Polyarylamine-Based Polymeric Electret with Tunable Pendant Groups for Photorecoverable Organic Transistor Memory

Polyarylamine-based dielectric electrets and pentacene as p-type semiconductors have been utilized to fabricate photoresponsive flash transistor memories. In this study, three polyarylamines, PTTC (poly(5-(4-(diphenylamino)phenyl)thiophene-2-carbonitrile)), PTTP (poly(N,N-diphenyl-4-(5-phenylthiophen-2-yl)aniline)), and PDTPmC (poly(2-(5-(diphenylamino)thiophen-2-yl)pyrimidine-5-carbonitrile)), with different pendant moieties, have been synthesized and characterized. They have been investigated for their ability to trap holes and photorecovery behaviors. The PDTPmC electret, which features a high dipole moment, coplanar conformation, and highly conjugated structure, has demonstrated an outstanding hole-trapping capability with a memory window of 106 V and photorecoverability under light irradiation. The coplanar donor–acceptor configuration converging diphenylamine and thiophene-pyrimidine provides sufficient hole-trapping sites and delocalization ability for photoexcitation excitons. The PDTPmC-based memory device exhibits excellent switching reliability of electrical programming and optical erasing for 200 cycles, with a stable readout current ratio of approximately 105. This study proposes a polymer electret design approach to achieve high-performance transistor memory and photorecording device characteristics

Remote Steric Effect as a Facile Strategy for Improving the Efficiency of Exciplex-Based OLEDs

This work reports a new strategy of introducing remote steric effect onto the electron donor for giving the better performance of the exciplex-based organic light-emitting device (OLED). The bulky triphenylsilyl group (SiPh₃) was introduced onto the fluorene bridge of 4,4′-(9<i>H</i>-fluorene-9,9-diyl)­bis­(<i>N</i>,<i>N</i>-di-<i>p</i>-tolylaniline) (DTAF) to create remote steric interactions for increasing the possibility of effective contacts between electron-donating chromophores and acceptor molecules, rendering the resulting exciplex to have a higher photoluminescence quantum yield (PLQY). The green exciplex device based on DSDTAF:3N-T2T (1:1) as an emitting layer exhibits a low turn-on voltage of 2.0 V, high maximum efficiencies (13.2%, 42.9 cd A^–1, 45.5 lm W^–1), which are higher than the device employed DTAF (without SiPh₃ groups) (11.6%, 35.3 cd A^–1, 41.3 lm W^–1) as donor under the same device structure. This strategy was further examined for blue exciplex, where the EQE was enhanced from 9.5% to 12.5% as the electron acceptor PO-T2T mixed with a <i>tert</i>-butyl group substituted carbazole-based donor (CPTBF) as the emitting exciplex in device. This strategy is simple and useful for developing high performance exciplex OLEDs

Cyanopyrimidine–Carbazole Hybrid Host Materials for High-Efficiency and Low-Efficiency Roll-Off TADF OLEDs

Two isomeric host materials (<b>Sy</b> and <b>Asy</b>) comprising carbazole (donor) and CN-substituted pyrimidine (acceptor) were synthesized, characterized, and utilized as host materials for green and blue thermally activated delayed fluorescence (TADF) organic light emitting diodes (OLEDs). Both molecules have high triplet energy and small energy difference between singlet and triplet states, leading to feasible TADF. The different linking topologies of carbazole and CN groups on the pyrimidine core provide distinct photophysical properties and molecular packing manners, which further influence the efficiency as they served as hosts in TADF OLEDs. As compared to <b>Asy</b>-based cases, the <b>Sy</b>-hosted TADF OLED device gave higher maximum external quantum efficiencies (EQE) of 24.0% (vs 22.5%) for green (<b>4CzIPN</b> as a dopant) and 20.4% (vs 15.0%) for blue (<b>2CzTPN</b> as a dopant) and low efficiency roll-off. The high horizontal dipole ratio (Θ ≈ 88%) for both emitters dispersed in <b>Sy</b> and <b>Asy</b> hosts accounts for the high device efficiency. A clear molecular structure–physical property–device performance relationship has been established to highlight the importance of symmetrical structure in TADF host material design

Impact of Thermal Annealing on Organic Photovoltaic Cells Using Regioisomeric Donor–Acceptor–Acceptor Molecules

We report a promising set of donor–acceptor–acceptor (D–A–A) electron-donor materials based on coplanar thieno­[3,2-<i>b</i>]/[2,3-<i>b</i>]­indole, benzo­[<i>c</i>]­[1,2,5]­thiadiazole, and dicyanovinylene, which are found to show broadband absorption with high extinction coefficients. The role of the regioisomeric electron-donating thienoindole moiety on the physical and structural properties is examined. Bulk heterojunction (BHJ) organic photovoltaic cells (OPVs) based on the thieno­[2,3-<i>b</i>]­indole-based electron donor NTU-2, using C₇₀ as an electron acceptor, show a champion power conversion efficiency of 5.2% under AM 1.5G solar simulated illumination. This efficiency is limited by a low fill factor (FF), as has previously been the case in D–A–A systems. In order to identify the origin of the limited FF, further insight into donor layer charge-transport behavior is realized by examining planar heterojunction OPVs, with emphasis on the evolution of film morphology with thermal annealing. Compared to as-deposited OPVs that exhibit insufficient donor crystallinity, crystalline OPVs based on annealed thin films show an increase in the short-circuit current density, FF, and power conversion efficiency. These results suggest that that the crystallization of D–A–A molecules might not be realized spontaneously at room temperature and that further processing is needed to realize efficient charge transport in these materials

A Novel Amine-Free Dianchoring Organic Dye for Efficient Dye-Sensitized Solar Cells

An amine-free oligothiophene-based dye (<b>BTB</b>) featuring a tailor-made dianchoring function, a spiro-configured central unit, and bulky end-capping TIPS groups to diminish intermolecular interactions and to suppress aggregation-induced self-quenching was synthesized to achieve efficient dye-sensitized solar cells with a high power conversion efficiency of 6.52%

Highly Twisted Dianchoring D−π–A Sensitizers for Efficient Dye-Sensitized Solar Cells

Two new organic dyes<b>BPDTA</b> and <b>BTTA</b>possessing dual D−π–A units have been synthesized, characterized, and employed as efficient sensitizers for dye-sensitized solar cells. The two individual D−π–A, which are based on (E)-3-(5′-(4-(bis­(4-(hexyloxy)­phenyl)­amino)­phenyl)-[2,2′-bithiophen]-5-yl)-2-cyanoacrylic acid unit (<b>D21L6</b>), are connected directly between phenylene or thiophene within linear π-conjugated backbone to constitute a highly twisted architecture for suppressing the dye aggregation. The new dianchoring dyes exhibited pronounced absorption profile with higher molar extinction coefficient, which is consistent with the results obtained from density functional theory (DFT) calculations. The theoretical analysis also indicated that the charge transfer transition is mainly constituted of HOMO/HOMO–1 to LUMO/LUMO+1 that were found to be located on donor and acceptor segments, respectively. Theoretical calculations give the distance between two binding sites of 19.50 Å for <b>BPDTA</b> and 12.04 Å for <b>BTTA</b>. The proximity between two anchoring units of <b>BTTA</b> results in superior dye loading and, hence, higher cell efficiency. The <b>BTTA</b>-based device yielded an optimized efficiency of 6.86%, compared to 6.61% for the <b>BPDTA</b>-based device, whereas the model sensitizer <b>D21L6</b> only delivered an inferior performance of 5.33% under similar conditions. Our molecular design strategy thus opens up a new horizon to establish efficient dianchoring dyes

Indolo[2,3‑<i>b</i>]carbazole Synthesized from a Double-Intramolecular Buchwald–Hartwig Reaction: Its Application for a Dianchor DSSC Organic Dye

A new synthetic strategy for indolo­[2,3-<i>b</i>]­carbazole via a double-intramolecular Buchwald–Hartwig reaction has been established. The <i>N</i>-alkylated indolo­[2,3-<i>b</i>]­carbazole then was adopted as the geometry-fixed core for the synthesis of a new molecule (<b>ICZDTA</b>) bearing two bithiophene π-bridged 2-cyanoacrylic acid groups as the bidentate anchor. The bidentate anchoring together with efficient HOMO (indolo­[2,3-<i>b</i>]­carbazole) → LUMO (TiO₂ nanocluster) electron transfer leads to the successful development of <b>ICZDTA</b>-based DSSC with a power conversion efficiency of 6.02%

<i>S</i>,<i>N</i>‑Heteroacene-Based Copolymers for Highly Efficient Organic Field Effect Transistors and Organic Solar Cells: Critical Impact of Aromatic Subunits in the Ladder π‑System

Three novel donor–acceptor alternating polymers containing ladder-type pentacyclic heteroacenes (<b>PBo</b>, <b>PBi</b>, and <b>PT</b>) are synthesized, characterized, and further applied to organic field effect transistors (OFETs) and polymer solar cells. Significant aspects of quinoidal characters, electrochemical properties, optical absorption, frontier orbitals, backbone coplanarity, molecular orientation, charge carrier mobilities, morphology discrepancies, and the corresponding device performances are notably different with various heteroarenes. <b>PT</b> exhibits a stronger quinoidal mesomeric structure, linear and coplanar conformation, smooth surface morphology, and better bimodal crystalline structures, which is beneficial to extend the π-conjugation and promotes charge transport via 3-D transport pathways and in consequence improves overall device performances. Organic photovoltaics based on the <b>PT</b> polymer achieve a power conversion efficiency of 6.04% along with a high short-circuit current density (<i>J</i>_SC) of 14.68 mA cm^–2, and a high hole mobility of 0.1 cm² V^–1 s^–1 is fulfilled in an OFET, which is superior to those of its counterparts, <b>PBi</b> and <b>PBo</b>

Data_Sheet_1_Two Novel Small Molecule Donors and the Applications in Bulk-Heterojunction Solar Cells.DOC

<p>Two novel small molecules DTRDTQX and DTIDTQX, based on ditolylaminothienyl group as donor moiety and quinoxaline as middle acceptor moiety with different terminal acceptor groups were synthesized and characterized in this work. In order to study the photovoltaic properties of DTRDTQX and DTIDTQX, bulk-heterojunction solar cells with the configuration of FTO/c-TiO₂/DTRDTQX(or DTIDTQX):C₇₀/MoO₃/Ag were fabricated, in which DTRDTQX and DTIDTQX acted as the donors and neat C₇₀ as the acceptor. When the weight ratio of DTRDTQX:C₇₀ reached 1:2 and the active layer was annealed at 100°C, the optimal device was realized with the power conversion efficiency (PCE) of 1.44%. As to DTIDTQX:C₇₀-based devices, the highest PCE of 1.70% was achieved with the optimal blend ratio (DTIDTQX:C₇₀ = 1:2) and 100°C thermal annealing treatment. All the experimental data indicated that DTRDTQX and DTIDTQX could be employed as potential donor candidates for organic solar cell applications.</p

Balance the Carrier Mobility To Achieve High Performance Exciplex OLED Using a Triazine-Based Acceptor

A star-shaped 1,3,5-triazine/cyano hybrid molecule CN-T2T was designed and synthesized as a new electron acceptor for efficient exciplex-based OLED emitter by mixing with a suitable electron donor (Tris-PCz). The CN-T2T/Tris-PCz exciplex emission shows a high Φ_PL of 0.53 and a small Δ<i>E</i>_T‑S = −0.59 kcal/mol, affording intrinsically efficient fluorescence and highly efficient exciton up-conversion. The large energy level offsets between Tris-PCz and CN-T2T and the balanced hole and electron mobility of Tris-PCz and CN-T2T, respectively, ensuring sufficient carrier density accumulated in the interface for efficient generation of exciplex excitons. Employing a facile device structure composed as ITO/4% ReO₃:Tris-PCz (60 nm)/Tris-PCz (15 nm)/Tris-PCz:CN-T2T(1:1) (25 nm)/CN-T2T (50 nm)/Liq (0.5 nm)/Al (100 nm), in which the electron–hole capture is efficient without additional carrier injection barrier from donor (or acceptor) molecule and carriers mobilities are balanced in the emitting layer, leads to a highly efficient green exciplex OLED with external quantum efficiency (EQE) of 11.9%. The obtained EQE is 18% higher than that of a comparison device using an exciplex exhibiting a comparable Φ_PL (0.50), in which TCTA shows similar energy levels but higher hole mobility as compared with Tris-PCz. Our results clearly indicate the significance of mobility balance in governing the efficiency of exciplex-based OLED. Exploiting the Tris-PCz:CN-T2T exciplex as the host, we further demonstrated highly efficient yellow and red fluorescent OLEDs by doping 1 wt % Rubrene and DCJTB as emitter, achieving high EQE of 6.9 and 9.7%, respectively