A unified picture of aggregate formation in a model polymer semiconductor during solution processing
Advanced Functional Materials Wiley (2024) 2314729
Abstract:
One grand challenge for printed organic electronics is the development of a knowledge platform that describes how polymer semiconductors assemble from solution, which requires a unified picture of the complex interplay of polymer solubility, mass transport, nucleation and, e.g., vitrification. One crucial aspect, thereby, is aggregate formation, i.e., the development of electronic coupling between adjacent chain segments. Here, it is shown that the critical aggregation temperatures in solution (no solvent evaporation allowed) and during film formation (solvent evaporation occurring) are excellent pointers to i) establish reliable criteria for polymer assembly into desired aggregates, and ii) advance mechanistic understanding of the overall polymer assembly. Indeed, important insights are provided on why aggregation occurs via a 1- or 2-step process depending on polymer solubility, deposition temperature and solvent evaporation rate; and the selection of deposition temperatures for specific scenarios (e.g., good vs bad solvent) is demystified. Collectively, it is demonstrated that relatively straightforward, concurrent in situ time-resolved absorbance and photoluminescence spectroscopies to monitor aggregate formation lead to highly useful and broadly applicable criteria for processing functional plastics. In turn, improved control over their properties and device performance can be obtained toward manufacturing sensors, energy-harvesting devices and, e.g., bioelectronics systems at high yield.Simple and Versatile Platforms for Manipulating Light with Matter: Strong Light-Matter Coupling in Fully Solution-Processed Optical Microcavities.
Advanced materials (Deerfield Beach, Fla.) (2023) e2212056
Abstract:
Planar microcavities with strong light-matter coupling, monolithically processed fully from solution, consisting of two polymer-based distributed Bragg reflectors (DBRs) comprising alternating layers of a high-refractive-index titanium oxide hydrate/poly(vinyl alcohol) hybrid material and a low-refractive-index fluorinated polymer are presented. The DBRs enclose a perylene diimide derivative (b-PDI-1) film positioned at the antinode of the optical mode. Strong light-matter coupling is achieved in these structures at the target excitation of the b-PDI-1. Indeed, the energy-dispersion relation (energy vs in-plane wavevector or output angle) in reflectance and the group delay of transmitted light in the microcavities show a clear anti-crossing-an energy gap between two distinct exciton-polariton dispersion branches. The agreement between classical electrodynamic simulations of the microcavity response and the experimental data demonstrates that the entire microcavity stack can be controllably produced as designed. Promisingly, the refractive index of the inorganic/organic hybrid layers used in the microcavity DBRs can be precisely manipulated between values of 1.50 to 2.10. Hence, microcavities with a wide spectral range of optical modes might be designed and produced with straightforward coating methodologies, enabling fine-tuning of the energy and lifetime of the microcavities' optical modes to harness strong light-matter coupling in a wide variety of solution processable active materials.Light regulation of organic light-emitting diodes with conductive distributed Bragg reflectors
Proceedings of SPIE - Volume 12314 - Optoelectronic Devices and Integration XI SPIE (2022)
Abstract:
Non-metallic mirror, such as semiconductor distributed Bragg reflectors (DBRs), has been widely integrated in the structure of optoelectronic devices. However, constructing conductive DBR in organic optoelectronic device is still scarce, because of the incompatibility of high-temperature processes in the preparation of inorganic DBR. Herein, it is confirmed that organic-oxide hybrid DBR can achieve high conductivity and light manipulation. When thermal evaporated material MoO3 is doped into organic material (1,1-bis[4-[N,N-di(p-tolyl)amino]phenyl]cyclohexane, TAPC), the conductivity of TAPC can be increased by ten thousand times with very small refractive index change. It is shown that 8.5 pairs DBR at 460 nm has a reflectivity of about 95%, and the driving voltage is 8.2 V at the current density of 100 mA cm-2. Then, a transparent organic light-emitting diode with integrated bottom conductive DBR are fabricated to confirm the functionality of light regulation. Our results confirm that integrated optoelectronic devices with DBR as reflector can be achieved with low operating voltage.Slow energy transfer in self-doped beta-conformation film of steric polydiarylfluorenes toward stable dual deep-blue amplified spontaneous emission
Advanced Optical Materials Wiley 10:1 (2021) 2100723
Abstract:
Exciton behavior is crucial for improving the optoelectronic property of a light-emitting conjugated polymer. Herein, the photoexcitation dynamics of exciton migration and energy transfer in a self-doped β-conformation film of the polydiarylfluorenes (poly[4-(octyloxy)-9,9-diphenylfluoren-2,7-diyl]-co-[5-(octyloxy)-9,9- diphenylfluoren-2,7-diyl], PODPF) are demonstrated. Compared to the first generation of the β-conformation polyfluorene, poly(9,9-dioctylfluorene) (PFO), energy transfer occurs in PODPF β-conformation films in a time period of ≈150 ps, much longer than those of the PFO ones (<5 ps), associated with the effective intrachain energy transfer (few hundred picoseconds), rather than interchain Förster energy transfer (a few picoseconds). Similar to PFO, the PODPF β-conformation also displays well-resolved vibronic emission peaks at 20 K, attributed to the planar and rigid conformation. Interestingly, a residual 0-0 band emission of nonplanar conformation chain segments (435 nm, 2.85 eV) at 20 K also further confirms the exciton migration from the amorphous state to the β-conformation domain in PODPF films. Therefore, the stable dual amplified spontaneous emission (ASE) behavior of the PODPF self-doped films at 461 nm (2.69 eV) and 483 nm (2.57 eV), originates from the individual amorphous and β-conformation domains.Planar refractive index patterning through microcontact photo-thermal annealing of a printable organic/inorganic hybrid material
Materials Horizons Royal Society of Chemistry 9:1 (2021) 411-416