Efficient Anisotropic Polariton Lasing Using Molecular Conformation and Orientation in Organic Microcavities

Abstract

Organic exciton-photon polariton lasers are promising candidates for the efficient generation of coherent light at room temperature. While their thresholds are now comparable with those of conventional organic photon lasers, tuning of molecular conformation and orientation as a means to control fundamental properties of their emission and thus further enhance performance remains largely unexplored. Here, a two-fold reduction in the threshold of a microcavity polariton laser based on an active layer of poly(9,9-dioctylfluorene) (PFO) is achieved when 15% β-phase conformation is introduced. In addtion, taking advantage of the liquid crystalline properties of PFO, a thin photoalignment layer is used to induce nematic alignment of the polymer chains. The resulting transition dipole moment orientation increases the Rabi energy, bringing the system into the ultra-strong coupling regime and facilitating anisotropic polariton lasing with an eight-fold reduction in absorbed threshold, down to 1.14 pJ (0.36 µJ cm −2 ) for the direction parallel to the orientation, with no emission along the orthogonal direction. This represents the first demonstration of anisotropic polariton lasing in conjugated polymer microcavities and a lower threshold than current organic vertical cavity surface-emitting photon and polariton lasers. Dipole orientation offers new opportunities for switchable, more efficient polaritonic devices, and observation of fundamental effects at low polariton numbers.

The Rise and Current Status of Polaritonic Photochemistry and Photophysics

“…The high penetration depth of the field into the reflectors reduces the available volume for molecules, reducing the average molecular density and thus the coupling strength. Another aspect is that the transition dipole moment and the vacuum electric field are vectors, which underlines the importance of their relative orientation. ,− …”

“…Another aspect is that the transition dipole moment and the vacuum electric field are vectors, which underlines the importance of their relative orientation. 30 , 70 − 72 …”

High-Brightness Blue Polariton Organic Light-Emitting Diodes

“…Under these conditions of strong light–matter coupling, hybridization of photons and excitons can lead to the formation of two new eigenstates called the upper and lower polariton . Strong coupling thus allows manipulation of the light and matter components of a system in new ways and therefore enables the design of devices with a number of interesting properties and with possible applications, e.g., in transistors, communication systems, and polariton lasers. − In addition, very recently, we have demonstrated that strong coupling and, in particular, the unique angular dispersion relation of polaritons can be used to generate angle independent emission with high color purity, which might have profound implications for the design of future displays . In order to be able to directly manipulate these systems using strong light–matter coupling, efficient polariton OLEDs must be developed.…”

Ultrastrong coupling in Super Yellow polymer microcavity and development of highly efficient polariton light-emitting diodes and light-emitting transistors

“…Since the first discovery of organic polaritons by Lidzey et al [1], many fascinating phenomena have been demonstrated in the strong coupling regime, such as high-temperature polariton condensation and superfluid transition [6][7][8][9], stimulated scattering [10], and optically pumped polariton lasing [11][12][13]. More recently, organic microcavities in the ultrastrong coupling regime (Rabi-splitting exceeds 20% of the exciton transition energy [14]) have been further achieved, bringing the prospect of non-classical physics and innovative device applications [15][16][17][18][19]. It is shown that strongly coupled materials are not specifically limited to the narrow-band absorbing molecules such as J-aggregate dyes [20,21].…”