We present a comprehensive study of transient nanosecond electroluminescence (EL) spikes that exceed the dc level and microseconds-long EL tails following a bias pulse in guest-host small molecular organic light-emitting diodes (SMOLEDs), including relatively efficient devices, which elucidates carrier and exciton dynamics in such devices. The transient EL is strongly dependent, among other parameters, on device materials and structure. At low temperatures, all measured devices, with the exception of Pt octaethylporphyrin (PtOEP)-doped tris(8-hydroxyquinoline) Al (Alq${}_3$) SMOLEDs, exhibit the spikes at ∼70–300 ns. At room temperature (RT), however, only those with a hole injection barrier, carrier-trapping guest-host emitting layer, and no strong electron-transporting and hole-blocking layer [such as 4,7-diphenyl-1,10-phenanthroline (BPhen)] exhibit strong spikes. These narrow and appear earlier under postpulse reverse bias. To further elucidate the origin of the spikes, we monitored their dependence on the pulsed bias width and voltage, the doped layer thickness, and its location within the OLED structure. The characteristics of the microseconds-long tails were also evaluated through the effect of the postpulse voltage. A model based on the recombination of correlated charge pairs (CCPs) and on charge detrapping is presented; the model agrees well with the experimental data. The results suggest that reduced electric-field-induced dissociative quenching of singlet excitons is responsible for the spikes’ amplitude exceeding the on-pulse dc EL level. The long tails are attributed to recombination of charges detrapped from a distribution of shallow, mostly host, sites, reminiscent of the detrapping and recombination processes that yield the thermally stimulated luminescence of such materials. The comprehensive transient EL measurements in guest-host devices demonstrate the generality of the strong spike phenomenon in devices with charge trapping in the emitting guest molecules. Hence the transient EL can serve as an important tool to identify the dominant emitting mechanisms in the guest-host systems.

Long-wavelength materials are key for development of pure-color and white organic light-emitting devices (OLEDs). An organic molecule, combining hybridized local electron and charge-transfer (HLCT) states and aggregation-induced emission (AIE), not only breaks the 5% external quantum efficiency (EQE) limit but also overcomes emission quenching. Herein, we designed and synthesized four novel donor–acceptor compounds of TBAN, TBT, TBAT, and TABAT using triphenylamine (TPA) as the donor, benzothiadiazole (BT) as the acceptor, and anthracene (AN) as a bridge. We found that the emission peaks of TBAN, TBT, TBAT and TABAT are located at 596, 615, 580 and 546 nm, respectively. We successfully applied them to non-doped OLEDs, and the resulting devices exhibited excellent performance. For example, the optimal TBAN-based OLEDs showed a maximum luminance of 74 820 cd m⁻², a current efficiency of 12.1 cd A⁻¹ and a maximum EQE of 5.7% with low roll-off. Additionally, the device with TBAN as both the emitter and hole-transport material also exhibited high efficiency that is comparable to that of an NPB-based device. This work demonstrates that it is feasible to obtain excellent orange and red emitters by employing BT- and TPA-based D–A architectures.

This review focuses on the utilization of organic photodetectors (OPDs) in optical analytical applications, highlighting examples of chemical and biological sensors and lab-on-a-chip spectrometers. The integration of OPDs with other organic optical sensor components, such as organic light emitting diode (OLED) excitation sources and thin organic sensing films, presents a step toward achieving compact, eventually disposable all-organic analytical devices. We discuss recent advances in developing and integrating OPDs for various applications as well as challenges faced in this area.