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

Abstract

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...

Bulk Heterojunction Upconversion Thin Films Fabricated via One-Step Solution Deposition

“…However, as the rubrene film PL lifetime is highly sensitive to the film morphology and crystallinity, we compared the BHJ sample to the spin-coated rubrene film while the bilayer sample is compared to the evaporated rubrene film. The crystallinity of the rubrene could have a significant effect on the upconversion performance . Additionally, the rubrene HOMO energy level has been shown to change with crystallinity, altering the energy level alignment between donor and acceptor. , Even though the spin-coated and evaporated rubrene films have very similar PLQY, absorption spectra, and emission spectra, the lifetimes of these two films are very different.…”

“…The crystallinity of the rubrene could have a significant effect on the upconversion performance. 57 Additionally, the rubrene HOMO energy level has been shown to change with crystallinity, altering the energy level alignment between donor and acceptor. 58,59 Even though the spin-coated and evaporated rubrene films have very similar PLQY, absorption spectra, and emission spectra, the lifetimes of these two films are very different.…”

Tailoring the optical properties of rubrene films through epitaxy-induced amorphous-to-crystal transition

“…59,60 Instead, the dominant source of PL quenching can be identified as the spontaneous amorphous-to-crystal transition discussed above since an increase of the crystallinity of RUB should translate into enhanced singlet fission. 12,61 In RUB crystals and polycrystalline films, SF occurs with near-unit efficiency, leading to a relatively low PL quantum yield (of the order of a few percent) [61][62][63] with a substantial fraction (490%) 4 of the PL originating from triplet fusion, which enables the partial conversion/recycling of dark triplets to bright singlets. In contrast, an order of magnitude higher PL quantum yield is obtained in amorphous RUB films, where the molecules are randomly oriented, or in matrices with diluted RUB molecules, 12,63 where SF is suppressed.…”

Efficient Spin Interconversion by Molecular Conformation Dynamics of a Triplet Pair for Photon Up-Conversion in an Amorphous Solid

“…We thus used d = 0.7 nm, which was the intermolecular distance along the b axis of a rubrene single crystal . According to previous reports, ,, D T for the triplet exciton in amorphous rubrene is 10 –6 –10 –7 cm 2 s –1 while D T in the single crystal rubrene is 10 –4 –10 –5 cm 2 s –1 . By using these reported parameters, we estimate that k hop is 0.12–1.2 ns –1 for amorphous rubrene and 12–120 ns –1 for single crystal rubrene, respectively.…”