Date Published: November 08, 2018
Publisher: John Wiley and Sons Inc.
Author(s): Qi Zhang, Qi Wei, Xiangru Guo, Gang Hai, Huizhi Sun, Jiewei Li, Ruidong Xia, Yan Qian, Santiago Casado, José Raúl Castro‐Smirnov, Juan Cabanillas‐Gonzalez.
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.
Stock solutions of the materials in chloroform (15 mg mL−1 for F8BT, 25 mg mL−1 for the blue‐emitting oligomer hosts) were first obtained and subsequently mixed in the required ratios to obtain various blend solutions with different weight percentage of F8BT in hosts (1–60 wt% F8BT). Thin films for optical characterization (absorption, PL, PLQE) were prepared by spin‐coating (at speeds ranging from 1000 to 3500 rpm) blend solutions onto precleaned silica (Spectrosil B) substrates leading to films with 180–210 nm thicknesses.
The authors declare no conflict of interest.