Magnetic field effect on singlet exciton fission: A sensitive probe of molecular level morphology in organic films

Singlet exciton fission, i.e., the splitting of a singlet exciton into two triplet excitons in molecular materials, has attracted great attentions due to its potential applications in organic photovoltaic devices. However, how solid-state features like molecular packing and orientation affect this process is still a subject of active investigation. Traditionally, it was thought that fast singlet fission should take place between neighboring molecules with ordered arrangement, while random molecular packing would present significant barrier to fission process. In order to test this opinion, we performed both time-resolved fluorescence decay measurement and steady-state magnetic field effect detection on the rubrene-based amorphous films. The obtained magnetic field effects on the overall fission rates indicated that the fission events could occur between disordered rubrene pairs. This finding is of great importance because it suggests that high singlet fission yield may be achieved in films with low crystallization quality, thus reducing the production cost for commercial organic photovoltaic devices.