Formation of electron traps in semiconducting polymers via a slow triple-encounter between trap precursor particles.

Already in 2012, Blom et al. reported (Nature Materials 2012, 11, 882) in semiconducting polymers on a general electron-trap density of ≈3 × 1017 cm-3, centered at an energy of ≈3.6 eV below vacuum. It was suggested that traps have an extrinsic origin, with the water-oxygen complex [2(H2O)-O2] as a possible candidate, based on its electron affinity. However, further evidence is lacking and the origin of universal electron traps remained elusive. Here, in polymer diodes, the temperature-dependence of reversible electron traps is investigated that develop under bias stress slowly over minutes to a density of 2 × 1017 cm-3, centered at an energy of 3.6 eV below vacuum. The trap build-up dynamics follows a 3rd-order kinetics, in line with that traps form via an encounter between three diffusing precursor particles. The accordance between universal and slowly evolving traps suggests that general electron traps in semiconducting polymers form via a triple-encounter process between oxygen and water molecules that form the suggested [2(H2O)-O2] complex as the trap origin.

Formation of universal electron traps in polymer light-emitting diodes is a dynamic process that occurs via a slow triple-encounter between trap precursor species, with the water-oxygen [2(H₂O)-O₂] complex as a likely candidate.

Shortwave infrared-absorbing squaraine dyes for all-organic optical upconversion devices.

Shortwave infrared (SWIR) optical sensing and imaging are essential to an increasing number of next-generation applications in communications, process control or medical imaging. An all-organic SWIR upconversion device (OUC) consists of an organic SWIR sensitive photodetector (PD) and an organic light-emitting diode (OLED), connected in series. OUCs directly convert SWIR to visible photons, which potentially provides a low-cost alternative to the current inorganic compound-based SWIR imaging technology. For OUC applications, only few organic materials have been reported with peak absorption past 1000 nm and simultaneous small absorption in the visible. Here, we synthesized a series of thermally stable high-extinction coefficient donor-substituted benz[cd]indole-capped SWIR squaraine dyes. First, we coupled the phenyl-, carbazole-, and thienyl-substituted benz[cd]indoles with squaric acid (to obtain the SQ dye family). We then combined these donors with the dicyanomethylene-substituted squaraine acceptor unit, to obtain the dicyanomethylene-functionalized squaraine DCSQ family. In the solid state, the absorbance of all dyes extended considerably beyond 1100 nm. For the carbazole- and thienyl-substituted DCSQ dyes, even the peak absorptions in solution were in the SWIR, at 1008 nm and 1014 nm. We fabricated DCSQ PDs with an external photon-to-current efficiency over 30%. We then combined the PD with a fluorescent OLED and fabricated long-term stable OUCs with peak sensitivity at 1020 nm, extending to beyond 1200 nm. Our OUCs are characterized by a very low dark luminance (<10-2 cd m-2 at below 6 V) in the absence of SWIR light, and a low turn-on voltage of 2 V when SWIR light is present.

Phosphorescent κ3 -(N

Efficient OLED devices have been fabricated using organometallic complexes of platinum group metals. Still, the high material cost and low stability represent central challenges for their application in commercial display technologies. Based on its innate stability, gold(III) complexes are emerging as promising candidates for high-performance OLEDs. Here, a series of alkynyl-, N-heterocyclic carbene (NHC)- and aryl-gold(III) complexes stabilized by a κ3 -(N^C^C) template have been prepared and their photophysical properties have been characterized in detail. These compounds exhibit good photoluminescence quantum efficiency (ηPL ) of up to 33 %. The PL emission can be tuned from sky-blue to yellowish green colors by variations on both the ancillary ligands as well as on the pincer template. Further, solution-processable OLED devices based on some of these complexes display remarkable emissive properties (ηCE 46.6 cd.A-1 and ηext 14.0 %), thus showcasing the potential of these motifs for the low-cost fabrication of display and illumination technologies.