Binding energy of singlet excitons and charge transfer complexes in MDMO-PPV:PCBM solar cells

The influence of an external electric field on the photoluminescence intensity of singlet excitons and charge transfer complexes is investigated for a poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) diode and a bulk heterojunction of the PPV in combination with [6,6]-phenyl-C61 butyric acid methylester (PCBM), respectively. The experimental data is related to the dissociation probability derived from the Onsager-Braun model. In this way, a lower limit for the singlet exciton binding energy of MDMO-PPV is determined as (327 +- 30) meV, whereas a significantly lower value of (203 +- 18) meV is extracted for the charge transfer complex in a MDMO-PPV:PCBM blend.