arXiv subjects

Hassan A. Qureshi

Publications and source records attributed to Hassan A. Qureshi.

6 recordsLinked to original sources

arXiv2026

Nanoparticle Arrays for Efficient Organic Light-Emitting Diode Emission Management

OLEDs are increasingly applied in illumination and displays because they offer excellent color quality, are mechanically flexible, and are self-emissive. However, their usage is limited by low external quantum efficiency (EQE) and efficiency roll-off at high driving voltages. These limitations, together with demands for smaller pixels and device sizes in emerging technologies, motivate innovations that increase efficiency and allow replacing external optical elements with embedded solutions. Here, we demonstrate enhanced outcoupling as well as directional and polarization control of OLED emission, based on collective surface lattice resonances of plasmonic nanoparticle arrays that are embedded in the active layers of four different state-of-the-art OLED structures. Both square arrays and more complex lattices producing flat bands are demonstrated to guide the light to directions and polarizations determined by their optical modes. We show that by the design of the array geometry and the OLED structure, spectral and angular enhancement of the electroluminescence (EL), up to 30 %, can be achieved. Our results verify that surface lattice resonances of nanoparticle arrays offer a robust and versatile embedded solution for tailoring the OLED emission, as well as exciting prospects for efficiency increase if combined with narrow-spectrum emitters.

physics.optics↗

arXiv2026

A fully solution-processed organic microcavity laser in the strong light-matter coupling regime

Solid-state semiconductor lasers underpin technologies from telecommunications and data storage to sensing, medical diagnostics, and emerging quantum communication. Polaritons-hybrid exciton-photon states have further extended this reach, enabling room-temperature quantum effects such as low-threshold lasing and single-photon nonlinearities. Organic semiconductors are ideal for polaritonics due to their large exciton binding energy, strong optical nonlinearities, and straightforward processing, making them attractive for both classical and quantum photonics. While solution-processed organic films have been widely explored, their optical cavities have almost always been fabricated using vacuum deposition, limiting the realization of truly scalable and low-cost devices. Here, we report the first organic laser microcavities fabricated entirely by solution processing, which operate in the strong coupling regimeThe resulting platform can be driven reliably to high excitation densities, where we observe a reversible, interaction-driven redistribution of the polariton condensate, revealing a distinct polariton lasing behaviour in organic microcavities. Together, the fabrication approach and the observed lasing dynamics establish a route toward scalable polaritonic and quantum photonic technologies and provide new opportunities for studying nonlinear polariton physics in organic systems.

cond-mat.mtrl-sci↗

arXiv2024

Polaritons in non-fullerene acceptors for high responsivity angle-independent organic narrowband infrared photodiodes

Narrowband infrared organic photodetectors are in great demand for sensing, imaging, and spectroscopy applications. However, most existing strategies for narrowband detection depend on spectral filtering either through saturable absorption, which requires active layers exceeding 500 nm, restricting the choice of materials for producing high-quality films, or cavity effects, which inherently introduce strong angular dispersion. Microcavity exciton-polariton (polariton) modes, which emerge from strong exciton-photon coupling, have recently been explored as an angular dispersion suppression strategy for organic optoelectronics. In this work, we present the first narrowband infrared polariton organic photodiode that combines angle-independent response with a record-high responsivity of 0.24 A/W at 965 nm and -2 V. This device, featuring a 100-nm-thin active layer comprising a non-fullerene acceptor, exhibits a detection mode with a full-width at half maximum of less than 30 nm and a marginal angular dispersion of under 15 nm across $\pm$$45^\circ$. This study highlights the potential of polaritons as an innovative platform for developing next-generation optoelectronic devices that achieve simultaneous enhancements in optical and electronic performance.

physics.optics↗

arXiv2024

Giant Rabi splitting and polariton photoluminescence in an all solution-deposited dielectric microcavity

Planar microcavity polaritons have recently emerged as a promising technology for improving several performance characteristics of organic light-emitting diodes, photodiodes and photovoltaics. To form polaritons and achieve enhanced performance, traditional microcavities with high reflectivity mirrors are fabricated by energy-intensive physical vapor deposition methods, which restrict their use in applications requiring flexibility and low cost. Here, for the first time, we demonstrate a dielectric all-solution-processed polariton microcavity consisting of Rhodamine 6G films in a poly(vinyl alcohol) matrix, exhibiting more than 400 meV Rabi-splitting and photoluminescence with uniform dispersion along the lower polariton mode. Our fully automated deposition and annealing fabrication protocol played a key role in preventing interlayer mixing and producing high optical-quality polariton microcavities, enabling us to observe enhanced scattering of reservoir excitons to the lower polariton and to explore the effects of strong coupling on bimolecular interactions. Notably, we found that polariton microcavities exhibit a more than 10-fold increase in the critical excitation density for bimolecular annihilation compared to bare Rhodamine 6G films. This enhancement can only be partially attributed to the sub-3-fold measured enhancement in radiative lifetime, highlighting the critical role of strong coupling in the influence of molecular dynamics.

cond-mat.mtrl-sci↗

arXiv2023

Linear optical properties of organic microcavity polaritons with non-Markovian Quantum State Diffusion

Hybridisation of the cavity modes and the excitons to polariton states together with the coupling to the vibrational modes determine the linear optical properties of organic semiconductors in microcavities. In this article we compute the refractive index for such system using the Holstein-Tavis-Cummings model and determine then the linear optical properties using the transfer matrix method. We first extract the parameters for the exciton in our model from fitting to experimentally measured absorption of a 2,7-bis [9,9-di(4-methylphenyl)-fluoren-2-yl]-9,9-di(4-methylphenyl) fluorene (TDAF) molecular thin film. Then we compute the reflectivity of such a thin film in a metal clad microcavity system by including the dispersive microcavity mode to the model. We compute susceptibility of the model systems evolving just a single state vector by using the non-Markovian Quantum State Diffusion. The computed location and height of the lower and upper polaritons agree with the experiment within the estimated errorbars for small angles ($\leq 30^\circ$). For larger angles the location of the polariton resonances are within the estimated error.

quant-ph↗

arXiv2023

Identifying the origin of delayed electroluminescence in a polariton organic light-emitting diode

Modifying the energy landscape of existing molecular emitters is an attractive challenge with favourable outcomes in chemistry and organic optoelectronic research. It has recently been explored through strong light-matter coupling studies where the organic emitters were placed in an optical cavity. Nonetheless, a debate revolves around whether the observed change in the material properties represents novel coupled system dynamics or the unmasking of pre-existing material properties induced by light-matter interactions. Here, for the first time, we examined the effect of strong coupling in polariton organic light-emitting diodes via time-resolved electroluminescence studies. We accompanied our experimental analysis with theoretical fits using a model of coupled rate equations accounting for all major mechanisms that can result in delayed electroluminescence in organic emitters. We found that in our devices the delayed electroluminescence was dominated by emission from trapped charges and this mechanism remained unmodified in the presence of strong coupling.

cond-mat.mtrl-sci↗