NIR-to-vis photon upconversion in rubrenes with increasing structural complexity

Abstract

Rubrene is the most widely used triplet-triplet annihilation (TTA) emitter for NIR-to-vis photon upconversion (UC), however, strong singlet fission (SF) in the solid films quenches its emission and hampers practical...

In optimized rubrene-based nanoparticle blends for photon upconversion, singlet energy collection outcompetes triplet-pair separation, not singlet fission

“…18,26,28 Similar to single crystals, singlet fission dynamics and delayed PL arising from triplet fusion have been reported in rubrene thin films, though the time constants measured vary widely and there is a clear dependence on sample morphology. 25,30,46–51 In particular, truly amorphous thin films show no evidence of singlet fission: the photoluminescence decays exponentially with a time constant of 15.2 ns, 48 matching the radiative lifetime of singlet excitons in solution. 68 Even thin films that give no peaks in X-ray diffraction experiments exhibit singlet fission dynamics, 46,47 suggesting that favourable molecular packing on a local scale can give rise to site-specific singlet fission.…”

“…As a result, several strategies have recently been reported to mitigate the effects of singlet fission in solid rubrene-based TTA-UC systems. The addition of bulky side groups to increase intermolecular distances has been shown to improve the PLQY of rubrene several-fold, 26,29,30 though the benefit to TTA-UC is severely tempered by reduced triplet diffusivity. 30 More commonly, rubrene is doped with the singlet energy collector tetraphenyldibenzoperiflanthene (DBP), which can harvest singlet energy from rubrene by Förster resonance energy transfer (FRET).…”

“…The addition of bulky side groups to increase intermolecular distances has been shown to improve the PLQY of rubrene several-fold, 26,29,30 though the benefit to TTA-UC is severely tempered by reduced triplet diffusivity. 30 More commonly, rubrene is doped with the singlet energy collector tetraphenyldibenzoperiflanthene (DBP), which can harvest singlet energy from rubrene by Förster resonance energy transfer (FRET). 18,26–28 The effectiveness of this strategy appears to vary significantly with the type of sample studied.…”

“…18,26–28 This simple statement appears to overlook the complexity of singlet fission and triplet fusion that occurs in solid rubrene, dynamics that have been extensively studied in vapour-grown orthorhombic single crystals 31–45 and to a lesser degree in more complex thin films. 25,30,46–51…”

Near-infrared-to-visible upconversion from 980 nm excitation band by binary solid of PbS quantum dot with directly attached emitter

“…Compared to this, NIR-to-visible upconversion 21–40 still requires higher I th and shows lower UC-QY despite various strategies. Reports are very limited for the conversion from 800 nm or longer, which is an interesting region for photovoltaic devices, such as perovskite solar cells.…”