While organic electronics is mostly dominated by light-emitting diodes, photovoltaic cells and transistors, optoelectronics properties peculiar to organic semiconductors make them interesting candidates for the development of innovative and disruptive applications also in the field of light signal detection. In fact, organic-based photoactive media combine effective light absorption in the region of the spectrum from ultraviolet to near-infrared with good photogeneration yield and low-temperature processability over large areas and on virtually every substrate, which might enable innovative optoelectronic systems to be targeted for instance in the field of imaging, optical communications or biomedical sensing. In this review, after a brief resume of photogeneration basics and of devices operation mechanisms, we offer a broad overview of recent progress in the field, focusing on photodiodes and phototransistors. As to the former device category, very interesting values for figures of merit such as photoconversion efficiency, speed and minimum detectable signal level have been attained, and even though the simultaneous optimization of all these relevant parameters is demonstrated in a limited number of papers, real applications are within reach for this technology, as it is testified by the increasing number of realizations going beyond the single-device level and tackling more complex optoelectronic systems. As to phototransistors, a more recent subject of study in the framework of organic electronics, despite a broad distribution in the reported performances, best photoresponsivities outperform amorphous silicon-based devices. This suggests that organic phototransistors have a large potential to be used in a variety of optoelectronic peculiar applications, such as a photo-sensor, opto-isolator, image sensor, optically controlled phase shifter, and opto-electronic switch and memory.

Organic light detectors: photodiodes and phototransistors.

This short review surveys the development of red fluorescent materials for the application of organic light-emitting diodes (OLEDs) that generate red electroluminescence (EL). The merit and problems of current dopant-based, either fluorescent or phosphorescent, red OLEDs will be addressed first. Materials that offer unique EL characteristics, such as narrow and saturated red EL as well as current density or voltage-independent EL efficiency, are discussed. In addition to dopant-based and assist dopant-based red OLEDs for comparison purposes, the survey emphasizes nondoped red OLEDs that are fabricated with the newly emerging red fluorophores as the host-emitter. The advantage of host-emitting nondoped OLEDs compared with traditional dopant-based red OLEDs is described in view of the chemical and device structures of these materials.

Evolution of Red Organic Light-Emitting Diodes: Materials and Devices

Luminescent materials with efficient solid-state emissions are important for the advancement of optoelectronics. Recently, a new class of propeller-like luminogenic molecules with aggregation-induced emission (AIE) characteristics has drawn increasing research interest. Among them, tetraphenylethene (TPE) is an archetypal luminogen with a simple molecule structure but shows a splendid AIE effect. Utilizing TPE as a building block, an effective strategy to create efficient solid-state emitters is developed. In this feature article, we review mainly our recent work on the construction of luminogenic materials from TPE and present their applications in organic light-emitting diodes. The applicability of the synthetic strategy and the utility of the resulting materials are demonstrated.

Tetraphenylethene: a versatile AIE building block for the construction of efficient luminescent materials for organic light-emitting diodes

A new series of starburst triarylamine fluorophores SBCHO, DBCHO, CZCHO, CZCN, and SBCN, that incorporate diphenylamine or carbazole as the electron donor and dicyanovinyl or aldehyde as the electron acceptor, has been prepared and their photophysical properties are investigated. In sharp contrast to most red-emitting dopants, which show serious aggregation-caused quench phenomena, the new starburst triphenylamine derivatives reported here show unique enhanced emission in the solid state or upon aggregation. Organic light emitting diodes using these compounds as non-doped host emitters and hole transporters have been fabricated. The highest external quantum yield reaches 2.09 % for CZCHO. SBCHO was investigated as a chlorine gas fluorescence (FL) solid-film sensor for the first time. The high-intensity emission was ‘turned off' immediately after being blown by Cl2 gas.

Aggregation‐induced Emission (AIE)‐active Starburst Triarylamine Fluorophores as Potential Non‐doped Red Emitters for Organic Light‐emitting Diodes and Cl2 Gas Chemodosimeter

Organic light-emitting diodes (OLEDs) show great promise of revolutionizing display technologies in the scientific community. One successful approach for improved device efficiency has been to maximize the electron-hole recombination using dopants that emit from the triplet excited state. In this context, heavy transition metal complexes have recently gained tremendous academic and industrial research interest for fabricating highly efficient phosphorescent OLEDs by taking advantage of the 1:3 exciton singlet/triplet ratio predicted by simple spin statistics. Traditional room-temperature phosphorescent dyes are monofunctional materials working only as light-emitting centres but other key issues including charge generation and transport remain to be addressed in the electroluminescence. This Feature Article highlights recent and current advances in developing new synthetic strategies for multifunctional organometallic phosphors, which integrate both luminescent and charge carrier injection/transport functions into the same molecules so that they perform most, if not all, of the necessary functional roles (viz. photoexcitation, charge injection and transport as well as recombination) for achieving high-efficiency devices. Considerable focus is placed on the design concepts towards the tuning capability of charge-transport characteristics and phosphorescence emission colour of this prominent class of metallophosphors. In particular, the latest research endeavor in accomplishing novel triplet emitters with enhanced charge injection/charge transport of both hole and electron carriers is criticially discussed, which can provide good implications regarding their possible routes for future research development in the field.

/pdf/functional-metallophosphors-for-effective-charge-carrier-4m83pe2tkw.pdf

Functional metallophosphors for effective charge carrier injection/transport: New robust OLED materials with emerging applications

A new branched carbazole derivative, 1,3,5-tris(2-(9-ethylcarbazyl-3)ethylene)benzene (TECEB), was prepared as a hole-transporting material for organic light-emitting devices (OLEDs) TECEB is comparable to 1,4-bis(1-naphthylphenylamino)biphenyl (NPB) in terms of highest-occupied molecular orbital/lowest-unoccupied molecular orbial energy levels, hole-drift mobility, as well as device performance (maximum luminence of about 10 000 cd m-2 and current efficiency of 327 cd A-1) in a standard hole-transporting layer/tris-(8-hydroxyquinoline)aluminum double-layer device, but is superior to NPB in terms of its higher glass-transition temperature (Tg, 130 °C) and ease of synthesis The latter features suggest that TECEB can be a potential alternative material to NPB especially for high-temperature applications in OLEDs and other organic electronic devices

A High Tg Carbazole-Based Hole-Transporting Material for Organic Light-Emitting Devices

We report the synthesis of a novel starburst molecule, 4,4‘,4‘ ‘-tris(N-3-methylphenyl-N-(9-ethylcarbazyl-3)amino) triphenylamine (PCATA), and its application in organic light-emitting devices (OLEDs). The introduction of PCATA into the standard NPB/Alq3 OLED as the hole injecting and transporting layer dramatically enhanced the device efficiency to 5.7 cd/A and 2.2 lm/W, which are a factor of 2 higher than those of the standard OLED without the PCATA layer. The performance enhancement is attributed to a better balance of hole and electron injection in the PCATA-added OLED.

Novel Starburst Molecule as a Hole Injecting and Transporting Material for Organic Light-Emitting Devices

A new family of isophorone-based red fluorescent materials (A, B, C, and D) with a typical donor-π-acceptor structure was designed and synthesized for use in organic light-emitting devices (OLEDs)....

A new family of isophorone-based dopants for red organic electroluminescent devices

Enhancement of green electroluminescence from 2,5-di-p-anisyl-isobenzofuran by double-layer doping strategy

Organic photovoltaic devices using starburst amine PCATA as the electron donor layer gave a quantum efficiency of up to 21.7% at short-circuit conditions, which is higher than those reported for UV-sensitive organic PV cells.

Jiuyan Li

Papers

A High Tg Carbazole-Based Hole-Transporting Material for Organic Light-Emitting Devices

Novel Starburst Molecule as a Hole Injecting and Transporting Material for Organic Light-Emitting Devices

A new family of isophorone-based dopants for red organic electroluminescent devices

Enhancement of green electroluminescence from 2,5-di-p-anisyl-isobenzofuran by double-layer doping strategy

Efficient UV-sensitive organic photovoltaic devices using a starburst amine as electron donor