Abstract
Low-threshold, room-temperature polariton lasing is crucial for future application of polaritonic devices. Conjugated polymers are attractive candidates for room-temperature polariton lasers, due to their high exciton binding energy, very high oscillator strength, easy fabrication, and tunability. However, to date, polariton lasing has only been reported in one conjugated polymer, ladder-type MeLPPP, whose very rigid structure gives an atypically narrow excitonic linewidth. Here, we observe polariton lasing in a highly disordered prototypical conjugated polymer, poly(9,9-dioctylfluorene), thereby opening up the field of polymer materials for polaritonics. The long-range spatial coherence of the emission shows a maximum fringe visibility contrast of 72%. The observed polariton lasing threshold (27.7 μJ/cm2, corresponding to an absorbed pump fluence of 19.1 μJ/cm2) is an order of magnitude smaller than for the previous polymer polariton laser, potentially bringing electrical pumping of such devices a step closer.
Highlights
Strong coupling between an exciton transition and a resonant cavity mode results in a bosonic quasi-particle, known as a cavity polariton [1,2,3]
We show that the inhomogeneously broadened excitonic transition of the widely used poly(9,9-dioctylfluorene) (PFO) can strongly couple to the photon mode in a planar microcavity composed of distributed Bragg reflectors (DBRs) and exhibit evidence for low-threshold polariton lasing at room temperature based on a systematic characterization of the system [26,27,28]
The PFO thin films used in this study showed a high PL quantum yield (PLQY) of ∼50%
Summary
Strong coupling between an exciton transition and a resonant cavity mode results in a bosonic quasi-particle, known as a cavity polariton [1,2,3]. The single-particle Hamiltonian for this system has two new eigenstates—the lower and upper polariton branches (LPB and UPB). Polaritons scatter along the LPB to lower energy states and can eventually accumulate in the common ground state. Stimulated scattering into a macroscopically occupied state leads to coherent light emission which is defined as polariton lasing [4,5,6]. Population inversion is not necessary for polariton lasing [7], which can lead to significantly lower thresholds [8]
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