Chien-Lung Wang

Influences of the Non-Covalent Interaction Strength on Reaching High Solid-State Order and Device Performance of a Low Bandgap Polymer with Axisymmetrical Structural Units

A high organic field-effect transistor mobility (0.29 cm(2) V(-1) s(-1) ) and bulk-heterojunction polymer solar cell performance (PCE of 6.82%) have been achieved in a low bandgap alternating copolymer consisting of axisymmetrical structural units, 5,6-difluorobenzo-2,1,3-thiadiazole. Introducing the fluorine substituents enhanced intermolecular interaction and improved the solid-state order, which consequently resulted in the highest device performances among the 2,1,3-thiadiazole-quarterthiophene based alternating copolymers.

Porphyrin‐Incorporated 2D D–A Polymers with Over 8.5% Polymer Solar Cell Efficiency

A copolymerization strategy is developed to utilize porphyrin as a complementary light-harvesting unit (LHU) in D-A polymers. For polymer solar cells (PSCs), the presence of LHUs increases the short-circuit current density (Jsc ) without sacrificing the open-circuit voltage (Voc ) and fill factor (FF). Up to 8.0% power conversion efficiency (PCE) is delivered by PPor-2:PC71 BM single-junction PSCs. A PCE of 8.6% is achieved when a C-PCBSD cathodic interlayer is introduced.

Giant Molecular Shape Amphiphiles Based on Polystyrene–Hydrophilic [60]Fullerene Conjugates: Click Synthesis, Solution Self-Assembly, and Phase Behavior

This paper reports a comprehensive study on the synthesis and self-assembly of two model series of molecular shape amphiphiles, namely, hydrophilic [60]fullerene (AC(60)) tethered with one or two polystyrene (PS) chain(s) at one junction point (PS(n)-AC(60) and 2PS(n)-AC(60)). The synthesis highlighted the regiospecific multiaddition reaction for C(60) surface functionalization and the Huisgen 1,3-dipolar cycloaddition between alkyne functionalized C(60) and azide functionalized polymer to give rise to shape amphiphiles with precisely defined surface chemistry and molecular topology. When 1,4-dioxane/DMF mixture was used as the common solvent and water as the selective solvent, these shape amphiphiles exhibited versatile self-assembled micellar morphologies which can be tuned by changing various parameters, such as molecular topology, polymer tail length, and initial molecular concentration, as revealed by transmission electron microscopy and light scattering experiments. In the low molecular concentration range of equal or less than 0.25 (wt) %, micellar morphology of the series of PS(n)-AC(60) studied was always spheres, while the series of 2PS(n)-AC(60) formed vesicles. Particularly, PS(44)-AC(60) and 2PS(23)-AC(60) are synthesized as a topological isomer pair of these shape amphiphiles. PS(44)-AC(60) formed spherical micelles while 2PS(23)-AC(60) generated bilayer vesicles under identical conditions. The difference in the self-assembly of PS(n)-AC(60) and 2PS(n)-AC(60) was understood by the molecular shape aspect ratio. The stretching ratio of PS tails decreased with increasing PS tail length in the spherical micelles of PS(n)-AC(60), indicating a micellar behavior that changes from small molecular surfactant-like to amphiphilic block copolymer-like. For the series of PS(n)-AC(60) in the high molecular concentration range [>0.25 (wt) %], their micellar morphological formation of spheres, cylinders, and vesicles was critically dependent upon both the initial molecular concentration and the PS tail length. On the other hand, the series of 2PS(n)-AC(60) remained in the state of bilayer vesicles in the same concentration range. Combining both of the experimental results obtained in the low and high molecular concentrations, a systematic morphological phase diagram was constructed for the series of PS(n)-AC(60) with different PS tail lengths. The versatile and concentration-sensitive phase behaviors of these molecular shape amphiphiles are unique and have not been systematically explored in the traditional surfactants and block copolymers systems.

Three-dimensional actuators transformed from the programmed two-dimensional structures via bending, twisting and folding mechanisms

Combining the physical principle of actuators with the basic concept of photonic crystals, colour-tunable three-dimensional (3D) photonic actuators were successfully fabricated. By controlling the d-spacings and the refractive index contrasts of the self-assembled 3D colloidal photonic crystals, colours of the photonic actuators were tuned. Various shapes of these 3D actuating objects were constructed by transforming the programmed 2D structures via bending, twisting and folding mechanisms. These 2D structures were first programmed by breaking the symmetry. The selective swellings were then applied as driving forces to control the shapes and colours of the photonic actuators. Scroll photonic actuators had been first demonstrated by bending the traditional 2D cantilever structure (K.-U. Jeong, et al., J.Mater.Chem., 2009, 19, 1956). By breaking the symmetry of a cantilever structure perpendicular to its long axis, polypeptide-/DNA-like 3D helical photonic actuators were obtained from the programmed 2D structure via twisting processes. Both left- and right-handed scrolls and helices with various colours can be achieved by changing the polarity of solvents. Different types of 3D actuators, such as cube, pyramid and phlat ball, were also demonstrated via the folding mechanism. The reversible 3D photonic actuators transformed from the programmed 2D structures via the bending, twisting and folding mechanisms may be applied in the field of mechanical actuators, and optoelectronic and bio-mimetic devices.

A Porphyrin–Fullerene Dyad with a Supramolecular “Double‐Cable” Structure as a Novel Electron Acceptor for Bulk Heterojunction Polymer Solar Cells

Bulk heterojunction (BHJ) polymer solar cells (PSCs) offer a promising, low-cost, large-area, fl exible, light-weight, clean, and quiet alternative energy source for both indoor and outdoor applications. [ 1–4 ] Power conversion effi ciencies (PCEs) in response to solar AM1.5 radiation as high as 6–8% have been reported for BHJ PSCs. [ 5 , 6 ] In order to achieve PCEs over 10%, BHJ materials capable of generating higher short circuit current ( J sc ) and larger open circuit voltage ( V oc ) are required. [ 7 , 8 ]

Hierarchical structure and polymorphism of a sphere-cubic shape amphiphile based on a polyhedral oligomeric silsesquioxane–[60]fullerene conjugate

A shape amphiphile composed of covalently linked spherical and cubic nanoparticles with distinct symmetry ([60]fullerene (C60) and polyhedral oligomeric silsesquioxane (POSS)) was synthesized and its solid state structures were characterized. The two types of nanoparticles are known to be generally immiscible, but they were connected with a short covalent linkage forming an organic–inorganic dyad (POSS–C60) which exhibited interesting crystallization characteristics. Crystals of the dyad exhibited polymorphism with two different crystal structures: an orthorhombic and a hexagonal unit cell with symmetry groups of P21212 and P6, respectively, both of which formed an alternating bi-layered structure of POSS and C60. The different symmetry groups in the polymorphs were attributed to the different packing orientations of the POSS within each layer. In the orthorhombic unit cell, one set of the edges of the POSS moieties is parallel to the c-axis; while in the hexagonal unit cells the body-diagonal is parallel to the c-axis of the crystal. Based on the crystal packing structure and density differential, it has been determined that the hexagonal unit cell structure is the more thermodynamically stable phase. This type of bi-layered structure with an alternating conductive fullerene and insulating POSS layer structure is of great interest for various potential applications such as nano-capacitors.

Control of preferred orientation with slow crystallization for carbon-based mesoscopic perovskite solar cells attaining efficiency 15%

To produce mesoscopic carbon-electrode-based solar cells free of a hole-conduction layer, we developed a simple one-step drop-cast method (temperature 20 °C, relative humidity 50%) to grow uniform and compact perovskite nanocrystals via slow crystallization (SC). X-ray diffraction (XRD) results indicated that perovskite nanocrystals produced inside the mesoporous TiO2/Al2O3/C layers according to our SC approach with N-methyl-2-pyrrolidone (NMP) as a precursor solvent showed a preferred orientation at facet (004) with large crystalline grains, whereas those produced with other solvents or via thermal annealing (TA) methods showed greater intensity at facet (220) with small crystals. After the SC (NMP) procedure was completed, additional TA treatment would change the preferred orientation from (004) back to facet (220), which would break the connectivity and lose the uniformity of the crystals, causing the grains to become significantly smaller. Transient photoluminescence (PL) decay profiles of the SC devices made with four precursor solvents, NMP, γ-butyrolactone (GBL), dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), were recorded to show the trend of charge separation kinetics of the perovskite crystals inside the mesoporous films, which is consistent with the trend of the corresponding device performance showing the same order. The SC (NMP) device attained the best efficiency of power conversion (PCE), 15.0%, with average value (13.9 ± 0.5%), which is much superior to those devices from either the traditional one-step TA (DMF) method (5.2 ± 1.0%) or the traditional sequential TA method (10.1 ± 0.7%). This work emphasizes the significance of the control of preferred orientation of perovskite nanocrystals using the SC approach, to obtain high-performance carbon-based mesoscopic solar cells with excellent reproducibility and stability.

A Facile PDMS‐Assisted Crystallization for the Crystal‐Engineering of C60 Single‐Crystal Organic Field‐Effect Transistors

Poly(dimethylsiloxane) (PDMS)-assisted crystallization (PAC) is a facile method to produce oriented C60 crystal arrays. Changing the drying mechanism from evaporation to solvent absorption (by PDMS) widens the solvent selection and facilitates the engineering of both the macroscopic shape and the microscopic lattice structure of the crystal arrays. The method also shows the potential to be applied to other organic semiconductors and large-area production.

A supramolecular structure with an alternating arrangement of donors and acceptors constructed by a trans-di-C60-substituted Zn porphyrin derivative in the solid state

When a molecule is constructed from geometrically isotropic [such as [60]fullerene (C60)] and anisotropic (such as porphyrin) units, as in the case of a trans-di-C60-substituted Zn porphyrin derivative (diZnCPD), great interest lies in the understanding of their individual contributions to structural formations and phase transitions. For this purpose, the compound, diZnCPD, was designed and synthesized. Its phase behavior was investigated viadifferential scanning calorimetry (DSC) and polarized light optical microscopy (POM) and its supramolecular structure was elucidated viawide-angle X-ray diffraction (WAXD) and selective area electron diffraction (SAED) in transmission electron microscopy (TEM). The diZnCPD possesses a polymorphism in its ordered structures. When cooled from the isotropic (I) phase with experimentally accessible rates, instead of transferring into its ultimate stable phase, this compound formed a less ordered, metastable phase with a layered structure at 152 °C. Annealing this metastable phase enabled a further transformation into a stable phase with a higher transition temperature. As such, this metastable phase is monotropic. The formation of the stable phase was thus thermodynamically favorable, but kinetically more difficult (with a higher barrier for the transformation). Direct formation of this stable phase from the I state was unsuccessful even after prolonged isothermal experiments over several days above 152 °C, indicating that the formation barrier of this stable phase is extremely high. The thermally stable phase possessed a supramolecular structure with a triclinic unit cell of a = 3.34 nm, b = 2.01 nm, c = 1.88 nm, α = 89°, β = 98°, and γ = 90°. Detailed structural analysis revealed that this is a donor–acceptor separated structure of C60s and porphyrins nearly along the [01] direction within which the zig-zag shaped C60 channels are along the [001] direction of the unit cell. We believe this is the first example of generating a donor–acceptor separated structure of C60s and porphyrins in the bulk through a thermal annealing process. This structure provides promising potential for the use of this material to fabricate supramolecular electronic devices without utilizing a solvent process.

Synthesis and morphological studies of a poly(5,6-difluorobenzo-2,1,3-thiadiazole-4,7-diyl-alt-quaterchalcogenophene) copolymer with 7.3% polymer solar cell efficiency

To obtain a poly(5,6-difluorobenzo-2,1,3-thiadiazole-4,7-diyl-alt-quaterchalcogenophene) (P(FBT-alt-CP4)) copolymer with a small optical band gap (Eg), and to achieve high short-circuit current (Jsc) in the P(FBT-alt-CP4) : PC71BM polymer solar cells (PSCs), P(FBT-alt-Se2Th2), which contains selenophene-2,5-diyl (–Se–) π-bridges, was synthesized. P(FBT-alt-Se2Th2) shows a Eg of 1.56 eV and is strongly aggregated in solution. Wide angle X-ray diffraction (WAXD) and grazing incidence X-ray diffraction (GI-XRD) results revealed the high solid-state order of P(FBT-alt-Se2Th2) and its edge-on orientation on the substrate. It delivered a high hole mobility (μh) of 0.36 cm2 V−1 s−1 in organic field-effect transistors (OFETs). The strong aggregation tendency of P(FBT-alt-Se2Th2) caused large segregation domains in the P(FBT-alt-Se2Th2) : PC71BM thin film, as is seen in the high-resolution transmission electron microscopy (HR-TEM) images. The addition of 8 vol% of 1-chloronaphthalene (1-CN) effectively suppressed the aggregation and led to more homogeneous active layer morphology. The improved morphology enhanced the Jsc of the PSCs. A superior PCE of 7.34% with a Voc of 0.70 V, a Jsc of 15.8 mA cm−2, and a FF of 66.4% was achieved in the inverted P(FBT-alt-Se2Th2) : PC71BM PSCs. The strong aggregation of P(FBT-alt-Se2Th2) is likely related to its more straight conjugated backbone according to the theoretical calculation results of the FBT-alt-Se2Th2 repeat unit.