We report efficient tandem white organic light-emitting diodes (WOLEDs) by using bathocuproine:Cs2CO3∕MoO3 as an effective interconnecting layer. We utilized two primary colors of sky blue and orange fluorescent emitters to obtain efficient white electroluminescence. Although single WOLEDs using two adjacent emitting layers showed a maximum current efficiency of 7.96cd∕A with Commission Internationale d’Eclairage (CIE) coordinates of (0.28, 0.34), the tandem WOLED device made by stacking two single color OLEDs in series demonstrated doubled maximum current efficiency of 17.14cd∕A with CIE coordinates of (0.28, 0.41). The stacking of different single color OLEDs in series instead of double stacking of WOLEDs can be useful to achieve highly efficient WOLEDs because it can reduce the number of layers of the devices.

The authors report the very high luminous efficiency in solution processed red electrophosphorescent organic light emitting devices using small molecular host and guest materials. The maximum luminous efficiency reached 12.7cd∕A, corresponding to external quantum efficiency of 15.1%, with its emission peak wavelength of 620nm and the Commission Internationale de l’Eclairage coordinates of (0.65, 0.33). Along with these excellent performances of the solution processed device, which were comparable to those of the vacuum deposited counterpart device with similar structure and materials, the comparative study on both devices suggests the merits of the solution process adopting robust small molecular materials only.

We used a pulse-injection method to fix π-conjugated poly(3-hexylthiophene) (P3HT) molecules onto H-terminated Si(100) surfaces. Isolated molecules of P3HT were observed by scanning tunneling microscopy. The P3HT molecules comprised an almost all-trans conformation, reflecting the rigid feature of molecular chains. By quenching the substrate at 135 K, residual solvent molecules were observed. We could control the surface density of fixed P3HT molecules by changing both or either the volume or concentration of the injected P3HT solution.

Organic photodetectors (OPDs) exhibit superior spectral responses but slower photoresponse times compared to inorganic counterparts. Herein, we study the light-intensity-dependent OPD photoresponse time with two small-molecule donors (planar MPTA or twisted NP-SA) co-evaporated with C60 acceptors. MPTA:C60 exhibits the fastest response time at high-light intensities (>0.5 mW/cm2), attributed to its planar structure favoring strong intermolecular interactions. However, this blend exhibits the slowest response at low-light intensities, which is correlated with biphasic photocurrent transients indicative of the presence of a low density of deep trap states. Optical, structural, and energetical analyses indicate that MPTA molecular packing is strongly disrupted by C60, resulting in a larger (370 meV) HOMO level shift. This results in greater energetic inhomogeneity including possible MPTA-C60 adduct formation, leading to deep trap states which limit the low-light photoresponse time. This work provides important insights into the small molecule design rules critical for low charge-trapping and high-speed OPD applications.

The excellent contrast ratio, visibility, and advantages in producing thin and light displays let organic light emitting diodes change the paradigm of the display industry. To improve future display technologies, higher electroluminescence efficiency is needed. Herein, the detailed study of the non-radiative decay mechanism employing density functional theory calculations is carried out and a simple, general strategy for the design of the ancillary ligand is formulated. It is shown that steric bulk properly directed towards the phenylisoquinoline ligands can significantly reduce the non-radiative decay rate.