Singlet and Triplet Carrier Dynamics in Rubrene Single Crystal

We systematically investigate the singlet and triplet carrier dynamics in rubrene single crystal in the time scale from femtosecond (fs) up to microsecond (μs) using time-resolved and temperature-dependent photoluminescence (PL) techniques. Five PL bands were observed between 1.60 and 2.14 eV, and they are assigned to exciton peak, zero phonon intrinsic transition, and vibronic replicas, respectively. The ultrafast carrier scattering results in a broad distribution of hot carriers with a time constant as fast as 100 fs. The singlet fission and phonon scattering lead to 6.2 and 47 ps relaxation, respectively. The radiative recombination of singlet carriers exhibits wavelength-dependent lifetimes. The delayed fluorescence was observed on the microsecond time scale. The temperature-dependent and excitation intensity-dependent lifetime measurements confirmed that the delayed fluorescence is due to triplet–triplet annihilation that can be well described by rate equations of the triplet population.