. 837, CSTL

A129, Bldg. 217, MS 8372

Tel:     x8040

Fax:   

Email: gregory.dutton@nist.gov

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