Switching charge-transfer characteristics from p-type to n-type through molecular "doping" (co-crystallization)

A novel molecule, DTPTP, which originally is a p-type compound, can be switched to an n-type semiconductor through tetracyanoquinodimethane doping (co-crystallization).

Borrowing an idea from the silicon industry, where the charge-carrier's characteristics can be changed through heteroatom implantation, we believe that the charge transport nature of organic semiconductors can be switched through molecular “doping” (co-crystallization). Here, we report a novel molecule 2,7-di-tert-butyl-10,14-di(thiophen-2-yl)phenanthro[4,5-abc][1,2,5]thiadiazolo[3,4-i]phenazine (DTPTP), which originally is a p-type (0.3 cm² V^–1 s^–1) compound, and can be switched to an n-type semiconductor (DTPTP₂–TCNQ, 3 × 10^–3 cm² V^–1 s^–1 under air conditions) through tetracyanoquinodimethane (TCNQ) doping (co-crystallization). Single crystal X-ray studies revealed that TCNQ-doped DTPTP complexes (DTPTP₂–TCNQ) adopt a dense one-dimensional (1D) mixed π–π stacking mode with a ratio of DTPTP and TCNQ of 2 : 1, while pure DTPTP molecules utilize a herringbone-packing pattern. Interestingly, theoretical analysis suggested that there is a quasi-2D electron transport network in this host–guest system. Our research results might provide a new strategy, to switch the charge transport characteristics of an original system by appropriate molecular “doping” (co-crystal engineering).

Fusing N-heteroacene analogues into one "kinked" molecule with slipped two-dimensional ladder-like packing

An unexpected "kinked" N-heteroacene with a slipped two-dimensional ladder-like packing feature is produced from the conventional condensation reaction. The as-obtained compound [2,2']bi(5,12-bis(TIPS)piperazin-3-one[2,3-b]phenazine) (2BPP) consists of two identical backbones (5,12-bis(TIPS)piperazin-3-one[2,3-b]phenazine), which are fused together through a C[double bond, length as m-dash]C double bond and two intramolecular H-bonds. A study on the charge carrier transport indicates that a 2BPP single crystal has a hole mobility up to 0.3 cm2 V-1 s-1, while theoretical calculations suggest that this compound might possess potential well-balanced ambipolar charge-transport characteristics.

"Doping" pentacene with sp(2)-phosphorus atoms: towards high performance ambipolar semiconductors

Recent research progress in black phosphorus sheets strongly encourages us to employ pentacene as a parent system to systematically investigate how the "doping" of sp(2)-phosphorus atoms onto the backbone of pentacene influences its optical and charge transport properties. Our theoretical investigations proved that increasing the contribution of the pz atomic orbital of the sp(2)-phosphorus to the frontier molecular orbital of phosphapentacenes could significantly decrease both hole and electron reorganization energies and dramatically red-shift the absorption of pentacene. The record smallest hole and electron reorganization energies of 69.80 and 95.74 meV for heteropentacene derivatives were obtained. These results suggest that phosphapentacenes (or phosphaacenes) could be potential promising candidates to achieve both higher and balanced mobilities in organic field effect transistors and realize a better power conversion efficiency in organic photovoltaics.

A novel heteroacene 2-(perfluorophenyl)-1H-imidazo[4,5-b]phenazine for selective sensing of picric acid

A novel chemosensor probe (PFIPZ) has been successfully synthesized and can identify picric acid over other electron-deficient compounds or strong acids.

Enhancement of Performance and Mechanism Studies of All-Solution Processed Small-Molecule based Solar Cells with an Inverted Structure

Both solution-processed polymers and small molecule based solar cells have achieved PCEs over 9% with the conventional device structure. However, for the practical applications of photovoltaic technology, further enhancement of both device performance and stability are urgently required, particularly for the inverted structure devices, since this architecture will probably be most promising for the possible coming commercialization. In this work, we have fabricated both conventional and inverted structure devices using the same small molecular donor/acceptor materials and compared the performance of both device structures, and found that the inverted structure based device gave significantly improved performance, the highest PCE so far for inverted structure based device using small molecules as the donor. Furthermore, the inverted device shows a remarkable stability with almost no obvious degradation after three months. Systematic device physics and charge generation dynamics studies, including optical simulation, light-intensity-dependent current-voltage experiments, photocurrent density-effective voltage analyses, transient absorption measurements, and electrical simulations, indicate that the significantly enhanced performance using inverted device is ascribed to the increasing of Jsc compared to the conventional device, which in turn is mainly attributed to the increased absorption of photons in the active layers, rather than the reduced nongeminate recombination.

Paediatric CT dose: a multicentre audit of subspecialty practice in Australia and New Zealand

OBJECTIVES

To evaluate paediatric CT dosimetry in Australia and New Zealand and calculate size-specific dose estimates (SSDEs) for chest and abdominal examinations.

METHODS

Eight hospitals provided data from 12 CT systems for 1462 CTs in children aged 0-15. Imaging data were recorded for eight examinations: head (trauma, shunt), temporal bone, paranasal sinuses, chest (mass) and chest HRCT (high-resolution CT), and abdomen/pelvis (mass/inflammation). Dose data for cranial examinations were categorised by age and SSDEs by lateral dimension. Diagnostic reference ranges (DRRs) were defined by the 25th and 75th percentiles. Centralised image quality assessment was not undertaken.

RESULTS

DRRs for 201 abdominopelvic SSDEs were: 2.8-4.7, 3.6-11.5, 8.5-15.0, 7.6-15, and 10.6-16.2 for the <15 cm, 15-19 cm, 20-24 cm, 25-29 cm and >30 cm groups, respectively. For 147 chest examinations using these body width categories, SSDE DRRs were 2.0-4.4, 3.3-7.9, 4.0-9.4, 4.5-12, and 6.5-12. Kilovoltage peak (kVp), but not AEC or IR, was associated with SSDE (parameter estimate [standard error]: 0.12 (0.03); p < 0.0001).

CONCLUSIONS

Australian and New Zealand paediatric CT DRRs and abdominal SSDEs are comparable to international data. SSDEs for chest examinations are proposed. Dose variations could be reduced by adjusting kVp.

KEY POINTS

• SSDEs can be calculated for all patients, CT systems, and practices • Kilovoltage peak (kVp) has the greatest association with dose in similar-sized patients • Paediatric DRRs for CT are now available for use internationally.

A series of simple oligomer-like small molecules based on oligothiophenes for solution-processed solar cells with high efficiency

A series of acceptor-donor-acceptor simple oligomer-like small molecules based on oligothiophenes, namely, DRCN4T-DRCN9T, were designed and synthesized. Their optical, electrical, and thermal properties and photovoltaic performances were systematically investigated. Except for DRCN4T, excellent performances were obtained for DRCN5T-DRCN9T. The devices based on DRCN5T, DRCN7T, and DRCN9T with axisymmetric chemical structures exhibit much higher short-circuit current densities than those based on DRCN6T and DRCN8T with centrosymmetric chemical structures, which is attributed to their well-developed fibrillar network with a feature size less than 20 nm. The devices based on DRCN5T/PC71BM showed a notable certified power conversion efficiency (PCE) of 10.10% under AM 1.5G irradiation (100 mW cm(-2)) using a simple solution spin-coating fabrication process. This is the highest PCE for single-junction small-molecule-based organic photovoltaics (OPVs) reported to date. DRCN5T is a rather simpler molecule compared with all of the other high-performance molecules in OPVs to date, and this might highlight its advantage in the future possible commercialization of OPVs. These results demonstrate that a fine and balanced modification/design of chemical structure can make significant performance differences and that the performance of solution-processed small-molecule-based solar cells can be comparable to or even surpass that of their polymer counterparts.

Synthesis, structure, physical properties and OLED application of pyrazine–triphenylamine fused conjugated compounds

Several donor–acceptor compounds based on pyrazine–triphenylamine fused conjugated molecules have been fabricated in OLED devices. And the maximum EQE of 7.37% have been obtained.

Device characterization and optimization of small molecule organic solar cells assisted by modelling simulation of the current–voltage characteristics

A new equivalent electrical model was built in terms of semiconductor theory to simulate the current–voltage characteristics and reveal these current losses in solution processed small molecule based devices.

Impact of the electron-transport layer on the performance of solution-processed small-molecule organic solar cells

Although the performance of polymer solar cells has been improved significantly recently through careful optimization with different interlayers for the same materials, more improvement is needed in this respect for small-molecule-based solar cells, particularly for the electron-transport layers (ETLs). In this work, three different solution-processed ETLs, PFN, ZnO nanoparticles, and LiF, were investigated and compared in the performance of small-molecule-based devices, and power conversion efficiencies (PCEs) of 8.32, 7.30, and 7.38% were achieved, respectively. The mechanism for the ETL-induced enhancement has been studied, and different ETLs have a significantly different impact on the device performance. The clearly improved performance of PFN is attributed to the combination of reduced bimolecular recombination and increased effective photon absorption in the active layer.

Wearing a crotch strap on a correctly fitted lifejacket improves lifejacket performance

Wearing a lifejacket when immersed in water should support the wearer, maintaining their airway clear of the water. It is proposed that a retention system would improve airway protection by improving retention of the lifejacket around the torso. Study one (n = 10) quantified the performance of lifejackets immediately following a step into water from height when a lifejacket was worn with a crotch strap (two different tightness) and without a crotch strap. Airway freeboard was improved when wearing a crotch strap (P < 0.05) compared with no crotch strap. Study two used a manikin to examine the performance of lifejackets with and without a crotch strap during 3-h exposures to waves. During exposure to waves, the time taken to aspirate the lethal dose of seawater for drowning was doubled when wearing a crotch strap compared with the no-crotch-strap conditions (P < 0.001). Therefore, wearing a crotch strap (functioning retention system) on a correctly fitted lifejacket improves airway protection following accidental immersion and prolonged wave exposure.