The effects of substitute side chain were investigated using donor-acceptor (D-A) conjugated copolymers consisting of a cyclopentadithiophene (CPDT) derivative and dithienyl-benzothiadiazole (DTBT). The intrinsic properties of the copolymers were significantly altered by perturbations of the intramolecular charge transfer (ICT). The absorption of PCPDT-ttOTBTOT (P2), which assumed a tail-tail configuration, tended to blue-shift relative to the absorption of PCPDT-TBTT (P1). The absorption of PCPDT-hhOTBTOT (P3), which assumed a head-head configuration, was blue-shifted relative to that of P2. The electrical transport properties of field-effect transistors (FETs) were sensitive to the side chain position. The field-effect mobility in P2 (μ2=1.8×10–3 cm2/V·s) was slightly lower that in P1 (μ1=4.9×10–3 cm2/V·s). The mobility of P3, however, was very low (μ3=3.8×10–6 cm2/V·s). Photoexcitation spectroscopy showed that the charge generation efficiency (shown in transient absorption spectra) and polaron pair mobility in P1 and P2 were higher than in P3, yielding P1 and P2 device performances that were better than the performance of devices based on P3.

Though organic light emitting diodes are being commercialized in many applications, issues relating to lifetime and degradation remain as fundamental concerns limiting performance. A coherent understanding of degradation mechanisms is yet to emerge. We focus on intrinsic degradation of high quality Alq3 based diodes due to electrical stressing. We monitor progressive luminance degradation and recovery by introducing well defined relaxation time windows in the current stress cycles. The method helps to clearly distinguish between recoverable and permanent degradation systematically. The voltage shift due to degradation and recovery is also monitored as a function of time. Further, we introduce a method of reconstructing the transients of the recoverable part using progressive isolated current pulses as a probe. The recovery of degradation is related to the charging and discharging of the traps in the device and our method provides a technique of measuring significant parameters of trapping through luminance transients. The origin and distinguishing features of the two types of degradation are discussed.

The charge transport properties critically depend on the degree of ordering of the chains in the solid state as well as on the density of chemical or structural defects. In general, goodelectronic performance requires strong electronic coupling between adjace nt molecules in the solid-state that yield strong intermolecular π-overlap. Herein, we newly designed and synthesized organic semiconducting materials having both aryl (Ar) and perfluoroaryl (FAr) as substituents for organic electronics along with molecular packing control. Regarding this molecular design, we hypothesized and expected that the Ar and FAr substituents would induce well-defined π-π stacking structure of charge transport units for high performance organic electronics devices.

Easily available spin coating and vapor phase transport deposition techniques offer tremendous possibilities in fabricating inorganic/organic heterojunctions. We present here preliminary results from different thin film growth mechanisms including: i) PEDOT:PSS/Zn-nanowires/SiO2, ii) Zn-nanowires/PEDOT:PSS/SiO2, and iii) ZnO-nanowires/PEDOT:PSS/SiO2. The preliminary scanning electron microscopy and energy dispersive spectroscopy results show that Zn nanowires bond better to the non-annealed PEDOT:PSS thin films. It was also found that ZnO nanowires grow homogeneously on annealed PEDOT:PSS surfaces with colloidal Au nanoparticles as bonding reaction catalysts.

In this study, the open circuit voltage (VOC) of poly (3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) bulk heterojunction (BHJ) organic solar cells was measured at temperatures ranging from 300 K to 400 K. The temperature dependence of the vacuum shift and of the highest occupied molecular orbital (HOMO) energy level of P3HT and PCBM were measured by ultraviolet photoelectron spectroscopy (UPS) in the same temperature range. The temperature dependence of the absorption edge was also studied in the same temperature range to obtain the temperature variation of the optical band gap energy (Eg). The measured VOC of the devices showed a clear decreasing trend with increasing operating temperature and the total decrease was found to be about 0.1 V. Although the origin of VOC is still not fully understood it is generally believed that the energy level offset between the HOMO of the donor and the LUMO of the acceptor minus the exciton binding energy (0.3 eV) directly determines the value of VOC. However, by utilizing the measured values of the HOMO for the P3HT (donor) and of the LUMO for the PCBM (acceptor), we have found that the calculated values of VOC and its temperature dependence do not agree with the measured VOC values. This indicates that factors other than the offset between the HOMO of the donor and the LUMO of the acceptor materials are impacting VOC.

The development of materials with high stability and high charge mobility is urgent for commercial application of blue phosphorescent organic light emitting devices (PHOLED). Silicon based inorganic-organic hybrid materials with ultra high glass transition temperature (over 150 °C) and high charge mobility (over 1.16 x 10-3 at 5 x 105 V/cm) were synthesized. These showed high external quantum efficiency of over 19%, and deep blue color coordinates of (0.15, 0.23), when they were used as a host materials in the PHOLED.

The origin of the above interesting properties was investigated by experimental measurements complemented by DFT calculations. Estimations of the structure-property relationship of a molecule in an amorphous thin film would be presented

We measured the surface free energy of a substrate by transmission electron microscopy (TEM) using sub-millimetre-sized inkjet droplets. By employing two types of TEM grids with different surface free energies, we investigated the relationship between the surface energy and the patterns of an organic solution dried on the grids. We confirmed that the generation of the porphyrin hexamer [(H2PAC15)6TPh] patterns was affected by the surface free energy of the TEM grid.

Air-mediated molecular ordering in self-organized polymer semiconductors of regioregular poly(3-hexylthiophene) (P3HT) and poly[(9,9′-dioctylfluorenyl-2,7-diyl)-(2,2′-bithiophene-5,5′-diyl)] (F8T2) was investigated using organic field-effect transistors (OFETs) fabricated by transfer-printing using poly(dimethylsiloxane) stamps with various surface energies. OFET measurements revealed that the charge transport in the polymer semiconductors via the air interface layer was better than that via the substrate interface layer. The results indicated that the formation of a highly ordered microstructure at the polymer/air interface through air-mediated self-organization occurs in many polymer semiconductors. This air-mediated self-organization was weaker than substrate-mediated self-organization, whose influence appeared in OFETs with thin semiconductor films.

The space charge region width of the Schottky barrier that forms on the interface between aluminum and organic semiconductor polymer of bulk-heterojunction organic photodiodes has been investigated according to reverse voltage bias over the device and the capacitance-voltage characteristics. Here, we investigated the space charge region widths according to incident light power. Comparison of the mathematical models and experimental data measured under different light power indicate that effect of light on the space charge region of photodiodes is similar to the effect of base-emitter voltage on the space charge region of base-emitter junction in bipolar junction transistors.