Highly Substituted 10-RO-(hetero)acenes-Electric Properties of Vacuum-Deposited Molecular Films.

The functionalization of the aromatic backbone allows the improvement of the electrical properties of acene molecules in the amorphous layered structures of organic thin films. In the present work, we discuss the electric properties of the stable, amorphous, vacuum-deposited films prepared from five highly substituted 10-RO-acenes of various electronic properties, i.e., two extreme electron-donor (1,3-dioxa-cyclopenta[b]) anthracenes with all RO substituents, two anthracene carbaldehydes and one benzo[b]carbazole carbaldehyde possessing both electron-donor and acceptor substituents. The hole mobility data were obtained using subsequent steady state space charge limited currents (SCLC) and Time of Flight (TOF) measurements, performed on the same sample and these were then compared with the results of theoretical hole mobility calculations obtained using the Density Functional Theory (DFT) quantum-chemical calculations using the Marcus-Hush theory. The study shows a good agreement between the theoretical and experimental values which allows for the quick and quantitative estimation of Einstein's mobility values for highly substituted 10-RO anthracene and benzo[b]carbazole based on chemical calculations. This agreement also proves that the transport of holes follows the hopping mechanism. The theoretical calculations indicate that the reorganization energy plays a decisive role in the transport of holes in the amorphous layers of highly substituted hetero(acenes).

Generation of circular dichroism from superposed porphyrin films.

Circular dichroism (CD) was observed from the superposed porphyrin deposited glass plates, which were prepared by the vapor deposition of achiral porphyrin molecules and oriented to one direction by rubbing parallel to the surface of plate. The CD spectra depended on the twisted angle between the plates and the number of plates superposed. The observed CD spectra agreed with the simulated ones by the Mueller matrices superposition calculation using the observed linear dichroism spectra and linear birefringence spectra of each plate.

Managing Locally Excited and Charge-Transfer Triplet States to Facilitate Up-Conversion in Red TADF Emitters That Are Available for Both Vacuum- and Solution-Processes.

Developing red thermally activated delayed fluorescence (TADF) emitters for high-performance OLEDs is still facing great challenge. Herein, three red TADF emitters, pDBBPZ-DPXZ, pDTBPZ-DPXZ, and oDTBPZ-DPXZ, are designed and synthesized with same donor-acceptor (D-A) backbone with different peripheral groups attaching on the A moieties. Their lowest triplet states change from locally excited to charge transfer character leading to significantly enhance reverse intersystem crossing process. In particular, oDTBPZ-DPXZ exhibits efficient TADF feature and exciton utilization. It not only achieves an external quantum efficiency (EQE) of 20.1 % in red vacuum-processed OLED, but also realize a high EQE of 18.5 % in a solution-processed OLED, which is among the best results in solution-processed red TADF OLEDs. This work provides an effective strategy for designing red TADF molecules by managing energy level alignments to facilitate the up-conversion process and thus enhance exciton harvesting.

A New Dioxasilepine-Aryldiamine Hybrid Electron-Blocking Material for Wide Linear Dynamic Range and Fast Response Organic Photodetector.

A new dioxasilepine and aryldiamine hybrid material DPSi-DBDTA is designed to act as the electron-blocking layer (EBL) for vacuum-processed organic photodetector (OPD). The O-Si-O-linked cyclic structure leads DPSi-DBDTA to have dipolar character, high LUMO, and good thermal and morphology stability suitable for vacuum deposition. An initial trial with C60-based single active layer OPD device manifests the superior capability of DPSi-DBDTA for dark current suppression compared to the typical aryldiamines. Here, the bare and MoO3-doped DPSi-DBDTA is further examined as EBLs for the visible light responsive OPD comprising DTDCPB/C70 bulk heterojunction (BHJ) as the active layer. In sync with the result of C60-based OPD, the low dark current density and high specific detectivity D* (7.085 × 1012 cm Hz1/2 W-1) are achieved. The device with 5% MoO3-doped EBL can exhibit a wide linear dynamic range (LDR) up to 154.166 dB, which is attributed to suppression of both dark current density and carrier recombination. Additionally, the devices also manifest fast time-resolved performance in both frequency and transient response measurements. Especially for the device with 20% MoO3-doped EBL, a wide cutoff frequency response 692.047 kHz and record-high transient response demonstrating ≤0.683 µs for transient photovoltage (TPV) and ≤0.478 µs for transient photocurrent (TPC) have been realized, which is possibly owing to the balance of mobility that mitigates the damage from traps. Such submicrosecond response is comparable with the state-of-the-art perovskite-PDs and Si-PDs.

Vacuum-Deposited Blue Inorganic Perovskite Light-Emitting Diodes.

Perovskite light-emitting diodes (PeLEDs) have drawn great research attention because of their outstanding electroluminescence performance by solution processing. PeLEDs made by thermal evaporation are relatively rarely explored but are compatible to existing organic light-emitting diode industrial lines. Blue-emitting PeLEDs are all based on organic-containing perovskites, rather than more stable all-inorganic perovskites because of their poor solubility, too fast crystallization, uneven discrete films, and unattainable pure blue emission. Here, we report all-inorganic, vacuum-processed blue PeLEDs. High-throughput combinatorial approaches are employed to optimize Cs-Pb-Br-Cl composition in our dual-source co-evaporation system to achieve the balance between film photoluminescence and injection efficiency. The as-deposited perovskite films demonstrated excellent intrinsic stability against heat, UV-light, and humidity attack. A series of PeLEDs were obtained covering the standard blue spectral region with a best luminance of 121 cd/m2 and an external quantum efficiency of 0.38%. We believe that the vacuum processing strategy demonstrated here provides a very promising alternative way to produce efficient and stable all-inorganic blue-emitting PeLEDs.

High-Efficiency Phosphorescent Hybrid Organic-Inorganic Light-Emitting Diodes Using a Solution-Processed Small-Molecule Emissive Layer.

The morphology and optical and electrical properties of solution-processed and vacuum-deposited 4,4',4″-tris(carbazol-9-yl)triphenylamine (TCTA):2,2'-(1,3-phenylene)bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole] (OXD-7) composite films are investigated. All of the films exhibit smooth and pinhole-free morphology, while the evaporated films possess enhanced carrier-transport properties compared to solution-processed ones. The close correlation between the carrier-transport feature and the packing density of the film is established. High-efficiency monochromatic and white phosphorescent hybrid organic-inorganic light-emitting diodes with solution-processed small-molecule emissive layers are reported: the maximum external quantum efficiencies of blue, yellow, and red devices are 18.9, 14.6, and 10.2%, respectively; white devices show a maximum luminance efficiency of 40 cd A(-1) and a power efficiency of 20.8 lm W(-1) at 1000 cd m(-2). The efficiencies of blue, red, and white devices represent significant improvement over previously reported values.