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This study has proposed to use a well-defined oligomer F4TBT4 to replace its analogue polymer as electron acceptor toward tuning the phase separation behavior and enhancing the photovoltaic performance of all-polymer solar cells. It has been disclosed that the oligomer acceptor favors to construct pure and large-scale phase separation in the polymer:oligomer blend film in contrast to the polymer:polymer blend film. This gets benefit from the well-defined structure and short rigid conformation of the oligomer that endows it aggregation capability and avoids possible entanglement with the polymer donor chains. The charge recombination is to some extent suppressed and charge extraction is also improved. Finally, the P3HT:F4TBT4 solar cells not only output a high VOC above 1.2 V, but also achieve a power conversion efficiency of 4.12%, which is two times higher than the P3HT:PFTBT solar cells and is comparable to the P3HT:PCBM solar cells. The strategy of constructing optimum phase separation with oligomer to replace polymer opens up new prospect for the further improvement of the all-polymer solar cells.

The effect of groups in conjugated molecules on films interface morphology, electronic structure, and charge transport behavior is explored utilizing a series of crystalline organic heterostructures that are constructed by four rod-like molecules and vanadyl phthalocyanine (VOPc). The four rod-like molecules, which possess the same biphenyl endgroup but different central groups, present similar growth behavior along with different thin film structural parameters and electronic structures. The changes of the structure parameters result in diverse morphology of the VOPc/rod-like molecule heterostructure because of the different lattice mismatch. The electronic structure differences in rod-like molecules cause different interface electronic structure of the heterostructure. Under the conjunct effect of morphology and interface electronic structure, the transistors based on the crystalline heterostructures present diverse charge transport behavior and field-effect mobilities. These results provide a clue for the development of crystalline organic heterostructure engineering and tailoring overall organic device performance through molecular design in local inducing layer.

Two series of oligothiophenes (OThs), NaTn and TNTn (n = 2-6 represents the number of thiophene rings), end-capped with naphthyl and thionaphthyl units have been synthesized by means of Stille coupling. Their thermal properties, optical properties, single crystal structures, and organic field-effect transistor performance have been characterized. All oligomers display great thermal stability and crystallinity. ne crystallographic structures of NaT2, NaT3, TNT2, and TNT3 have been determined. The crystals of NaT2 and NaT3 are monoclinic with space group P2(1)/C, while those of TNT2 and TNT3 are triclinic and orthorhombic with space groups P-1(-) and P2(1)2(1)2(1), respectively. All oligomers adopt the well-known herringbone packing-mode in crystals with packing parameters dependent on the structure of the end-capping units and the number of thiophene rings. The shorter intermolecular distance in NaT3 compared to NaT2 indicates that the intermolecular interaction principally increases with increasing molecular length. X-ray diffraction and atomic force microscopy (AFM) characterization indicate that the NaTn oligomers can form films with better morphology and high molecular order than TNTn oligomers with the same number of thiophene rings. The NaTn oligomers exhibit mobilities that are much higher than those for TNTn oligomers (0.028-0.39 cm(2) V-1 s(-1) versus 0.010-0.055 cm(2) V-1 s(-1), respectively).

The relationship between the performance characteristics of organic field-effect transistors (OFETs) with 2,5-bis(4-biphenylyl)-bithiophene/copper hexadecafluorophthalocyanine (BP2T/F16CuPc) heterojunctions and the thickness of the BP2T bottom layer is investigated. Three operating modes (n-channel, ambipolar, and p-channel) are obtained by varying the thickness of the organic semiconductor layer. The changes in operating mode are attributable to the morphology of the film and the hetero-junction effect, which also leads to an evolution of the field-effect mobility with increasing film thickness. In BP2T/F16CuPc heterojunctions the mobile charge carriers accumulate at both sides of the heterojunction interface, with an accumulation layer thickness of ca. 10 nm. High field-effect mobility values can be achieved in continuous and flat films that exhibit the heterojunction effect.

New single-polymer electroluminescent systems containing two individual emission species—polyfluorenes as a blue host and 2,1,3-benzothiadiazole derivative units as an orange dopant on the main chain—have been designed and synthesized. The resulting single polymers are found to have highly efficient white electroluminescence with simultaneous blue (λmax = 421 nm/445 nm) and orange emission (λmax = 564 nm) from the corresponding emitting species. The influence of the photoluminescence (PL) efficiencies of both the blue and orange species on the electroluminescence (EL) efficiencies of white polymer light-emitting diodes (PLEDs) based on the single-polymer systems has been investigated. The introduction of the highly efficient 4,7-bis(4-(N-phenyl-N-(4-methylphenyl)amino)phenyl)-2,1,3-benzothiadiazole unit to the main chain of polyfluorene provides significant improvement in EL efficiency. For a single-layer device fabricated in air (indium tin oxide/poly(3,4-ethylenedioxythiophene): poly(styrene sulfonic acid/polymer/Ca/Al), pure-white electroluminescence with Commission Internationale de l'Eclairage (CIE) coordinates of (0.35,0.32), maximum brightness of 12 300 cd m–2, luminance efficiency of 7.30 cd A–1, and power efficiency of 3.34 lm W–1 can be obtained. This device is approximately two times more efficient than that utilizing a single polyfluorene containing 1,8-naphthalimide moieties, and shows remarkable improvement over the corresponding blend systems in terms of efficiency and color stability. Thermal treatment of the single-layer device before cathode deposition leads to the further improvement of the device performance, with CIE coordinates of (0.35,0.34), turn-on voltage of 3.5 V, luminance efficiency of 8.99 cd A–1, power efficiency of 5.75 lm W–1, external quantum efficiency of 3.8 %, and maximum brightness of 12 680 cd m–2. This performance is roughly comparable to that of white organic light-emitting diodes (WOLEDs) with multilayer device structures and complicated fabrication processes.

Light-emitting diodes exhibiting efficient pure-white-light electroluminescence have been successfully developed by using a single polymer: polyfluorene derivatives with 1,8-naphthalimide chromophores chemically doped onto the polyfluorene backbones. By adjusting the emission wavelength of the 1,8-naphthalimide components and optimizing the relative content of 1,8-naphthalimide derivatives in the resulting polymers, white-light electroluminescence from a single polymer, as opposed to a polymer blend, has been obtained in a device with a configuration of indium tin oxide/poly(3,4-ethyleiledioxythiophene)(50 nm)/polymer(80 nm)/Ca(10 nm)/Al(100 nm). The device exhibits Commission Internationale de I'Eclairage coordinates of (0.32,0.36), a maximum brightness of 11900 cd m(-2), a current efficiency of 3.8 cd A(-1), a power efficiency of 2.0 lm W-1. an external quantum efficiency of 1.50 %, and quite stable color coordinates at different driving voltages, even at high luminances of over 5000 cd m(-2).