Temperature-Independent Charge Carrier Photogeneration in P3HT-PCBM Blends with Different Morphology

The effect of temperature on the quantum yield for charge carrier photogeneration in P3HT-PCBM blend films was studied Using ultrafast transient absorption and microwave photoconductance techniques. The quantum yield was found to be virtually independent of temperature for time scales up to tens of nanoseconds after photoexcitation of P3HT. Implications of this observation for the mechanism of free charge carrier generation are discussed. The decay of charges due to recombination and/or trapping on longer times becomes faster at higher temperature, as a result of thermally activated electron and hole mobilities. The magnitude of the quantum yield depends oil the morphology of the blend film, which is determined by the spin-coating solvent and annealing conditions.