Abstract

It is becoming increasingly apparent that films of regioregular poly(3-hexylthiophene) [RR- P3HT ] are one of those rare cases in organic semiconductors where absorption of photons leads to high yields of ‘instantaneously’ photo-generated charges. Of course neutral singlet excited states are also formed, but with the neutral singlet state absorption peak at 1200 nm, greatly red-shifted against the polaron peak at 800 nm, this offers an ideal opportunity for femtosecond optical pump-probe measurements to study the behaviour of polarons in P3HT without worrying about interference from the singlet state. Here we will look at the kinetics of charge (polaron) generation and recombination in films of RR-P3HT as a function of; laser power, excitation wavelength and pulse repetition rate, and we will calculate the efficiency of polaron formation per absorbed photon in P3HT . We describe a model to explain the laser power dependence of the P3HT polaron recombination kinetics (which gives us some insight into charge recombination in organic solar cells and light emitting diodes), and have a crack at explaining the mechanism of charge generation itself and why it’s so high in P3HT . This work is as yet unpublished and this will be the first talk given on the new photophysics outside Japan.