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Solution-processed light-emitting device was feasibly achieved by a new exciplex-forming BCz3Ph : PO-T2T blend as the emitting layer casted on top of a thermally polymerized hole-transporting layer formed by a dicarbazole-based monomer BCzC4Sy.

Molecular design and precise control of thin-film morphology and crystallinity of solution-processed small molecules are important for enhancing charge transport mobility of organic field-effect transistors and gaining more insight into the structure-property relationship. Here, two donor-acceptor-donor (D-A-D) architecture small molecules

A new dioxasilepine and aryldiamine hybrid material

Two bipolar molecules CzT2.1 and CzT2.2 are examined as electron acceptors to form exciplexes with electron donors 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and 4,4’,4’’-tris(carbazol-9-yl)-triphenylamine (TCTA), respectively. The bipolar structural feature endows 1-(4-(9H-carbazol-9-yl)phenyl)-9-(4,6-diphenyl-1,3,5-triazin-2-yl)-9H-carbazole (CzT2.1) and 1-(4-(9H-carbazol-9-yl)phenyl)-9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9H-carbazole (CzT2.2) with hole- and electron-transporting properties, as well as the possibility of forming charge transfer emissive states. An aggregation-induced emission (AIE) protocol was employed to quickly screen the feasibility of exciplex formation of four donor (D):acceptor (A) blends as nanoparticles dispersed in tetrahydrofuran (THF) solution containing a high portion of water. Then, the vacuum-deposited D:A blended films were analyzed with steady and dynamic photophysical characterizations. The observed results indicate that the emissions of the D:A blends are contributed from the bipolar acceptor as well as the exciplex system. The proportion for each contribution relies on the exciplex formation efficiency and the intrinsic relaxation behavior of the bipolar acceptor. The D:A blends employing a stronger donor (TAPC) give a higher propensity of forming exciplexes as compared to those of counterparts with a weaker donor TCTA. The green device (EL λmax = 537 nm) with TAPC:CzT2.1 exciplex-forming blend as the emitting layer exhibits a high maximum external quantum efficiency (EQE) of 12.5% (39.2 cd A−1, 41.4 lm W−1) and limited efficiency roll-off (12.5%, 34.8 cd A−1, 39.1 lm W−1 at 100 cd m−2) owing to the fast decay lifetimes of the exciplex. The green exciplex-based device (EL λmax = 514 nm) adopting TAPC:CzT2.2 blend as the emitting layer offers an even higher EQE of 15.0% (45.7 cd A−1, 50.0 lm W−1), yet suffers a limited efficiency roll-off (14.3%, 43.6 cd A−1, 45.0 lm W−1 at 100 cd m−2) due to the prolonged decay lifetimes of the emissive components. This works highlights the use of emissive bipolar acceptors to create exciplex emission channels working together with the inherent acceptor emission for enhancing the organic light-emitting diode (OLED) device performance.

Two hexaphenylbenzene (HPB)-based donors (D), CzTT and DDT-HPB, are blended with the triazine-centered acceptors (A) CN-T2T and PO-T2T to examine exciplex formation.

The phosphor-converted light-emitting diode (PC-LED) has become an indispensable solid-state lighting and display technologies in the modern society. Nevertheless, the use of scarce rare-earth elements and the thermal quenching (TQ) behavior are still two most crucial issues yet to be solved. Here, this work successfully demonstrates a highly efficient and thermally stable green emissive MnI

This article describes the switchable fluorescence of a series of donor–acceptor type 2,2′-bipyridines. The original bipyridine molecules have four protonation sites – two on the amino donor sites and two on the pyridine acceptor cores. These nitrogen-containing sites are selectively protonated by suitable acids and the protonation influences the electronic conjugation and structure of the chromophores. Consequently, the emission characteristics of the molecules are affected, and this behaviour is reversible, i.e. the neutral original species are regenerated by the addition of an equivalent amount of base. The switchable behaviour of these compounds is accompanied by a visible colour change of the relevant solutions.

The most attractive aspect of perovskite nanocrystals (NCs) for optoelectronic applications is their widely tunable emission wavelength, but it has been quite challenging to tune it without sacrificing the photoluminescence quantum yield (PLQY). In this work, we report a facile ligand-optimized ion-exchange (LOIE) method to convert room-temperature spray-synthesized, perovskite parent NCs that emit a saturated green color to NCs capable of emitting colors across the entire visible spectrum. These NCs exhibited exceptionally stable and high PLQYs, particularly for the pure blue (96%) and red (93%) primary colors that are indispensable for display applications. Surprisingly, the blue- and red-emissive NCs obtained using the LOIE method preserved the cubic shape and cubic phase structure that they inherited from their parent NCs, while exhibiting high crystallinity and high color-purity. Together with the parent green-emissive NCs, the obtained blue- and red-emissive NCs provided a very wide color gamut, corresponding to a Digital Cinema Initiatives-P3 of 140% or an International Telecommunication Union Recommendation BT.2020 of 102%. With the superior optical merits of these LOIE-manipulated NCs, a corresponding color conversion luminescence device provided a high external quantum efficiency (10.5%) and extremely high brightness (970 000 cd/m2). This study provides a valid route toward highly stable, extremely emissive, and panchromatic perovskite NCs with potential use in a variety of future optoelectronic applications.

Three new carbazole-based hole-transporting materials PTCz-9′Cz, PTCz-3′TCz, and PTCz-NTol2 were synthesized, characterized, and examined for the propensity of exciplex formation with the electron-transporting material PO-T2T. Through enhancing the electron-donating ability of the substituents, the HOMO energy of the donors, PTCz-9′Cz, PTCz-3′TCz, and PTCz-NTol2, increased from −5.59 eV, −5.40 eV to −5.02 eV, respectively. Consequently, the photoluminescence of the corresponding exciplex is red-shifted, giving blue, green and orange emissions. Among these three donor : acceptor blends, the device utilizing PTCz-9′Cz : PO-T2T (2 : 1) as the emitting layer rendered the best device efficiency with a maximum external quantum efficiency (EQEmax) of 10.9%. Then, the two D–A–D-configurated fluorescent emitters, iCzPNT and iCzBTh2CN, with different electron-accepting cores were introduced as the emitting guests of this exciplex-forming cohost system to explore the possibility of high efficiency OLEDs with all organic materials. The device with 10 wt% iCzPNT as the dopant was found to give yellow electroluminescence (EL) (λEL= 578 nm and CIE (0.53, 0.46)) with an EQEmax of 7.8%, whereas the device with 10 wt% iCzBTh2CN as the dopant gave red EL (λEL = 618 nm and CIE (0.63, 0.37)) with an EQEmax of 8.0%. Thanks to the TADF feature of the exciplex-forming system, the energy transfer between the exciplex host and fluorescent guest proved to be a promising strategy to efficiently harvest the electro-generated singlet and triplet excitons for giving high efficiency OLED devices. This work highlights the versatility of introducing a substitution effect onto the electron donor to manipulate the emission wavelength of the exciplex and facilitate the identification of a good exciplex-forming system for serving as the cohost of tailor-made fluorescent emitters.

In this study, three different benzylammonium halide (Cl, Br, and I) salts were investigated to elucidate their effects as additives on MAPbI3 perovskite surface morphology, crystal structure, optical properties, and solar cell performance and stability. In particular, the additive benzylammonium chloride (BZACl) has a cationic benzylammonium (BZA) ion as a surface capping ligand and exhibits stronger electronegativity attributed to anionic Cl− ions for suppressing the defect formation of iodine vacancies. The study demonstrated that most effectively reducing the defects and suppressing non-radiative recombination result in a significant increase in the photoluminescence (PL) intensity and lifetime of BZACl-doped MAPbI3 thin films. By optimizing the concentration of BZACl to about 0.27 mol% relative to MAPbI3, the corresponding device exhibited a maximum power conversion efficiency (PCE) of 19.8%, with negligible hysteresis (PCE = 20.4% in reverse scan), in comparison with the PCE of 17.8% for the control device with pristine perovskite films. In addition, excellent moisture stability is demonstrated with 90% retainment of the initial efficiency after 30 days of unencapsulated operation under ambient air conditions (∼45% relative humidity). This work highlights the great potential of benzylammonium halide salts as additives for developing high-efficiency and simultaneously stable MAPbI3-based perovskite solar cells.

Donor–donor′–acceptor molecules where the donor′ bridges the donor and acceptor have different possible interaction pathways for charge transfer. Here we study a series of donor–donor′–acceptor molecules, having the same acceptor and donor′ but different donors, and donor′–phenyl spacer–acceptor to change the spatial separation and overlap between potential through-space donor–acceptor charge transfer (CT) in competition with donor′–acceptor through-bond CT. We determine that the charge transfer driving force plays a large role in dictating which charge transfer channel is favoured. Strong donors and acceptors with large driving force favour through-space CT. We also find that solid state host packing plays an important role, with small molecule hosts that pack tightly, distorting the guest molecules, reducing D–A separation to stabilise the through-space CT state over the through-bond state. Only the through-space CT states give fast reverse intersystem crossing and efficient TADF. These results give the first insight into the photophysics of through-space CT compared to through-bond states on the same molecule.

Effective multimodality phototheranostics under deep-penetration laser excitation is highly desired for tumor medicine, which is still at a deadlock due to lack of versatile photosensitizers with absorption located in the long-wavelength region. Herein, we demonstrate a stable organic photosensitizer nanoparticle based on molecular engineering of benzo[c]thiophene (BT)-based photoactivated molecules with strong wavelength-tunable absorption in the near-infrared region. Via molecular design, the absorption and singlet oxygen generation of BT molecules would be reliably tuned. Importantly, the nanoparticles with a red-shifted absorption peak of 843 nm not only show over 10-fold reactive oxygen species yield compared with indocyanine green but also demonstrate a notable photothermal effect and photoacoustic signal upon 808 nm excitation. The in vitro and in vivo experiments substantiate good multimodal anticancer efficacy and imaging performance of BT theranostics. This work provides an organic photosensitizer nanoparticle with long-wavelength excitation and high photoenergy conversion efficiency for multimodality phototherapy.

Four new donor-acceptor-acceptor' (D-A-A')-configured donors, CPNT, DCPNT, CPNBT, and DCPNBT equipped with naphtho[1,2-c:5,6-c']bis([1,2,5]-thiadiazole) (NT) or naphtho[2,3-c][1,2,5]thiadiazole (NBT) as the central acceptor (A) unit bridging triarylamine donor (D) and cyano or dicyanovinylene acceptor (A'), were synthesized and characterized. All molecules exhibit bathochromic absorption shifts as compared to those of the benzothiadiazole (BT)-based analogues owing to improved electron-withdrawing and quinoidal character of NT and NBT cores that lead to stronger intramolecular charge transfer. Favorable energy level alignments with C70 , together with the good thermal stability and the antiparallel dimeric packing render CPNT and DCPNT suitable donors for vacuum-processed organic photovoltaics (OPV)s. OPVs based on DCPNT : C70 active layers displayed the best power conversion efficiency (PCE)=8.3%, along with an open circuit voltage of 0.92 V, a short circuit current of 14.5 mA cm-2 and a fill factor of 62% under 1 sun intensity, simulated AM1.5G illumination. Importantly, continuous light-soaking with AM 1.5G illumination has verified the durability of the devices based on CPNT:C70 and DCPNT : C70 as the active blends. The devices were examined for their feasibility of indoor light harvesting under 500 lux illumination by a TLD-840 fluorescent lamp, giving PCE=12.8% and 12.6%, respectively. These results indicate that the NT-based D-A-A'-type donors CPNT and DCPNT are potential candidates for high-stability vacuum-processed OPVs suitable for indoor energy harvesting.

Herein, core-twisted tetrachloroperylenediimides (ClPDIs) were introduced as new efficient electron-transporting materials (ETMs) to replace the commonly used fullerene acceptor PC61 BM in inverted planar perovskite solar cells (PSCs). ClPDI showed a low-lying lowest unoccupied molecular orbital (LUMO) energy level of -3.95 eV, which was compatible with the conduction band of CH3 NH3 PbI3-x Clx (-3.90 eV). In addition, the role of the length of the alkyl side chain at the imide position of ClPDI in modulating the molecular solubility, aggregation capacity for charge-transport properties, surface hydrophobicity, and PSC performance was investigated. The device based on ClPDI-C4 (ClPDI with n-butyl side chains) as ETM achieved a maximum power conversion efficiency (PCE) of 17.3 % under standard AM 1.5G illumination, which iwas very competitive with that of the reference device employing PC61 BM/C60 (PCE=17.2 %) as ETM. Moreover, the devices with ClPDIs as ETMs exhibited better device stability than that with PC61 BM/C60 . This work highlights the great potential of ClPDI derivatives as low-cost (≈2.0 USD g-1 ) and effective ETMs to obtain efficient solution-processed inverted PSCs. This class of ClPDI derivatives is expected further promote the performance and stability of PSCs after extended investigation.

An efficient organic light-emitting diode based on the BCzPh:CN-T2T exciplex as an emitting layer (EML) has been fabricated by exploiting charge balance and favorable molecular orientations. To fur...

An acceptor-donor-acceptor (A-D-A)-type non-fullerene acceptor (NFA), PTTtID-Cl, featuring thieno[3,2-b]thieno[2''',3''':4'',5'']-pyrrolo[2'',3'':4',5']thieno[2',3':4,5]thieno-[2,3-d]pyrrole (DTPTt) as the electron-rich core and 2-(5,6-dichloro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (ID-Cl) as the peripheral electron-deficient terminal group was synthesized and characterized. PTTtID-Cl exhibited strong absorption in the range of 700-850 nm in CHCl3 and redshifted absorption centered at 881 nm in a thin film. The near infrared (NIR)-absorption of PTTtID-Cl was combined with a low-bandgap polymer donor (PTB7-Th) to achieve binary and semitransparent organic photovoltaics (OPVs) with a power conversion efficiency (PCE) of 8.9 % and 7.7 % (with an average visible transmittance (AVT) of 16.7 %), respectively. A ternary device with a ratio of PM7/PTTtID-Cl/IT-4F=1:0.15:0.85 (w/w) achieved a short-circuit current density of 19.46 mA cm-2 , an open-circuit voltage of 0.87 V, and a fill factor of 71.2 %, giving a PCE of 12.0 %. In addition, by employing the Ag/ITO/Ag microcavity structure, semitransparent colorful binary organic photovoltaics (OPVs) with superior transparency of 27.9 % at 427 nm and 22.7 % at 536 nm for blue and green devices, respectively, were prepared. The semitransparent colorful devices based on the optimized ternary blend gave PCEs of 8.7 %, 8.4 %, and 9.1 % for blue, green, and red devices, respectively. These results indicate the promising potential of PTTtID-Cl as a NIR-absorption NFA for applications in semitransparent colorful binary and ternary OPVs.

The development of optical organic nanoparticles (NPs) is desirable and widely studied. However, most organic chromophores are water-insoluble, and therefore, the derivatization and modification of these chromophores are difficult. Herein, we demonstrated a simple platform for the fabrication of organic nanoemitters by loading ten different organic dyes (molar masses of 479.1-1081.7 g/mol) into water-soluble polymer nanosponges composed of poly(styrene-alt-maleic acid) (PSMA). This nanolization strategy enables the incorporation of small commercial dyes (3.7–50% loading) and newly synthesized large photosensitive molecules (> 85% loading) into PSMA NPs and prevents the spontaneous aggregation of these hydrophobic chromophores in aqueous solutions. These low-cytotoxicity organic nanoparticles exhibited tunable red to near-infrared fluorescence emission for cellular imaging and biological tracking in vivo. Moreover, PSMA NPs loaded with designed NIR-photosensitive molecules were fabricated, and photodynamic therapy with these dye-loaded PSMA NPs for the photolysis of cancer cells was achieved when coupled with 808 nm laser excitation. Indeed, our work demonstrates a facile approach for increasing the biocompatibility and stability of organic dyes by loading them into water-soluble polymer-based carriers, providing a new perspective of organic optoelectronic materials in biomedical theranostic applications.

In recent years, the performance of perovskite quantum dots (QDs) and QD-based light-emitting diodes (QLEDs) has improved greatly, with electroluminescence (EL) efficiency of green and red emission exceeding 20%. However, the development of perovskite near-infrared (NIR) QLEDs has reached stagnation, where the reported maximum EL efficiency is still below 6%, limiting their further applications. In this work, new NIR-emissive FAPbI

Acridine-based donor-acceptor chromophores exhibiting E-type delayed fluorescence were substituted with bis-biuret H-bonding motifs to induce the formation of hollow spheres which can be deposited from solution to form the active component of OLED devices. In solution, the contribution of the delayed component is sensitive to disruption of the aggregates.

Spin flipping has recently been recognized as a critical mechanism to enable conversion from non-radiative triplets into radiative singlets, leading to thermally assisted delayed fluorescence (TADF) in organic light-emitting diodes (OLEDs). However, it is a controversial issue on how spin flipping is realized in the absence of heavy elements. This paper provides clear evidence to show that spin-orbital coupling (SOC) is indeed formed in charge-transfer (CT) states through donor–acceptor (D–A) design by using magneto-photoluminescence (magneto-PL), in both steady and dynamic states. Essentially, a magneto-PL signal is observed at a high field (up to 900 mT) only if the CT states are excited within D–A structures in a typical TADF emitter DMAC-TRZ in solutions. This provides unambiguous evidence to show the existence of SOC in TADF molecules where heavy elements are absent. An empirical model is proposed to show the SOC generated in CT states by considering orbital polarizations by optically induced dipoles (D+ → A−). Furthermore, SOC is confirmed to be responsible for realizing spin flipping by directly monitoring the delayed fluorescence while the density of non-radiative triplets is changed by oxygen molecules. More importantly, by using solvent polarity to change the dipole moment in CT states, it is revealed that SOC-induced spin flipping is largely changed, presenting a unified relationship between the SOC and the dipole moment to control the spin flipping enabling the conversion from non-radiative triplets into radiative singlets in TADF.

This paper demonstrates high-efficiency organic near-infrared (NIR) photodetection activity by increasing the symmetry of photoinduced charge density based on planar cyclic donor–acceptor structures. The record-high photosensing capability (gain: 3 × 105 and EQE: 43% at 3 V) is realized under NIR 780 nm illumination upon using the single-component active layer chloroaluminum phthalocyanine (ClAlPc) with planar cyclic intramolecular donor–acceptor structures to create four-fold symmetry of photoinduced charge density. Our in situ measurement using bias-dependent magneto-photocurrent reveals that increasing the symmetry of photoinduced charge density through planar cyclic intramolecular donor–acceptor structures can significantly decrease the electron–hole binding energies, allowing the direct generation of free photogenerated carriers without any heterojunction structures. Particularly, with the four-fold symmetry of photoinduced charge density, the dissociation of electron–hole pairs can be completed at an extremely low critical bias (24.8 mV) in the ClAlPc molecules. Such low critical bias provides the underlying mechanism to directly generate free carriers in the single-component active layer under NIR illumination. Clearly, by using planar cyclic intramolecular donor–acceptor structures, symmetrically arranging photoinduced charge density presents a fundamental strategy to develop high-efficiency NIR sensing capabilities with single-component active layer design in organic molecules.

International audience; A series of six compounds composed of an emissive oligofluorene or dithiophenethiobenzimidazole (p3) core bearing H-bonding biuret molecular recognition motifs in the meta-or para-position was investigated with regard to their propensity to undergo either social or narcissistic self-sorting when deposited from dilute THF solutions. The structural similarity of the compounds uniformly leads to social self-sorting with the exception of two combinations involving p3 for which narcissistic self-sorting is observed instead. Their behavior is attributed to the difference in location of the biuret groups (meta vs. para) combined with a greater structural difference in the conjugated core. Deposition of solutions demonstrating narcissistic self sorting gives rise to ensembles of disk-like aggregates exhibiting two different populations of emission (blue and magenta or yellow and orange).

Energy transfer between the exciplex host and fluorescent guest is a demanding process for attaining high-performance organic light-emitting diodes (OLEDs), particularly in the near-infrared (NIR) region, and insight into the dynamics of energy transfer has been elusive. In this study, new deep-red/NIR chromophores, NOz-TPA and NOz-t-TPA where NOz and TPA denote naphthobisoxadiazole and triphenylamine, respectively, have been developed with an electron donor–acceptor–donor (D–A–D) configuration. The optimized 1 wt% doped films for NOz-TPA and NOz-t-TPA blended with the Tris-PCz:CN-T2T (1 : 1 in molar ratio) exciplex host showed similar deep red/NIR emissions with photoluminescence quantum yields (PLQY) of 42 (680 nm) and 28%, (709 nm), respectively. Comprehensive time-resolved measurements and dynamics analyses revealed significant differences in the energy transfer pathways, i.e. Forster versus Dexter-type energy transfer between the exciplex host and the fluorescent guest, in which the introduction of bulky tert-butyl groups in the NOz-t-TPA doped film greatly suppressed the Dexter-type energy transfer pathway. Despite the lower PLQY, the analytical simulation predicted NOz-t-TPA to be a better candidate for realizing highly efficient electroluminescence. Confirmation was provided by the performance of the NOz-t-TPA-doped OLED, showing an external quantum efficiency (EQE) of 6.6% with peak wavelength at 710 nm, which is among the best records for the metal-free NIR OLEDs around 710 nm. Insight into energy transfer pathways thus plays a pivotal role in achieving the high-performance OLEDs that incorporate the exciplex host and fluorescent guest.

In this study, three triazatruxene-based molecules Tr-Me, Tr-Ph, and Tr-Tol with methyl, phenyl, and p-tolyl pendant groups, respectively, were intermixed with three acceptors 3P-T2T, 3P-T2P, and 3P-Pyr featuring phenylpyrazole peripherals and triazine, pyrimidine, and pyridine cores, respectively, to generate an array of nine blends to probe the feasibility of formation of an exciplex. The observed red-shifted emission compared to those of pristine donor and acceptor films is a good indication of exciplex formation. The exciplex emissions are mainly modulated by the features of N-heteroarene cores of acceptors, while the HOMOs of the donors are less influenced by the substituents. From the screening of these D:A combinations it was concluded that four exciplex-forming blends composed of Tr-Ph and Tr-Tol as donors and 3P-T2T and 3P-T2P as acceptors exhibit promising properties suitable for OLED applications. Among them, a green device employing a Tr-Tol:3P-T2P blend as the emitting layer performed with the best efficiency with a maximum external quantum efficiency (EQEmax) of up to 12.8%. These new exciplex-forming systems were further explored as cohosts for a newly developed fluorescent emitter (DT)2BTh2CN. The Tr-Ph:3P-T2P blend was found to serve as the best host to give a deep-red (EL λmax 671 nm, CIE (0.68, 0.31)) OLED device with an EQEmax of 5.52%. The data extracted from the transient photoluminescent studies shed light on the emission mechanism which is dominated by Forster energy transfer and simultaneously suffers from competing Dexter energy transfer quenching. Our results highlight the feasibility of using triazatruxene as the donor for exciplex formation as well as the tunability of the emission wavelength of exciplex-forming systems by rational structural modifications of both donors and acceptors.

A strategic approach combining a new co-host system and low concentration of new thermally activated delayed fluorescence (TADF) emitters to make efficient blue TADF organic light-emitting diode (OLED) was developed. The benchmark TADF molecule, 4CzIPN, was adopted as a probe to examine the feasibility of a co-host composing of a hole transporter SimCP and an electron transporter oCF3-T2T. As a result, a sky blue device with 1 wt % 4CzIPN doped in SimCP:oCF3-T2T co-host exhibited 100% energy transfer and achieved a high external quantum efficiency (EQE) up to 26.1%. Importantly, this device showed a limited efficiency rolloff with an EQE of 24% at 1000 cd m-2. To further shift the emission toward blue, three new TADF molecules, 4CzIPN-CF3, 3CzIPN-H-CF3, and 3CzIPN-CF3, modified either by lowering the electron-withdrawing ability of the acceptor group or by reducing the number of carbazole donors of 4CzIPN, have been synthesized and characterized. Among them, 4CzIPN-CF3 and 3CzIPN-H-CF3 display hypsochromic shift emissions compared to that of 4CzIPN. These new compounds were then explored for their potential applications as TADF emitters. Blue TADF OLEDs with 1 wt % of 4CzIPN-CF3 and 3CzIPN-H-CF3 dispersed in SimCP:oCF3-T2T co-host achieved EQEs of 23.1 and 16.5% and retained high EQEs of 20.9 and 14.7% at 1000 cd m-2, respectively.

Open circuit voltage of a photovoltaic system, in general, is constrained by the Schottky barrier (SB) heights formed at the electrodes. Here, the SB heights which are inhomogeneous in nature at the anode-semiconductor junction of a donor-acceptor-acceptor molecule, 2-[(7-(4-[N,N-bis(4-methylphenyl)amino]phenyl)-2,1,3-benzothia-diazol-4-yl)methylene] propane-dinitrile (DTDCPB), mixed with C70 as a bulk heterojunction have been studied thoroughly by inserting an insulating layer of MoO3 with different thicknesses (6 nm, 12 nm, 18 nm) and measuring the current density-voltage (J-V) and capacitance-voltage (C–V) characteristics of the photovoltaics under a large temperature range of 100K–300 K for proper estimation of open circuit voltage (Voc). Experimental results reveal a linear inverse temperature dependence of SB heights in the whole temperature range. The mismatch in the extracted values of SB heights from the independent measurements of J-V and C–V vanishes under the consideration of non-linear temperature dependence of built-in potential (Vbi) leading to the legitimate prediction of Voc.

We report on CdSe@ZnS light-emitting diodes (QLEDs) showing both high efficiency and long operational lifetime by introducing thermally cross-linkable 2,7-disubstituted fluorene-based triaryldiamine (VB-FNPD) as the hole transporting layer and 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN) as the hole injection layer. The green QLEDs achieved a maximum external quantum efficiency (EQE) of 8.0% and power efficiency (PE) of 32.1 lm W−1 with low efficiency roll-offs. More importantly, the corresponding QLED demonstrated a long lifespan in operation by simple encapsulation without desiccation. Under the initial luminance of 2000 cd m−2 and a continuous flow of constant current, the device still held luminance of 1000 cd m−2 after 50 h operation. The overall decay profile was fitted by two single exponential components, with time constants of 17.2 and ∼104 h, which is superior to that using the conventional polymer as the hole transporting layer. The thermally polymerizable hole transporting materials therefore offer an effective approach to realize both good efficiency and long-term stability in QLED.

The triad types of molecules with various combinations of electron donors (D) and acceptors (A) have been widely explored in optoelectronics. However, their photophysical and photochemical properti...

A series of bipolar host materials, namely, o-, m-, p-NPCz and o-, m-, p-NPDa, composing of electron-transporting naphthyridine (NP) and phenylene bridge with ortho-, meta-, and para-substituted hole-transporting carbazole (Cz)/diphenylamine (Da) were synthesized and characterized. By adjusting the linkage topology, the physical properties are subtly tuned. The characteristics of devices employing these new bipolar hosts with green thermally activated delayed fluorescence (TADF) emitter 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) employed as emitter were investigated under the same device structure. Among these hosts, carbazole-based NPCz can perform efficient energy transfer from the host to the dopant and better exciton confinement in the emitting layer due to higher triplet energy and deeper HOMO/LUMO level than those of diphenylamine-based NPDa. The device with o-NPCz as bipolar host exhibits the best device performance with external quantum efficiency of 18.4% and low efficiency roll-off. However, o-, m-, p-NPDa with lower ET and shallower HOMO levels than 4CzIPN exhibit inferior host to dopant energy transfer. Instead, the exciplex formation between host and 4CzIPN, which was verified by TRPL, led the resulting EL spectra of the NPDa-based devices broad with yellow to orange emissions.

Two new asymmetric D−π−A1−A2 configured small molecules named PTP and TTP bearing thieno[3,4-b]pyrazine (TP) unit as the A1 group have been designed and synthesized for solution-processed bulk-heterojunction organic solar cells (OSCs). These new dipolar molecular donors not only exhibit strong near-IR absorption but pack into antiparallel dimers, in which PTP shows a coexistence of coplanar and cofacial antiparallel dimers configuration, while TTP reveals a coplanar centrosymmetric dimer structure. Solution-processed OSCs for PTP blended with pristine C70 achieves a promising power conversion efficiency (PCE) of 3.40% along with an open-circuit voltage (VOC) of 0.64 V, a short-circuit current density (JSC) of 9.83 mA cm−2 and a fill factor (FF) of 54.0%, which is the highest efficiency to date among the TP-based materials. Conversely, the optimized TTP:C70 solar cell delivers a VOC of 0.48 V, a JSC of 6.02 mA cm−2 and a FF of 43.3%, corresponding to a moderate PCE of 1.25%.

Four new donor–acceptor–acceptor (D–A–A) type molecules (DTCPB, DTCTB, DTCPBO, and DTCTBO), wherein benzothiadiazole or benzoxadiazole serves as the central A bridging triarylamine (D) and cyano group (terminal A), have been synthesized and characterized. The intramolecular charge-transfer character renders these molecules with strong visible light absorption and forms antiparallel dimeric crystal packing with evident π–π intermolecular interactions. The characteristics of the vacuum-processed photovoltaic device with a bulk heterojunction active layer employing these molecules as electronic donors combining C70 as electronic acceptor were examined and a clear structure–property–performance relationship was concluded. Among them, the DTCPB-based device delivers the best power conversion efficiency (PCE) up to 6.55% under AM 1.5 G irradiation. The study of PCE dependence on the light intensity indicates the DTCPB-based device exhibits superior exciton dissociation and less propensity of geminated recombina...