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We develop a series of polymer donors containing carbazole-based units (CBT) to achieve high-performance (PCE of 15.54%) and thermally stable PSCs.

New non-fullerene acceptors were synthesized by alkylthiothiophene side chain engineering and the material systems based on the acceptors demonstrated non-halogenated solvent processed indoor organic photovoltaics with an efficiency of 22.38% under 500 lux LED light.

Recently, the performance of organic photovoltaics (OPVs) has increased with the advent of non-fullerene acceptors, and significant efforts have been devoted to improving the performance via the side-chain engineering of Y6 and its derivatives.

Small-molecule acceptor (SMA)-based organic solar cells (OSCs) have achieved high power conversion efficiencies (PCEs), while their long-term stabilities remain to be improved to meet the requirements for real applications. Herein, we demonstrate the use of donor-acceptor alternating copolymer-type compatibilizers (DACCs) in high-performance SMA-based OSCs, enhancing their PCE, thermal stability, and mechanical robustness simultaneously. Detailed experimental and computational studies reveal that the addition of DACCs to polymer donor (

Intrinsically stretchable electronics can form intimate interfaces with the human body, creating devices that could be used to monitor physiological signals without constraining movement. However, mechanical strain invariably leads to the degradation of the electronic properties of the devices. Here we show that strain-insensitive intrinsically stretchable transistor arrays can be created using an all-elastomer strain engineering approach, in which the patterned elastomer layers with tunable stiffnesses are incorporated into the transistor structure. By varying the cross-linking density of the elastomers, areas of increased local stiffness are introduced, reducing strain on the active regions of the devices. This approach can be readily incorporated into existing fabrication processes, and we use it to create arrays with a device density of 340 transistors cm–2 and a strain insensitivity of less than 5% performance variation when stretched to 100% strain. We also show that it can be used to fabricate strain-insensitive circuit elements, including NOR gates, ring oscillators and high-gain amplifiers for the stable monitoring of electrophysiological signals. An all-elastomer strain engineering approach, which uses patterned elastomer layers with tunable stiffnesses, can be used to create intrinsically stretchable transistor arrays with a device density of 340 transistors cm–2 and strain insensitivity of less than 5% performance variation when stretched to 100% strain.

While the power conversion efficiencies (PCEs) of organic solar cells (OSCs) have been dramatically increased through the development of small molecular acceptors (SMAs), achieving eco-friendly solution processability of OSCs is a crucial prerequisite for their practical application. In this study, we develop three new, green solvent-processable SMAs (YSe–C3, YSe–C6, and YSe–C9) with different outer side-chains (n-propyl (C3), n-hexyl (C6), and n-nonyl (C9)), affording high-performance OSCs with non-halogenated solvent (o-xylene)-processed active layers. Also, the impact of both outer and inner side-chain engineering of these SMAs on the performance of eco-friendly fabricated OSCs is systematically investigated. The outer side-chain structure has a much more significant impact than the inner side-chain. For example, the PM6:YSe–C6 blend affords high-performance OSCs with a power conversion efficiency (PCE) of over 16%, whereas the PCEs of the YSe–C3- and YSe–C9-based OSCs are only 11–14%. The lower PCEs of PM6:YSe–C3 and C9 are mainly attributed to reduced electron mobility and increased charge recombination, resulting from aggregate-containing non-optimal blend morphologies. Interestingly, the well-optimized morphology of the YSe–C6-based blend also affords OSC devices with active layer thickness-independent PCEs, up to a thickness of >400 nm, demonstrating the great potential for large-area device manufacturing via an eco-friendly printing process. Thus, optimizing the outer side-chain structure of Y-series SMAs is essential for producing green solvent-processed high-performance OSCs.

Here we report a polymeric semiconductor (ODATT) comprising alkoxy anthracene (ODA) and thienothiophene (TT) polymerized by stille coupling reaction with the Pd catalyst. The optical properties of the polymer: PC71BM blend films are used by the UV-Visible absorption spectroscopy. The ODATT blends with PC71BM exhibit a maximal power conversion efficiency of 2.2% via thermal annealing treatment. Morphological analysis of the polymer: PC71BM blend films demonstrate the influence of ODATT polymer segregation on device performance by atomic force microscopy and transmission electron microscopy. We confirmed that ODATT has enhanced fill factor after thermal annealing treatment from the reduced series and shunt resistance from morphological enhancement.

Understanding the effects of the chemical structures of donor polymers on the photovoltaic properties of their corresponding organic photovoltaic (OPV) devices under various light-intensity conditions is important for improving the performance of these devices. We synthesized a series of copolymers based on poly[(2,6-(4,8-bis(5-(2-thioethylhexyl)thiophen-2-yl)benzo[1,2

The new donor-acceptor copolymer with triethylsilylethynylanthradithiophene as donor and bithiazole as acceptor, poly(triethylsilylethynylanthradithiophene-bithiazole) (PTesADT-BTz), was synthesized through stille coupling. The structure of obtained polymer was characterized by H NMR and FT-IR. The number average molecular weight (Mn) and weight average molecular weight (Mw) were measured to be 13 and 23 kDa, respectively, and the polydispersity index was 1.76. The polymer was analyzed by UV-visible spectroscopy, cyclovoltammetry, thermogravimetric analysis, and differencial scanning calorimetry. The organic field effect transistor (OFET) employing PTesADTBTz spin-cast from chloroform solutions at 100 °C annealing showed the mobility of 4.93 × 10−6 cm2/V·s, on/off ratio of 2.20 × 102, and a threshold voltage of 29.7 V.

We report a series of new n-type random copolymers (P(NDI2OD-Se-Th x), where x = 0, 0.5, 0.7, 0.8, 0.9, 1.0) consisting of naphthalene diimide (NDI), selenophene-2,2′-thiophene (Se-Th), and seleno[...

In contrast to the red and green regions, conventional fluorescent emitters continue to serve as blue emitters in commercialized organic light-emitting diodes. Many researchers have studied anthracene moieties as blue emitters, given their appropriate energy levels and good emission properties. We herein report two new deep blue-emitting anthracene derivatives that include

Jet printing of π-conjugated polymers synthesized through simple solution processes has been considered to be promising for the direct patterning of organic semiconductors on large-area substrates. However, it is still challenging to achieve direct patterns of high-performance polymer semiconductors through electrohydrodynamic jet printing because of the relatively low solubilities of donor–acceptor π-conjugated polymers which have high charge carrier mobilities and operation stabilities. A novel synthesis is proposed to obtain donor–acceptor π-conjugated polymer semiconductors suitable for printed electronics while exhibiting high performance of hole transport properties. The backbones and side chains of the donor–acceptor π-conjugated polymers are fully engineered to (1) achieve balanced jetting conditions and (2) provide time to induce the intermolecular self-assembly during the continuous printing. The printed polymers have similar morphologies and molecular orderings to those of spin-coated semiconductor films, which provide highly uniform electrical performances of organic field-effect transistors (OFETs) with a saturation mobility similar to those of the spin-coated films, up to 3.07 cm2 V−1 s−1. Furthermore, these high performances and operational stabilities suggest feasibility of the printed OFETs to be applied to ammonia gas sensors. Our study guides the design of π-conjugated polymers suitable for large-area printing processes to contribute to printed electronics.

A straightforward competent strategy to attune the solid-state morphology, opto-electronic and photovoltaic properties of conjugated co-polymers has been studied by inserting different percentages of N,N-dimethylthiophene-3-carboxamide (TDM) monomeric units. The TDM percentage was varied from 20 to 100%, resulting in widening of the energy band gap. Fabrication of solar cells was performed with ITIC-4F as an electron acceptor to accomplish power conversion efficiencies (PCEs) of 7.8% for P4 (minimum TDM) and 0.85% for P1 (maximum TDM) under a thermal tempering process. A drastic drop in the PCE was noted with increasing percentage of TDM which agrees well with the optical, electronic, and morphological studies. Morphological analysis revealed high crystallinity for P4:ITIC-4F blend having minimum percentage of TDM units compared to its counterparts of higher TDM percentages. A sharp increase in π-π stacking is seen with reduced percentage of TDM units, leading to d spacing of ̴ 3.6 Å. Detailed investigations regarding the charge carrier transport in relation to the π-π stacking of the polymeric film are well implemented in this work. © 2021, Korean Society for Precision Engineering.

Organic flash memories that employ solution-processed polymer semiconductors preferentially require internal stability of their active channel layers. In this paper, a series of new donor-acceptor copolymers based on cyclopentadithiophene (CDT) and diketopyrrolopyrrole (DPP) are synthesized to obtain high performance and operational stability of nonvolatile floating-gate memory transistors with various additional donor units including thiophene, thiophene-vinylene-thiophene (CDT-DPP-TVT), selenophene, and selenophene-vinylene-selenophene. Detailed analyses on the photophysical, two-dimensional grazing incident X-ray diffraction, and bias stress stability are discussed, which reveal that the CDT-DPP-TVT exhibits excellent bias stress stability over 10

We report two newly synthesized naphthalene diimide (NDI)-based conjugated polymers, poly[(E)-2,7-bis(2-decyltetradecyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone-vinylene-thiophene-viny...

A series of acene-modified small molecules have been designed and synthesized, and their photovoltaic characteristics were studied by using the small molecules in organic photovoltaics (OPVs). Different cores were introduced to modulate the conjugation lengths of the small molecules and the bulk heterojunction (BHJ) morphologies. Three small-molecule donors were prepared, namely Ph-TTR, Na-TTR, and An-TTR, which have phenyl, naphthalene, and anthracene moieties, respectively, as conjugated cores. These donors were synthesized in a few steps and exhibited favorable BHJ morphologies, thereby giving promising power conversion efficiencies (PCEs). The donors showed excellent miscibility with the acceptor PC71 BM, and the use of the additive 1,8-diiodooctane (DIO) led to a remarkable increase in crystallinity, thereby increasing the PCEs of their OPVs. Of the three donors, Na-TTR showed the most efficient charge carrier generation and favorable molecular packing structures; hence, of the three types of devices tested, the Na-TTR:PC71 BM devices exhibited the highest PCE, specifically 6.27 %, without pre- or post-treatments. The promising PCEs achieved from these easily synthesized acene-modified small molecules suggested that acene-modified small molecules can be useful materials in OPVs.

Herein, we explore the strategy of realizing a red-selective thin-film organic photodiode (OPD) by synthesizing a new copolymer with a highly selective red-absorption feature. PCZ-Th-DPP, with phenanthrocarbazole (PCZ) and diketopyrrolopyrrole (DPP) as donor and acceptor units, respectively, was strategically designed/synthesized based on a time-dependent density functional theory calculation, which predicted the significant suppression of the band II absorption of PCZ-Th-DPP due to the extremely efficient intramolecular charge transfer. We demonstrate that the synthesized PCZ-Th-DPP exhibits not only a high absorption coefficient within the red-selective band I region, as theoretically predicted, but also a preferential face-on intermolecular structure in the thin-film state, which is beneficial for vertical charge extraction as an outcome of a glancing incidence X-ray diffraction study. By employing PCZ-Th-DPP as a photoactive layer of Schottky OPD, to fully match its absorption characteristic to the spectral response of the red-selective OPD, we demonstrate a genuine red-selective specific detectivity in the order of 1012 Jones while maintaining a thin active layer thickness of ∼300 nm. This work demonstrates the possibility of realizing a full color image sensor with a synthetic approach to the constituting active layers without optical manipulation.

For color-pure phosphorescence organic light emitting diodes (PHOLEDs), we synthesized the trifluoromethyl sulfonyl substituted ligand and two new blue Iridium complexes with perfluoro-sulfonyl group (SOCF3pic and SOCF3mpic). The both iridium complexes showed similar photophysical and thermal properties while the HOMO energy leves of two Iridium complexes slightly differnet to be −5.84 eV for SOCF3pic and −5.74 eV for SOCF3mpic, respectively. The device with the SOCF3mpic dopant exhibited higher device efficiencies of 7.17 cd/A and 3.7% compared to that with the SOCF3pic dopant (4.03 cd/A and 2.78%). Two-dimensional GIXD images of scattered X-ray intensity from surface to full depth for SOCF3pic-doped and SOCF3mpic-doped TCTA:4PTPS films were characterized for preferential orientation along the out-of-plane direction.

Well-balanced ambipolar benzodifurandione (BDO) donor–acceptor copolymers were synthesized by tuning its intramolecular charge transfer nature by expanding the volumetric portion of the donor moiety, i.e., by using thiophene copolymerized with thiophene vinylene thiophene (TVT) or selenophene vinylene selenophene (SVS). Photophysical analyses revealed that BDO-SVS formed highly aggregated states in the solution state compared with BDO-TVT, facilitating a well-ordered self-assembled crystalline structure in the solid state. Using two-dimensional grazing incident X-ray diffraction and quantitative pole figure analyses, we established that the molecular orientation and degree of crystallinity was higher in BDO-SVS than in BDO-TVT. The morphological features identified by atomic force microscopy also showed a higher crystalline nature of SVS derivative, implying that SVS can strengthen intermolecular charge transport. This improved environment for charge transport, was revealed by the performance of organic field-effect transistors: BDO-SVS had superior performance than that of BDO-TVT for both hole and electron mobilities. This research shows that BDO, with a strong acceptor moiety, renders high-performance ambipolar characteristics when copolymerized with an expanded and aggregating donor moiety, such as SVS.

An acceptor-donor-acceptor (A-D-A) conjugated small molecule, DHII-EH-TR, was designed, synthesized, and its solar cell performance studied. The DHII-EH-TR molecule with its extended fused aromatic core had a narrow bandgap and displayed red-shifted absorption. To investigate its photovoltaic properties and device application, small molecule-based organic photovoltaics (SMOPVs) were fabricated having the conventional structure of ITO/PEDOT:PSS/DHII-EH-TR:PC70BM/ZnO NPs/Al (PEDOT:PSS, poly (3,4-ethylenedioxythiophene):polystyrene sulfonic acid; ZnO NPs, ZnO nanoparticles). Solar cells made with a blend of 1,8-diiodooctane with ZnO NPs generated the highest performance with a power conversion efficiency (PCE) of 3.60%. Charge dynamics and transport, microscopic thin film analysis, and morphology were studied to explain the performance of SMOPVs made with DHII-EH-TR.

Phenazasiline, a sp3 hybridized silicon-bridged diphenylamine, is a promising donor moiety for deep-blue TADF emitters because of its deep highest occupied molecular orbital, high triplet level of 3.1 eV, and orthogonal connection with acceptor moieties. Herein, we report highly efficient deep-blue TADF emitters composed of phenazasiline donor and triazine acceptor combined with methyl-substituted phenylene linkers. As a series of methyl-substituted linker-based TADF emitters, we also synthesized spiroacridine donor-based sky-blue TADF emitters to study the effect of methyl-substituted linkers on the photophysical properties of TADF emitters. Deeper blue emissions of TADF emitters were obtained by substituting either one or two methyl groups at the phenylene linker of TADF molecules, and a small singlet–triplet gap below 0.2 eV was maintained for efficient reverse intersystem crossing. Organic light-emitting diodes (OLEDs) with spiroacridine-based TADF emitters, TTSA and TXSA, showed external quantum effi...

We report a blue thermally activated delayed fluorescence compound based on a spiro-silicon-connected silafluorene–phenazasiline donor. By incorporating triphenyltriazine as an acceptor, the compound exhibited well-separated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels and charge transfer-type emission, confirmed by density functional theory (DFT) calculations and its solvatochromic characteristics. The compound exhibited blue emission with a photoluminescence (PL) peak at 469 nm, a high photoluminescence quantum yield (PLQY) of 68%, and a single-triplet energy gap of 0.20 eV in a DPEPO host matrix. Due to its co-planar silafluorene and triphenyltriazine moieties, the compound exhibited a high horizontal emission dipole ratio of 79%. Various electroluminescent devices of single host, mixed host, and interface exciplex structures were fabricated using the compound as the emitter. The external quantum efficiency (EQE), maximum brightness, and Commission Internationale de L’Eclairage (CIE) y-values ranged from 0.63 to 20.6%, 210 to 6930 nit, and 0.120 to 0.206, respectively, depending on the host materials and device structures. Among the fabricated EL devices, the DPEPO host device exhibited the highest EQE of 20.6% with CIE color coordinates of (0.150, 0.184).

In addition to attaining strong charge transport capability, field-effect transistors based on conjugated polymer thin films should be processed using non-chlorinated solvents for device fabrication, to avoid adverse impacts on human health and the environment. Although many high-performance diketopyrrolopyrrole (DPP) based conjugated polymers have been studied, few DPP based polymers that can be processed in non-chlorinated solvents have been reported to date. In this work, ambipolar polymeric semiconductors based on a DPP backbone that can be solution-processed using non-chlorinated solvents are reported. The DPP backbone combined with asymmetric conjugated segments results in high solubility and processability in non-chlorinated solvents, such as toluene and o-xylene, without disruption in the conjugation and molecular ordering of the main backbone. The polymer films fabricated with a high-boiling-point additive show ambipolar charge transport characteristics and highly enhanced electrical performance due to greatly enhanced intermolecular interactions and the resulting aggregated nanostructures. The combination of non-chlorinated solution processing with the green additive, along with ambipolar characteristics, enables high-performance environmentally friendly complementary logic circuit integration to be achieved.

The need for optoelectronic and chemical compatibility between the layers in colloidal quantum dot (CQD) photovoltaic devices remains a bottleneck in further increasing performance. Conjugated polymers are promising candidates as new hole-transport layer (HTL) materials in CQD solar cells (CQD-SCs) owing to the highly tunable optoelectronic properties and compatible chemistries. A diketopyrrolopyrrole-based polymer with benzothiadiazole derivatives (PD2FCT-29DPP) as an HTL in these devices is reported. The energy level, molecular orientation, and hole mobility of this HTL are manipulated through molecular engineering. By levering the polymer's optical absorption spectrum complementary to that of the CQD active layer, EQE across the visible and near-infrared regions is maximized. As a result, a PD2FCT-29DPP-based device exhibits a fill factor of 70% and approximately 35% efficiency enhancement compared to a PTB7-based device.

A new series of ITIC-based non-fullerene acceptors (NFAs), namely m-ITTC-Oeh-SM (IT-SM) and m-ITTC-Oeh-DSM (IT-DSM), which contain thiophene-substituted end groups (EGs) with single and double thiomethyl side chains, respectively, were designed, synthesized, and characterized in this study. The IT-SM NFA exhibited a narrower optical band gap, redshifted absorption, stronger crystallinity, and smoother surface morphology than those of the IT-DSM NFA. Organic solar cells (OSCs) based on the polymer donor PBDB-T and IT-SM reported a power conversion efficiency (PCE) of 8.98% with the addition of 0.5 v/v% 1,8-diiodooctane (DIO), whereas the PCE of the PBDB-T:IT-DSM device was equal to 3.02%. The difference between the PCE values of these two devices was attributed to the gap of the short-circuit current and fill factor. Detailed analyses of the charge transport, collection, and morphology of the blend films were performed to investigate the difference between the device performances. The results of this study can help formulate detailed guidelines for the commercialized production of NFAs.

Alternative acceptors for fullerene-derivatives need to be considered for indoor organic photovoltaics (OPVs) due to their spectrally inefficient light absorption ability and photo-instability which limits performance. Here, we report a highly efficient and photo-stable indoor OPV comprising an amalgamation of a wide band-gap donor(poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b’]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c’]dithiophene-4,8-dionz) and a modified ITIC-based NFA (3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis (4-hexylmeta-phenyl)-dithieno [2,3-2′,3′-d’]-s indaceno [1,2b:5,6b] dithiopheneethylexyloxy) (m-ITIC-O-EH)) with alkoxy side chains. Due to its excellent absorption properties in the near-infrared region, the m-ITIC-O-EH-based OPV exhibited an extraordinarily high maximum output power density (Pmax) (95.6 μW/cm2), >3 times greater than the Pmax (31.9 μW/cm2) of a reference fullerene acceptor-based (PC70BM) OPV under a 1000 lx halogen lamp (Pin = 8.4 mW/cm2). Furthermore, the m-ITIC-O-EH-based OPV exhibited satisfactory photo-stability with >80% retention of its initial power conversion efficiency (PCE) under the continuous light soaking of the halogen lamp (1000 lx) for 12 h. The high-indoor performance of the alkoxy-substituted NFA-based OPVs highlights their potential for implementation in Internet of Things applications.

We report on the synthesis and characterization of a novel naphthalene diimide (NDI)-based small molecule with a bithiophene linker unit, NDI-BT-NDI-EH, for application as a solution-processable n-channel active material in organic field-effect transistors (OFETs). NDI-BT-NDI-EH was synthesized via the Stille coupling reaction and the bithiophene linker unit was introduced as a rotatable linker between two NDI cores to improve the solubility of NDI-BT-NDI-EH while maintaining its high field-effect mobility. We found that the crystallinity and molecular ordering of NDI-BT-NDI-EH thin films could be improved by thermal annealing; a moderate annealing temperature of 120 °C appeared to be optimal for promoting self-organization among the NDI-BT-NDI-EH molecules. The NDI-BT-NDI-EH molecules in thermally annealed thin films mainly adopted an edge-on orientation with improved π-π stacking on the surface of octyltrichlorosilane-treated SiO2 substrates, which is favorable for lateral charge transport. As a result, the optimally annealed NDI-BT-NDI-EH OFET exhibited evident n-type OFET characteristics with high field-effect mobilities of up to 0.016 cm2 V−1 s−1 and an on/off ratio of 1.4 × 105.

We synthesized the heptaflurosulfonyl-substituted iridium complexes with SOCF7pic, SOCF7mpic, and SOCF7taz as a dopants for blue phosphorescent organic light emitting diodes (PHOLEDs). The ...

Two conjugated thienopyrrolodione-thiophene-vinyl-thiophene (TPDTVT)-based polymers, with one of them having an additional cyano (CN) group attached to the TVT building block, are synthesized and incorporated in photovoltaic device as electron-donating materials. Both TPD-TVT and TPD-TVTCN showed good thermal stability and appropriate solubility in chlorinated solvents, but they exhibited quite different optoelectrochemical and photovoltaic properties. The stronger intermolecular interactions of TPD-TVTCN, compared to TPD-TVT, lead to enhanced aggregation in blends with PC71BM. The domain sizes within 15–20 nm and improved molecular packing in TPD-TVTCN:PC71BM blend films result in better photovoltaic performance of TPD-TVTCN:PC71BM device compared to the device employing TPD-TVT.

To utilize the potential of small-molecule-based organic solar cells, proper designs of the photoactive materials which result in reasonable performance in a halogen-free solvent system and thickness tolerance over a range are required. One of the best approaches to achieve these requirements is via the molecular engineering of small-molecule electron donors. Here, we have modified a previously reported dithienobenzodithiophene (DTBDT)-based small molecule (SM1) via the dimerization approach, that is, the insertion of an additional DTBDT into the main backbone of the small molecule (SM2). An SM1-based photoactive film showed severe pinhole formation throughout the film when processed with a halogen-free o-xylene solvent. On the other hand, the modified small-molecule SM2 formed an excellent pinhole-free film when processed with the o-xylene solvent. Because of the dimerization of the DTBDT in the SM2 core, highly crystalline films with compact lamellae and an enhanced donor/acceptor interdigitation were formed, and all of these factors led to a high efficiency of 8.64% with chloroform and 8.37% with the o-xylene solvent systems. To the best of our knowledge, this study represents one of the best results with the SM donor and fullerene derivative acceptor materials that have shown the device performance with halogen-free solvents.

We report three DTBDT-based small molecules with various end groups and the effects of end-group tuning on their photovoltaic properties. We designed and synthesized DTBDT-Rho, DTBDT-EC, and DTBDT-CN, which have 3-ethylrhodanine, dicyanovinyl, and ethyl cyanoacetate, respectively, as end groups. DTBDT-EC and DTBDT-CN have much deeper LUMO and HOMO energy levels than DTBDT-Rho due to the stronger electron withdrawal of their end groups. As expected, the three DTBDT-based small molecules exhibit disparate bulk heterojunction blend morphologies and photovoltaic properties. DTBDT-Rho exhibits superior miscibility with PC71BM in blend films as well as crystalline structure within DTBDT-Rho domains, which result in solar cell devices with outstanding photovoltaic performances, namely PCEs above 7%. In contrast, DTBDT-CN gives rise to devices with poor performance of PCEs near 2%. It exhibits excessive molecular aggregation with less favorable molecular packing. Our study of end group tuning and morphological analysis provides valuable guidelines for the design of new small molecules and insight into their photovoltaic performances.

Vacuum-processed diphenylbis(3-(pyridine-2-yl)phenyl)silane (2PTPS), diphenylbis(3-(pyridine-3-yl)phenyl)silane (3PTPS), and diphenylbis(3-(pyridine-4-yl)phenyl)silane (4PTPS) have been used as electron-transporting host materials combined with tris(4-carbazoyl-9-ylphenyl)amine (TCTA) as the hole-transporting host, which induce balanced charge carrier transport for high-efficiency phosphorescent organic light-emitting diodes. The 4PTPS-based organic light-emitting diodes with tris[2-phenylpyridinato-C2,N]iridium(III) [Ir(ppy)3] dopant showed highest current efficiency and external quantum efficiency of 53.54 cd/A and 15.61%, compared to 2PTPS (40.75 cd/A, 11.84%) and 3PTPS (29.35 cd/A, 8.54%). These results were attributed to the well-aligned structure with preferential horizontal orientation of the emitting material layer by the diffraction intensity distribution as a function of azimuthal angle in two-dimensional grazing incidence X-ray diffraction analysis. The molecular orientation of TCTA:4PTPS material with a narrow azimuthal intensity distribution had better priority to the horizontal direction than the other TCTA:2PTPS and TCTA:3PTPS materials, which is related to the charge transport as well as the device efficiency. We found that the preferential horizontal orientation of the co-host material with a balanced charge carrier was not affected by Ir(ppy)3 dopant with a homoleptic structure and bis-[2-(4,6-difluorophenyl)pyridinato-N,C2](picolinato)iridium [Firpic] dopant with a heteroleptic structure in the co-host/dopant system.

We introduce a synthetic approach to enhance coalescence phenomenon during solidification of water-borne colloids so that thin, even, and continuous film morphology of polymer semiconductors can be realized. From the theoretical study of complex colloids, we show that small-sized and uniform colloid particles are essential to minimize depletion contact energy between colloid particles and thus to enhance coalescence. Therefore, the newly synthesized polymer semiconductor in this study is designed with the aim of better molecular affinity with surfactants, so that phase transfer of polymer semiconductors from organic phase to water phase can proceed more efficiently during mini-emulsion synthesis. This is achieved by substituting a Si atom to the branching C atom of the alkyl solubilizing group of a conventional donor–acceptor polymer semiconductor. Such a chemical modification increases the volumetric portion of hydrophobic alkyl chains and thus enables higher solubility as well as higher hydrophobicity, ...