In this study, we demonstrated a blue phosphorescent organic light-emitting diode (BPOLED) based on a host with two carbazole and one trizole (2CbzTAZ) moiety, 9,9′-(2-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)-1,3-phenylene)bis(9H-carbazole), that exhibits bipolar transport characteristics. Compared with the devices with a carbazole host (N,N’-dicarbazolyl-3,5-benzene, (mCP)), triazole host (3-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole, (TAZ)), or a physical mixture of mCP:TAZ, which exhibit hole, electron, and bipolar transport characteristics, respectively, the BPOLED with the bipolar 2CbzTAZ host exhibited the lowest driving voltage (6.55 V at 10 mA/cm²), the highest efficiencies (maximum current efficiency of 52.25 cd/A and external quantum efficiency of 23.89%), and the lowest efficiency roll-off, when doped with bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic) as blue phosphor. From analyses of light leakage of the emission spectra of electroluminescence, transient electroluminescence, and partially doped OLEDs, it was found that the recombination zone was well confined inside the emitting layer and the recombination rate was most efficient in a 2CbzTAZ-based OLED. For the other cases using mCP, TAZ, and mCP:TAZ as hosts, electrons and holes transported with different routes that resulted in carrier accumulation on different organic molecules and lowered the recombination rate.

This work proposes a novel, highly sensitive, and simple structure based on a tapered polymer as a tilt fiber sensor to sensitively measure tilt angles (θ). The fiber-optic tilt sensor consists of a tapered polymer and single-mode fibers (SMF), into which the tapered polymer to generate a bent in the sensor that is strongly correlated with θ. The used tapered polymer in the tilt sensing is the temperature (T) insensitive. It is further combined with a general fiber Bragg grating (FBG) as a temperature indicator for achieving simultaneous measurement of inclination (θ) and ambient T. The endface of the fiber is coated with a gold film to increase the light reflectivity and improve the measurement range. Experimental results show that when the sensor tilts, the reflective optical power changes significantly with high sensitivity, and the peak wavelength of FBG shifts when T varies. Both parameters can be measured simultaneously with good discrimination. An average tilt angle sensitivity of approximately 4.23 dB/deg. and a high resolution of 0.009 deg. are achieved in a θ variation from −6 to +6 deg. Simulations were performed and the numerical results were in good agreement with the experimental measurement.

We have demonstrated a vertically stacked device consisting of organic photovoltaic device (OPV) and organic light-emitting diode (OLED) inside a polymer dispersed liquid crystal (PDLC) cell. In such a device, OLED and PDLC acted as transmissive- (T-) and reflective- (R-) mode, respectively, of a transflective display without the tradeoff of aperture ratio between R- and T-modes in a conventional transflective LC display. OPV functioned as the black background for PDLC operation and increased the contrast ratio of OLED. Electrical characteristics of OLED and OPV in the stacked device were nearly identical to their individual device, which showed the fabrication process had little effect on OLED and OPV performances. However, their optical properties showed a little degradation, coming from the multi-layer structure and hence the suitable optical cavity design was needed. Storage lifetime of OLED increased in the stacked device because LC material helped to prevent the water and oxygen attack. Driving voltage of PDLC increased due to the insertion of passivation layer upon the electrode which was used protect the OLED and OPV underneath.

We developed cobalt and carbon complex materials as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs) to replace conventional platinum (Pt) CEs. Co12 and Co15, both of which are basic cobalt derivatives, showed good redox potential with a suitable open-circuit voltage (V_OC); however, their poor electrical conductivity engendered a low short-circuit current (J_SC) and fill factor (FF). Mixing them with carbon black (CB) improved the electrical conductivity of the CE; in particular, J_SC and FF were considerably improved. Further improvement was achieved by combining cobalt derivatives and CB through thermal sintering to produce a novel CoCB material as a CE. CoCB had good electrical conductivity and electrocatalytic capability, and this further enhanced both J_SC and V_OC. The optimized device exhibited a power conversion efficiency (PCE) of 7.44%, which was higher than the value of 7.16% for a device with a conventional Pt CE. The conductivity of CoCB could be further increased by mixing it with PEDOT:PSS, a conducting polymer. The device’s J_SC increased to 18.65 mA/cm², which was considerably higher than the value of 14.24 mA/cm² for the device with Pt CEs. The results demonstrate the potential of the cobalt and carbon complex as a CE for DSSCs.

The stamping process of self-assembled monolayers (SAMs) with polydimethylsiloxane (PDMS) mold on the Ag electrode was demonstrated, for use as the anode of a top-emission organic light-emitting device (OLED) and the cathode of an organic photovoltaic (OPV) device stacked underneath. Such SAMs reduce the barrier for hole injection from the Ag to the hole-transport layer of OLED. The PDMS mold coated with SAMs can be used repeatedly, for more than nine times. In this tandem device, the power conversation efficiency under OPV-mode operation and the current efficiency under OLED-mode operation were nearly identical to those in individual devices without compromise.