Search

Multi-resonant thermally activated delayed fluorescent (MR-TADF) materials with boosting rate of Reverse Intersystem Crossing, subsequently alleviating External Quantum Efficiency roll off in OLEDs were discussed.

This work reveals the relationships between the ion species and charge collection, and enhances both the efficiency and stability of a PSC device.

The efficiency and device lifetime of quantum dot light-emitting diode (QLED) devices suffer from the charge imbalance issue resulting from excess electron injection from the ZnO electron transport layer (ETL) to the quantum dot (QD) emissive layer (EML). Herein we report 1,3-bis(9-phenyl-1,10-phenanthrolin-2-yl)benzene (BPPB) small molecule ETL blended ZnO as an interlayer in inverted red indium phosphide (InP) based QLEDs to slow down the ZnO ETL mobility. The device with ZnO : BPPB (15 wt%) shows 16.7% external quantum efficiency and 595 h lifetime (

A hole transporting type exciton blocking layer (hEBL) is one of the important device architecture components in phosphorescence organic light emitting diodes (PhOLEDs).

Procalcitonin (PCT) (i.e. a precursor of calcitonin) attracts much attention as a reliable biomarker of bacterial infections because its concentration increases rapidly in the blood when bacterial infections occur in the body. Sepsis may occur due to indiscriminate and vigorous proliferation of infectious bacteria, and accordingly early diagnosis and treatment of bacterial infection are of crucial importance. However, current diagnostic methods for sepsis suffer from long assay time, multiple and complex assay steps, inaccuracy, and requirement of analytical equipments. The goal of this study is to develop an advanced one-step-immunoassay that enables quick and accurate diagnosis of sepsis through measuring the PCT concentration in patient sera, which is based on self-enhancement of optical detection signals from large gold particles (i.e. clusters of gold nanoparticles) that are formed on the agglomerates of PCT-bound 3-dimensional (3D) probes. The 3D probe is constructed through attaching polyclonal anti-PCT antibodies (IgGs) to the surface of a modified hepatitis B virus (HBV) capsid, where both tandem repeats of the B domain of Staphylococcal protein A (SPAB) and the hexa-histidine tag are inserted into each HBV core protein (i.e. subunit of HBV capsid). That is, anti-PCT IgGs are attached via strong interaction between the Fc region and surface-exposed SPAB. Furthermore, hook effect-free and PCT concentration-dependent optical signals were consistently generated by adding both bovine serum albumin (BSA) and nickel ions to patient sera and also by optimally adjusting the 3D probe concentration. Compared to conventional chemiluminescent microparticle immunoassay (CMIA) showing poor linearity of detection signals, this novel immunoassay accurately detected PCT with good linearity between PCT concentrations and optical signals in a wide range of PCT concentrations (0.05–200 ng mL−1) and also showed a sufficiently low limit of detection, resulting in 100% sensitivity and 100% specificity when tested with 30 sepsis patients and 30 healthy individuals.

Two novel, CN-substituted ortho-terphenyl (OTP) core based bipolar type host materials were designed and synthesized for application in blue thermally activated delayed fluorescence (TADF) devices. Both hosts, 3,3′′-di(9H-carbazol-9-yl)-[1,1′:2′,1′′-terphenyl]-3′-carbonitrile (oCN-OTP) and 3,3′′-di(9H-carbazol-9-yl)-[1,1′:2′,1′′-terphenyl]-4′-carbonitrile (mCN-OTP) with a CN moiety substituted on the ortho- and meta-position of the terphenyl core brought an impressive result in photophysical properties and charge carrier transporting ability. Moreover, the introduction of the CN moiety over the ortho-terphenyl core which connected with carbazole donor units not only enables achieving high triplet energy level but also enhances the bipolar characteristics. As expected, our new design strategy leads to enhancing the device efficiencies when employed with a stable blue TADF dopant of 5-(5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)-10,15-diphenyl-10,15-dihydro-5H diindolo [3,2-a:3′,2′-c]carbazole (DBA-DI). The device with oCN-OTP as a host material (30% DBA-DI) exhibited excellent current and external quantum efficiencies of 58.2 cd A−1 and 29.5%, respectively. Interestingly, the oCN-OTP based blue TADF device recorded a longer device lifetime (LT90) of 28.8 hours at an initial luminance of 1000 cd m−2.

Efficient and selective production of CH4 through the CO2 reduction reaction (CO2RR) is a challenging task due to the high amount of energy consumption and various reaction pathways. Here, we report the synthesis of Zn-based polyoxometalate (ZnPOM) and its application in the photocatalytic CO2RR. Unlike conventional Zn-based catalysts that produce CO, ZnPOM can selectively catalyze the production of CH4 in the presence of an Ir-based photosensitizer (TIr3) through the photocatalytic CO2RR. Photophysical and computation analyses suggest that selective photocatalytic production of CH4 using ZnPOM and TIr3 can be attributed to (1) the exceptionally fast transfer of photogenerated electrons from TIr3 to ZnPOM through the strong molecular interactions between them and (2) effective transfer of electrons from ZnPOM to *CO intermediates due to significant hybridization of their molecular orbitals. This study provides insights into the design of novel CO2RR catalysts for CH4 production beyond the limitations in conventional studies that focus on Cu-based materials.

Two bipolar host materials were designed and synthesized for blue thermally activated delayed fluorescence (TADF) OLEDs. Both bipolar materials, 5-(4-(dibenzo[b,d]furan-2-yl)-pyridin-2-yl)-5H-benzo[d]benzo-[4,5]imidazo[1,2-a]imidazole (4-DBFBI) and 5-(5-(dibenzo[b,d]furan-2-yl)-pyridin-2-yl)-5H-benzo[d]benzo-[4,5]imidazo[1,2-a]imidazole (5-DBFBI), were constructed with a hole-transporting type of benzimidazole moiety and an electron-transporting type of dibenzofuran moiety, and these derivatives exhibit high triplet energy over 3.10 eV. To achieve a high triplet energy level, a pyridine linker was placed between the benzimidazole and dibenzofuran moieties. As a result, 4-DBFBI and 5-DBFBI showed a high triplet energy level of 3.06 eV and 2.96 eV, respectively. Further, blue TADF devices were fabricated with our synthesized bipolar host materials. For our current study, we adopted 5,10-diphenyl-15-(10-(2,4,6-triisopropylphenyl)-10H-dibenzo[b,e][1,4]oxaborinin-3-yl)-10,15-dihydro-5H-diindolo[3,2-a:3′,2′-c]carbazole (PXB-DI) as the blue TADF dopant. The maximum external quantum efficiencies of the 20 wt% blue TADF devices were 31.8 and 32.5% for 4-DBFBI and 5-DBFBI, respectively. Moreover, the 4-DBFBI based host device exhibited a very low efficiency roll-off of 0.93 up to 1000 cd m−2, which is attributed to its well-balanced charge transporting ability.

Photo-rechargeable batteries (PRBs) benefit from their bifunctionality covering energy harvesting and storage. However, dim-light performances of the PRBs for indoor applications have not been reported. Herein, we present an external-power-free single-structured PRB named a dye-sensitized photo-rechargeable battery (DSPB) with an outstanding light-to-charge energy efficiency (ηoverall) of 11.5% under the dim light condition. This unprecedented ηoverall was attributed to the thermodynamically-favorable design of the DSPB that maximizes the working potential. At high-power irradiation, the kinetically-fast but thermodynamically-unfavorable iodine mediator (I−/I3−) showed the highest charge and discharge capacities even if its discharge voltage was lowest. Under dim-light for indoor applications, however, the thermodynamically-favorable but kinetically-slow copper complex mediator (Cu+/2+(dmp)2) showed energy density and efficiency superior to I−/I3− because its kinetics did not limit the harvesting capacity. The successful demonstration of the ability of the DSPB to operate a temperature-sensing IoT device only by indoor light opens the possibility of realizing indoor-light-harvesting PRBs.

We’ve observed intense fluorescence from the surface of lead formate crystals when they are precipitated from a CH3NH3PbBr3 (MAPbBr3) perovskite precursor solution. The crystals exhibit emission in the range of 500–550 nm with a photoluminescence quantum yield (PLQY) of up to 70%. The fluorescence is stable in water and at elevated temperature without significant decrease in PLQY for months, conditions which instantly decompose MAPbBr3. Fluorescence occurred with the highest quantum efficiency of 70% at an optimal 1 : 0.3 molar ratio of methylammonium formate and lead bromide and decreased rapidly for other ratios. Fluorescence was quenched using other halides (Cl or I) or other cations (Cs, ethylammonium, propylammonium, etc.). Single crystal analysis indicates that the material possesses the lead formate structure with lattice parameters which are identical to pristine lead formate, however, analysis of the particles by EDX, XPS and fluorescence microscopy confirms the presence of Br and fluorescence emission on the particle surfaces. The observed material characteristics indicate that the emissive species consists of a mixed-valence surface layer of Pb coordinated to both Br and formate ligands.

Two new blue TADF emitters, namely, 9′-(2,12-di-tert-butyl-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)-9,9′′-diphenyl-9H,9′H,9′′H-3,3′:6′,3′′-tercarbazole (3CzTB) and 9′-(5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracen-7-yl)-6,6′′-dimethyl-9,9′′-diphenyl-9H,9′H,9′′H-3,3′:6′,3′′-tercarbazole (M3CzB), for application in highly efficient organic light-emitting diodes are reported. These emitters consist of tercarbazole as donor and rigid oxygen bridged boron as acceptor units. Despite having the same donor and acceptor segments, an alkyl modification on the periphery of the donor and acceptor units altered their physicochemical properties and the electrochemical stability of the emitters. Blue TADF light-emitting devices fabricated with these emitters exhibited a maximum external quantum efficiency (EQE) and luminance of 30.7%, 18 160 cd m−2 and 29.1%, 11 690 cd m−2 for M3CzB and 3CzTB, respectively. The operational lifetime (LT50) of the stable blue TADF device fabricated with these emitters was 81 h and 60.5 h at 400 nits with the maximum EQE and CIE color coordinates of 14.4%, (0.13, 0.19) and 7.6%, (0.14, 0.10) for M3CzB and 3CzTB, respectively.

In this study, we report an accurate and more reliable approach to estimate the dipole orientation of emitters especially phosphorescence, fluorescence and even thermally activated delayed fluorescence. The dipole orientation measurements are performed by examining the variation of the photoluminescence (PL) exciton decay rate from time-resolved PL and optical analysis. Our anisotropic dipole orientation results are consistent with those of previous reports. The studied measurement approach is very reliable and accurate to estimate the dipole orientation of any organic semiconductor materials regardless of whether they are doped or neat films.

Two thermally activated delayed fluorescence (TADF) emitters with high synthetic yields were designed and synthesized. Both emitters, 10,10′-(5-(4,6-diphenyl-1,3,5-triazin-2-yl)-1,3-phenylene)bis(9,9-dimethyl-9,10-dihydroacridine) (TRZ-DDMAc) and 10,10′-(5-(4,6-diphenyl-1,3,5-triazin-2-yl)-1,3-phenylene)bis(9,9-diphenyl-9,10-dihydroacridine) (TRZ-DDPAc), showed excellent photophysical properties. Interestingly, both of the materials had a small energy difference between singlet and triplet levels, which confirmed that donor–acceptor based molecular design brought effective reverse intersystem crossing (RISC) to enable the TADF mechanism. The TADF characteristic was confirmed by a delay time of 10.32 and 10.37 μs for TRZ-DDMAc and TRZ-DDPAc, respectively. TRZ-DDPAc revealed a photoluminescence quantum yield of 79.7% in a doped film state. Moreover, several green OLED devices were fabricated by using different host materials along with various doping concentrations to ensure the optimal performance of each TADF material. The device with TRZ-DDPAc as an emitter (30%: DBFPO) exhibited excellent current and maximum external quantum efficiencies of 62.8 cd A−1 and 27.3%, respectively. Green colour emission was observed from all devices, which originated through the TADF mechanism.

In this communication, we report an excellent new highly conjugated and rigid electron donor (diindolocarbazole) for thermally activated delayed fluorescence (TADF) emitters. The donor–acceptor structure with diindolocarbazole donor induces high oscillator strength as well as high probability for the radiative transition, suitable frontier molecular overlap with proper intramolecular charge transfer and a large dihedral angle with out-of-plane structure between electron donor and acceptor; this results in high photoluminescence quantum yield, small singlet–triplet energy splitting, and extremely short delayed fluorescence exciton lifetime. The fabricated organic light emitting diode with new donor applied green emitter exhibits a remarkably high external quantum efficiency of 31.4% without any out-coupling technique. It also shows extremely low efficiency roll-off characteristics with the highest luminance of 71 160 cd m−2 as well as good operational device stability.

New versatile host materials with good solubility in common organic solvents are greatly desired to promote solution-processable thermally activated delayed fluorescence organic light-emitting diodes. This paper describes the design and synthesis of two new host materials, namely 3′-(9H-carbazol-9-yl)-[1,1′-biphenyl]-3,5-diylbis(diphenylphosphine oxide) (CDPO) and 3′,5′-di-(9H-carbazol-9-yl)-[1,1′-biphenyl]-3,5-diylbis (diphenylphosphine oxide) (mCPDPO), featuring hole-transporting carbazole and electron-transporting diphenylphosphine oxide (DPO) entities. The donor strength was varied to a constant n-type DPO core to tune the functional properties. The detailed studies proved that the resulting two new materials exhibit excellent solubility in common organic solvents, high triplet energy (>2.80 eV), high glass transition temperature (up to 133 °C), and good bipolar electronic nature. Consequently, both compounds were used as hosts in solution-processable blue and green thermally activated delayed fluorescence (TADF) OLEDs. In particular, the devices using mCPDPO as a host in the emissive layer showed outstanding performance with a maximum current efficiency, power efficiency, and external quantum efficiency of 35.3 cd A−1, 17.0 lm W−1 and 15.4% in the blue-emitting diode, and 61.5 cd A−1, 29.7 lm W−1 and 18.8% in the green-emitting diode, respectively. These results corroborated the potential of carbazole-phosphine oxide derivatives as host materials in solution-processable blue and green TADF OLEDs.

Two bipolar host materials, 8-(9H-carbazol-9-yl)-5-(pyridin-2-yl)-5H-pyrido[3,2-b]indole (CzCbPy) and 5-(6-(9H-carbazol-9-yl)pyridin-2-yl)-8-(9H-carbazol-9-yl)-5H-pyrido[3,2-b]indole (2CzCbPy), were synthesized for deep blue thermally activated delayed fluorescence organic light emitting diodes (TADF OLEDs). Both CzCbPy and 2CzCbPy hosts possess bipolar characteristic with high polarity, which results in high delayed photoluminescence quantum yields by reducing the energy gap between singlet and triplet states of TADF materials. In addition, these hosts have high enough triplet energies of 3.05 eV to transfer exciton energy to a deep blue TADF emitter. A deep blue TADF OLED fabricated with a CzCbPy host exhibited high external quantum efficiency of 22.9% and low efficiency roll-off (19.2% at 1000 cd m−2).

Solution-processable thermally activated delayed fluorescence (TADF)-assisted materials have been identified as promising materials for future applications as organic light-emitting diodes (OLEDs) owing to their numerous advantageous such as easy fabrication, large area applications, low cost, and state-of-the-art performance. Herein, two new carbazole-dendronized TADF emitters, namely, TB2CZ-ACTRZ and TB14CZ-ACTRZ, were designed and synthesized. Two different-sized carbazole dendron wedges were utilized as the encapsulating groups for the TADF core via methylene groups. The influence of the encapsulated dendrons on the thermal, optical, electrochemical, and OLED device performances of both dendritic molecules was studied in detail. The photophysical studies of TB2CZ-ACTRZ and TB14CZ-ACTRZ disclosed their extremely small singlet–triplet energy gaps (ΔEST) of 79 and 134 meV, respectively. Consequently, the solution-processed non-doped OLEDs without any hole injection/transport layers featuring TB2CZ-ACTRZ and TB14CZ-ACTRZ as the TADF emitters demonstrated the maximum external quantum efficiencies (EQEs) of 9.5 and 8.1%, respectively, while the device fabricated with their simple emissive core ACTRZ had an EQE of only 1.2%. These results clearly demonstrated that the development of multifunctional TADF dendritic emitters is an extremely worthwhile objective for the realization of highly efficient solution-processable non-doped OLEDs with simple device architectures.

Three blue thermally activated delayed fluorescence (TADF) emitters containing a δ-pyridoindole donor moiety and diphenyltriazine acceptor moiety were designed, synthesized and characterized using photophysical and electroluminescence studies. Their photophysical properties and device performances were compared with those of control materials comprising a carbazole donor moiety. The functional properties were altered by different numbers and linking position of the δ-pyridoindole donor moiety. The δ-pyridoindole-substituted materials exhibited blue-shifted emissions and low-lying HOMO levels when compared to their control materials. The as-fabricated OLED devices based on these TADF emitters with a δ-pyridoindole donor demonstrated the blue electroluminescence property with maximum external quantum efficiency of 22.1% and CIE color coordinates of (0.16, 0.23). This result showed that heteroatom engineering in the molecular skeleton is an effective way towards designing highly efficient blue TADF emitters.

Three new derivatives containing silane cores, viz. 9,9′,9′′-(((4-(pyridin-3-yl)phenyl)silanetriyl)tris(benzene-4,1-diyl))tris(9H-carbazole) (SiCz3Py1), bis(4-(9H-carbazol-9-yl)phenyl)bis(4-(pyridin-3-yl)phenyl)silane (SiCz2Py2), and 9-(4-(tris(4-(pyridin-3-yl)phenyl)silyl)phenyl)-9H-carbazole (SiCz1Py3), were designed and synthesized. Carbazole as a donor and pyridine as an acceptor were tethered to tetraphenylsilane at different mole ratios. All three host materials showed high glass transition temperatures between 118 and 164 °C, which are different from those of the previous silane-based host materials (e.g., diphenyldi-o-tolylsilane (UGH-1), 1,4-bis(triphenylsilyl)benzene (UGH-2), and 1,3-bis(triphenylsilyl)benzene (UGH-3)). The triplet energies of these three hosts are observed at 2.85–2.90 eV, which is high enough for them to act as blue host materials in thermally activated delayed fluorescence organic light emitting diodes (TADF OLEDs). In particular, SiCz2Py2 and SiCz1Py3 hosted-TADF OLEDs demonstrated excellent performances, with a maximum external quantum efficiency (EQEmax) of 18.7 and 18.8%, respectively. Such good performances of SiCz2Py2 and SiCz1Py3 are originated by suppressing the non-radiative triplet decay and high reverse intersystem crossing (RISC) rate constant for efficient triplet to singlet up-conversion. This work demonstrates that tetraphenylsilane is a promising non-conjugate (i.e., sp3-hybridized) linkage core for developing a variety of high Tg host materials, particularly for blue TADF OLEDs.

In this paper, we report a promising molecular design concept to attain short exciton lifetime, appropriate triplet energy and high photoluminescence quantum yield (PLQY) in blue thermally activated delayed fluorescence (TADF) emitters for high quantum efficiency and better efficiency roll-off characteristics in organic light emitting diodes (OLEDs). Herein, new TADF molecules with nitrogen at α- and δ-positions of the carboline donor moiety were synthesized and their effects on the photo-physical and electroluminescence properties were theoretically and experimentally investigated. The TADF molecule with a δ-carboline donor moiety was much favorable for short exciton lifetime, high delayed PLQY, good blue color, and small singlet and triplet splitting compared to the generally used carbazole. A maximum external quantum efficiency (EQE) of 22.5%, reduced efficiency roll-off and good color purity with Commission Internationale de l'Eclairage (CIE) 1931 color coordinates of (0.19, 0.34) were exhibited by the blue OLED using the TADF emitter, 4,5-bis(5H-pyrido[3,2-b]indol-5-yl)phthalonitrile (δ-2CbPN). Moreover, the effectiveness of the δ-carboline donor moiety was verified in another deep blue TADF emitter, 5,5′-(2-(9H-carbazol-9-yl)-5-(4,6-diphenyl-1,3,5-triazin-2-yl)-1,3-phenylene)bis(5H-pyrido[3,2-b]indole) (CzDCbTrz). A maximum EQE of 23.4%, deep blue color, and reduced efficiency roll-off were attained in the CzDCbTrz based OLED.

New bipolar host molecules composed of carbazole, pyridoindole, and dibenzothiophene (DBT) were synthesized for blue thermally activated delayed fluorescence (TADF)-based organic light-emitting diodes (OLEDs). 2,8-Di(9H-carbazol-9-yl)dibenzo[b,d]thiophene, 9-(8-(9H-carbazol-9-yl)dibenzo[b,d]thiophen-2-yl)-9H-pyrido[2,3-b]indole, and 2,8-bis(9H-pyrido[2,3-b]indol-9-yl)dibenzo[b,d]thiophene were prepared based on the selective reactivity at the 2,8-positions of DBT. The new symmetric and asymmetric host materials exhibited high triplet energies (2.89–2.95 eV). 4,5-Di(9H-carbazol-9-yl)phthalonitrile (2CzPN) was selected as an emitting dopant for achieving sky-blue emissions in TADF-OLEDs. 2CzPN-doped TADF-OLEDs, whose configuration is ITO (50 nm)/HATCN (7 nm)/TAPC (75 nm)/host:6% 2CzPN (20 nm)/TmPyPB (50 nm)/LiF (15 nm)/Al (100 nm), showed low driving voltages and high external quantum efficiencies (EQEs). These results are attributed to the well-controlled bipolar character of the host giving a better charge balance in the emitting layer. In particular, the device containing ZDN:6% 2CzPN showed an unprecedentedly high EQE of 25.7% (at 0.074 mA cm−2).

High mobility group box protein 1 (HMGB1) is an abundant, conserved, non-histone nuclear protein that can serve as an alarmin, driving the pathogenesis of inflammatory and autoimmune diseases. In addition to its intracellular functions, HMGB1 can be released to the extracellular environment where it mediates the activation of the innate immune response, resulting in chemotaxis and cytokine release. HMGB1 contains three conserved redox-sensitive cysteines (C23, C45, and C106), and modifications of these cysteines determine the bioactivity of extracellular HMGB1. To advance our understanding of the redox-dependent functional changes of HMGB1, we have modeled full-length HMGB1 and simulated three different states of the protein, including its C23A and C106A mutants. Principal component analysis suggests that redox states affect the disordered loop movements, and subsequently the domain movements, of the active B-box domain that determines the fate of cytokine activity. We have also explored the free energy landscape of the redox states of HMGB1 to understand their crucial structural differences. These findings may have identified redox-dependent features that enable functional conformational transitions. Furthermore, active HMGB1 was docked onto a complex of Toll-like receptor 4 and myeloid differentiation factor 2 to predict the interactions that may provide helpful insights into the potential role of HMGB1 as therapeutic target for numerous autoimmune diseases.

We report a series of four bipolar host materials with indenocarbozole and biphenyl pyrimidine moieties for efficient phosphorescent green organic light-emitting diodes (OLEDs). All four host materials possess excellent electro-optical properties as well as good thermal and morphological stability due to their high glass transition temperature of 129 °C and decomposition temperature of 363–401 °C. The new materials also show good triplet energy of 2.76 eV and excellent charge carrier transport properties. The fabricated OLED device with 11-[3-(2,6-diphenyl-pyrimidin-4-yl)-phenyl]-12,12-dimethyl-11,12-dihydro-11-aza-indeno[2,1-a]fluorene (mDPPICz1) as green host shows maximum current and power efficiency as high as 75.8 cd A−1 and 87.1 lm W−1 at 1000 cd m−2, and an almost ideal external quantum efficiency of 21.7%.

New diketopyrrolopyrrole (DPP)-based π-extended conjugated polymers containing relatively long conjugated donor monomers were successfully synthesized in order to investigate their physical properties and device performance in thin-film transistors and photovoltaic cells. The solubility of the polymers was improved via side-chain engineering, and relatively high molecular weights were achieved by modifying the synthetic procedures. The highest occupied molecular orbital and the lowest unoccupied molecular orbital and optical bandgaps of the polymers were easily tuned by incorporating different donor monomers with different donating abilities. All polymers were highly crystalline with a predominant edge-on orientation on the substrate. The polymers displayed different hole mobilities in TFTs depending on the donor monomer. The highest mobility was 4.17 cm2 V−1 s−1, which was shown by the TFT fabricated with a terselenophene-containing DPP polymer after thermal annealing. Furthermore, bulk heterojunction organic photovoltaic cells made from a blend film of the polymers and (6,6)-phenyl C71-butyric acid methyl ester demonstrated promising device performance with power conversion efficiencies in the range of 3.48–5.05%.

This paper investigate the effectiveness of non-conjugated polymer polyvinylpyrrolidone (PVP) at the interface of an n-type metal oxide buffer layer and the photoactive layer in inverted bulk heterojunction solar cells. A 15% enhancement in power conversion efficiency (PCE) is realized after the incorporation of a thin PVP layer between zinc oxide (ZnO) and polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7):[6,6]-phenyl C71-butyric acid methyl ester (PC70BM) based photoactive layer in inverted polymer solar cells. The fabricated devices with the PVP layer show enhanced PCE as high as 7.30% under simulated AM 1.5 G (100 mW cm−2) illumination. The ZnO/PVP improves the electron extraction property of the ITO electrode, effectively blocks holes from the highest occupied molecular orbital of the donor, suppresses charge recombination at the interface of ZnO and the photoactive layer, and decreases the interfacial contact resistance.

Ultrathin but highly efficient dye-sensitized solar cells (DSCs) may be beneficial for making flexible devices and lowering production costs. Here, a uniform, ultrathin inverse opal (IO) electrode sensitized with a dithienothiophene (DTT)-based sensitizer (Carbz-PAHTDTT) was successfully prepared and demonstrated as a high-efficiency DSC electrode. The ultrathin IO was fabricated using a polystyrene opal template subsequently coated with TiO2 via a chemical vapor deposition approach. The Carbz-PAHTDTT-sensitized IO film was compared to an IO film sensitized by a conventional N719 dye. The charge collection efficiency of the Carbz-PAHTDTT-sensitized TiO2 IO electrode was comparable to the N719-sensitized electrode. However, the Carbz-PAHTDTT TiO2 IO electrode DSCs exhibited remarkably high light-harvesting efficiency due to high adsorption density and visible light absorption features of the Carbz-PAHTDTT-sensitized electrode. The Carbz-PAHTDTT DSCs containing a 3.5 μm thick IO electrode displayed a photocurrent density of 11.23 mA cm−2, which was 1.5 times higher compared to the N719-sensitized DSCs.

We report on the enhanced performance of polymer bulk heterojunction solar cells composed of an iridium complex with pendant sodium cations (pqIrpicNa) as an energy donor, poly(3-hexylthiophene) (P3HT) as an energy acceptor, polyethylene oxide (PEO) as an ion channel, and PCBM as an electron acceptor. With the iridium complex and PEO as additives, we observe a 20% increase in the current density, from 8.57 mA cm−2 to 10.24 mA cm−2, and a photoconversion efficiency of up to 3.4%. The observed enhancement in current density comes primarily from an efficient triplet–singlet energy transfer from the iridium complex to P3HT. Transient photoluminescence studies reveal triplet–singlet energy transfer efficiency from pqIrpicNa to P3HT of over 99%. Because of this high energy transfer efficiency, an enhancement is observed in the incident photon-to-conversion efficiency spectrum between 350 and 550 nm, which overlaps with the absorption range of the iridium complex. We also observe enhanced nanophase segregation of the active layer with pqIrpicaNa and PEO by atomic force microscopy. We propose that the observed enhancement in the current density stems not only from the enhancement in the morphology with the iridium complex, but also from the enhanced mobility of the sodium cations toward the metal electrodes through the ion channel of PEO under sunlight, which results in an increased charge collection at the electrodes.

In this paper, we demonstrate a facile, mild wetting (short residence time) poor solvent [isopropyl alcohol (IPA)] treatment, carried out on the top surface of a spin-cast poly (3-hexylthiopene) (P3HT) and [6,6]-phenyl-C71-butyric acid methyl ester (PCBM) blend film, in order to fabricate high-performance polymer solar cells (PSCs). This method utilizes the hydrophilic and polar/hydrogen bonding interactions of IPA with the blend components (P3HT and PCBM). The photovoltaic (PV) performance of the fabricated PSCs was optimized by utilizing a preheated IPA wetting treatment and devices fabricated with the configuration: ITO/PEDOT: PSS/P3HT:PCBM/M-IPA-T degrees/Al (T degrees: 25 degrees C/45 degrees C/65 degrees C/85 degrees C) (where "M" stands for modified IPA and "T" signifies the temperature used for the IPA wetting). Our investigation encompasses electrical, optical, crystalline, and morphological studies on the P3HT: PCBM blend films, modified by preheated IPA, to elucidate the associated enhancements in the PV characteristics and performance. The device fabricated with IPA-85 degrees C (ITO/PEDOT: PSS/P3HT: PCBM/M-IPA-85 degrees C/Al) exhibited the best power conversion efficiency (PCE) of 3.51%, with an open circuit voltage of 0.65 V, a fill factor of 0.52, and a short-circuit current density of 10.20 mA cm(-2). In contrast, the non-modified blend film device showed a PCE of only similar to 3.04%. Ultraviolet-visible absorption studies and X-ray diffraction results suggest that the use of the pre-heated mild-wetting IPA treatment improves the crystallinity and self-organization of the blend layer. We rationalize our findings based on the interactions between IPA and the blend components, due to its high polar and hydrogen bonding Hansen solubility parameters to impart supramolecular assembly of P3HT chains during the blend film formation. This is the first report demonstrating that the poor solvent (IPA) can induce an optimal phase separation in a P3HT: PCBM blend through our proposed mild wetting preheated treatment, toward achieving high-performance PSCs. Refereed/Peer-reviewed

Correction for ‘Novel dendritic large molecules as solution-processable thermally activated delayed fluorescent emitters for simple structured non-doped organic light emitting diodes’ by Mallesham Godumala et al., J. Mater. Chem. C, 2018, 6, 1160–1170.

We report highly transparent and low resistive new cathode structures, which basically consist of nano-composite layer/Ag/WO3 for transparent organic light-emitting diode (TOLED) applications. Our new cathode structure exhibits an extremely high transmittance of 91.2% at 550 nm, a low sheet resistance of 5.4 Ω □(-1), and excellent electron injection properties. Such a high transmittance along with a low resistivity of the fabricated new cathode could be explained by surface-modifying behavior with the generation of a nano-composite thin silver oxide layer during Ag deposition. Chemical interaction at the interface between the electron injection layer and the electron transport layer results in good electron injection properties in TOLEDs. The fabricated TOLEDs with our new cathode structures have a full device transmittance of 85-87% at 550 nm.

This paper demonstrates a comparative study of transition metal oxide materials, tungsten trioxide (WO3) and molybdenum trioxide (MoO3), as an effective hole extraction and transport layer in inverted polymer bulk heterojunction solar cells. Their device performances as an anode buffer layer are investigated based on thieno[3,4-b]thiophene/benzodithiophene (PTB7) and [6,6]-phenyl C70-butyric acid methyl ester(PC70BM) photoactive layers. The fabricated device with WO3 compared with MoO3 shows improved power conversion efficiency as high as 6.67% under a simulated AM1.5G illumination of 100 mW cm−2. The excellent performance of WO3 in inverted bulk heterojunction solar cells is attributed to an efficient hole extraction, excellent electron blocking capability, smooth morphology as well as better ohmic contact between the active layer and the metal electrode.

Two new hole-extraction materials, TPDI (5,10,15-triphenyl-5H-diindolo[3,2-a:3′,2′-c]carbazole) and TBDI (5,10,15-tribenzyl-5H-diindolo[3,2-a:3′,2′-c]carbazole), were synthesized and explored in planar heterojunction organic solar cells (OSCs). The synthesized materials have good transparency in the visible spectrum, high hole mobility, and compatible highest occupied molecular orbital (HOMO) values with the donor material, which make them excellent hole-extraction layers (HELs) for OSCs. The SubPc (subphthalocyanine chloride)/C60 and SubNc (subnaphthalocyanine chloride)/C60 OSCs with a TBDI HEL show impressive 35.9% and 29.1% improvements in power conversion efficiencies compared to reference devices. Their HOMO values were evaluated as 5.2–5.3 eV and hole mobilities were measured as 5.9–6.1 × 10−3 cm2 V−1 s−1 at 0.3 MV cm−1 by the space-charge limited current method.

Ferrocene compounds are promising redox shuttles for application in dye-sensitized solar cells (DSCs). Chemical modification of the cyclopentadienyl rings is easily achievable affording almost unlimited variation of the redox properties. This allows fine-tuning of the driving force for dye-regeneration and optimization of the energy conversion efficiency of DSCs. Herein, six ferrocene derivatives have been chosen for investigation which cover the large redox potential range of 0.85 V, by virtue of simple alkylation and halogenation of the cyclopentadienyl ring, and enable improved matching of the energy levels of the sensitizer and the electrolyte. Although the focus of this work was to examine the effect of the redox potential on charge transfer processes, DSCs were fabricated which achieved high energy conversion efficiencies of over 5%. Charge transfer reactions were studied to reveal the dependence of the dye regeneration rate, recombination losses and recombination pathways on the reaction driving force. An increase in redox potential led to a higher efficiency due to higher open circuit potentials until a threshold is reached. At this threshold, the driving force for dye regeneration (18 kJ mol−1, ΔE = 0.19 V) becomes too small for efficient device operation, leading to rapid recombination between the oxidized dye and electrons in the TiO2 conduction band. As a result of this work guidelines can be formulated to aid the selection of redox couples for a particular sensitizer in order to maximize the utilization of incident solar energy.

The photovoltaic performance of devices fabricated using three iridium complexes (1, 2, and 3) containing different main ligands (1-phenylisoquinoline, (4-isoquinolin-1-yl-phenyl)diphenylamine, and 1-pyren-1-yl-isoquinoline for 1, 2, and 3, respectively) was investigated. Two different devices, one fabricated by spin coating and one produced by vacuum deposition, were tested. Among the bulk heterojunction solar cells (BHJCs) fabricated by spin coating, the cell fabricated using 2 had the highest power conversion efficiency (PCE, 0.50%). The PCEs of 1 and 3 were 0.43% and 0.34%, respectively. These results suggested that the superior hole-transport ability of the triphenylamine moiety in 2 was responsible for the high photovoltaic performance of the device fabricated using this complex. This assumption was confirmed by fabricating electron-only devices using the three Ir complexes and comparing the turn-on voltage of each device. The photovoltaic performance of device C fabricated by the vacuum co-deposition of 2 and C60 in a 50 nm-thick active layer was 50% higher than that of device A (bilayer heterojunction solar cell) and device B (fabricated by the co-deposition of 2 and C60 with a 30 nm-thick active layer).

We have developed a novel host material, 9,9′-(2-((4-phenyl-1,2,3-triazol-1-yl)methyl)biphenyl-4,4′-diyl)biscarbazole (CBP-TA), for realizing highly efficient blue phosphorescent OLEDs. The maximum external quantum efficiency of the OLED device developed using CBP-TA doped with a blue phosphorescent material was 30% greater than that of a CBP-based device. This enhanced external quantum efficiency resulted from the bipolar properties of the new host, owing to which well-balanced hole and electron transport through the emitting layer was achieved. The excellent bipolar carrier transport properties of the new host were experimentally verified using various OLED device data.

We developed a new host material TCTEB with a conformationally homogeneous, sterically bulky structure due to nonbonded interactions between adjacent methylene groups. The host presented good thermal stability (Tg = 122 °C and Td = 321 °C) and high triplet energy (3.0 eV). The maximum quantum efficiency, current efficiency and power efficiency of the OLED device using the TCTEB host were 8.5%, 13.7 cd A−1, and 11.3 lm W−1, respectively, when doped with 8 wt% FIrpic.