Abstract
Tetracene thin films are investigated by time-resolved photoluminescence on picosecond to nanosecond time-scales. The picosecond luminescence decay dynamics is confirmed to be independent of temperature, but the nanosecond timescale luminescence dynamics is highly temperature dependent. This is interpretted in terms of motion along an intermolecular coordinate which couples the S1 state to the multiexciton (ME) state, arising from frustrated photodimerization, and giving rise to exciton dimming through adiabatic coupling. Dull excitons persist at low temperatures, but can thermally access separated triplet states at higher temperatures, quenching the delayed fluorescence. The effects of exciton density on both the picosecond and nanosecond luminescence dynamics are investigated, and a rate constant of (1.70 ± 0.08) × 10(-8) cm(3) s(-1) is determined for singlet-singlet annihilation.
Highlights
Organic photovoltaics (OPV) are an emerging technology which have the potential to provide cheap and versatile solar energy conversion devices
The oscillator strength is shared between the two transitions and their relative contributions depend on the orientation of the crystallites
Considering the evidence, we agree that the energy of two separated triplets in tetracene is higher than the S1 state
Summary
Organic photovoltaics (OPV) are an emerging technology which have the potential to provide cheap and versatile solar energy conversion devices At present, these cells are far less efficient than their inorganic counterparts. One way to achieve a higher efficiency is by creating multiple excitons with high energy photons In organic materials this may be achieved by singlet fission, whereby an optically prepared singlet dissociates into two triplet excitons with (anti)-correlated spin The traps have variously been attributed to impurites,[36] and self-trapped excitons.[48] The exact nature remains unclear In this contribution, we reinvestigate the exciton dynamics of a tetracene thin film on time scales from 100 fs to 100 ns.
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