Triplet and singlet exciton diffusion in disordered rubrene films: implications for photon upconversion.

Triplet and singlet exciton diffusion plays a decisive role in triplet-triplet annihilation (TTA) and singlet fission (SF) processes of rubrene (Rub) films at low excitation power, and therefore has an important implication for TTA-mediated photon upconversion (UC). Although triplet diffusion in crystalline Rub was studied before, there is no quantitative data on diffusion in disordered Rub films most widely employed for NIR-to-Vis UC. The lack of these data hinders the progress of TTA-UC applications relying on a Rub annihilator (emitter). Herein, a time-resolved PL bulk-quenching technique was employed to estimate the exciton diffusion coefficient (