Concurrent Optical Gain Optimization and Electrical Tuning in Novel Oligomer:Polymer Blends with Yellow‐Green Laser Emission

Abstract

Electrically pumped organic lasing requires the integration of electrodes contact into the laser cavity in an organic light‐emitting diode (OLED) or organic field effect transistor configuration to enable charge injection. Efficient and balanced carrier injection requires in turn alignment of the energy levels of the organic active layers with the Fermi levels of the cathode and anode. This can be achieved through chemical substitution with specific aromatic functional groups, although paying the price for a substantial (and often detrimental) change in the emission and light amplifying properties of the organic gain medium. Here, using host–guest energy transfer mixtures with hosts bearing a systematic and gradual shift in molecular orbitals is proposed, which reduces the amplified spontaneous emission (ASE) threshold of the organic gain medium significantly while leaving the peak emission unaffected. By virtue of the low guest doping required for complete host‐to‐guest energy transfer, the injection levels in the blends are attributed to the host whereas the gain properties solely depend on the guest. It is demonstrated that the ASE peak and thresholds of blends with different hosts do not differ while the current efficiency of OLEDs devices is deeply influenced by molecular orbital tuning of the hosts.

Azobenzene Sulphonic Dye Photoalignment as a Means to Fabricate Liquid Crystalline Conjugated Polymer Chain‐Orientation‐Based Optical Structures

“…We focus on the green‐light emission poly(9,9‐dioctylfluorene‐co‐benzothiadiazole) (F8BT) LCCP (Figure 1b) and a 90 wt% host:10 wt% guest binary blend with the red‐light emission complex copolymer Red F (comprising 9,9‐dioctylfluorene [50%], benzothiadiazole [40%], triarylamine [5%], and thiophene‐benzothiadiazole‐thiophene [5%] moieties; Figure 1c) as guest. F8BT has been widely deployed as the emission layer in polymer LEDs, as a laser gain medium23,38–40 and also as a resonance energy transfer host for red‐light emission guest gain polymers,41,42 including Red F 38,43–45. The large fractional overlap between the emission spectrum of F8BT and the absorption spectrum of Red F leads to efficient Förster energy transfer, resulting in red emission from the blend (vide infra).…”

Toward Electrically Pumped Organic Lasers: A Review and Outlook on Material Developments and Resonator Architectures

“…[13] Broad fluorescence spectra allow, on the other hand, for broadband amplification. [14,15] In addition, the photoluminescence (PL) spectra can be tailored by backbone modification, e.g., by controlling the conjugation length [16] or by the introduction of electron-donor or electron-acceptor groups, [17] in contrast to inorganic semiconductors where the emitting wavelengths are restricted to lattice-matching requirements. The efficiency of solid-state light emission is quantified through the photoluminescence quantum efficiency (PLQE), which stands for the ratio between the number of emitted and absorbed photons.…”

Organic Semiconductor Micro/Nanocrystals for Laser Applications

“…ASE does not require optical feedback because light amplification takes place by a single pass along the optical gain medium. ASE is typical of organic waveguides (slabs, 1D planar waveguides or optical fibers) [ 107 , 108 , 109 , 110 , 111 , 112 ] but can also be supported by organic crystals [ 68 , 113 , 114 ]. The ASE output is constituted by a spectrally broader emission linewidth (~10 nm) corresponding to the amplified waveguided mode along the crystal.…”