Metal diffusion from magnesium–silver cathodes and indium–tin–oxide anodes in organic light-emitting diodes has been investigated. Magnesium showed no substantial diffusion under device operation and had no significant effects on luminance decay with operation time. Indium was immobile in storage at room temperature, while indium penetration into organic layers was observed after device operation. The presence of indium in organic films showed a correlation with performance degradation.

A series of intense photoluminescent (PL) polymers containing silyl groups with chain length from C1 to C18 has been successfully synthesized through polycondensation reaction. Introducing silyl groups into a conjugated polymer affords the polymer good processability, amorphousness, good film-forming ability, and sharp emission. A systematic analysis of this series of polymers indicates that increasing the side chain length of the polymers will slightly lower the thermal stability while increasing the molecular weight. UV−vis absorption and PL emission spectra of the polymers are quite similar. Cyclic voltammetric (CV) investigation of the polymers reveals that the side chain length plays an important role in the redox behavior of the polymers. Shorter side chain polymers possess better reproducibility of CV scans and higher peak currents, which implies that the chemical/electrical stability and charge injection and/or transporting ability for shorter side chain polymers are better than those for longer ones. Devices fabricated from poly[2,5-bis(decyldimethylsilyl)-1,4-phenylenevinylene] (DS-PPV) with the configuration of ITO/DS-PPV/Mg:Ag and ITO/PEDOT:PSS/DS-PPV/Mg:Ag indicate that the hole injection is the determining factor for device performance. Addition of the hole injection layer can improve the current efficiency and power efficiency by about 7 times and lower the turn-on voltage from 7.5 to 4.0 V for the two types of devices.

Bright organic electroluminescent devices having a metal-doped electron-injecting layerOrganic electroluminescent devices using SiO 2 as a hole-injecting buffer have been fabricated. With the presence of the buffer, the luminance of the device reaches 1820 cd/m 2 at the current density of 20 mA/cm 2 , which corresponds to an efficiency of 9.1 cd/A. The enhancements in brightness and efficiency are attributed to an improved balance of hole and electron injections due to blocking of the injected holes by the buffer layer and a more homogeneous adhesion of the hole transporting layer to the anode.

Attenuated total reflection Fourier transform infrared (FTIR) spectroscopy was used to characterize the surface species on oxide-free silicon nanowires (SiNWs) after etching with aqueous HF solution. The HF-etched SiNW surfaces were found to be hydrogen-terminated; in particular, three types of silicon hydride species, the monohydride (SiH), the dihydride (SiH(2)), and the trihydride (SiH(3)), had been observed. The thermal stability of the hydrogen-passivated surfaces of SiNWs was investigated by measuring the FTIR spectra after annealing at different elevated temperatures. It was found that hydrogen desorption of the trihydrides occurred at approximately 550 K, and that of the dihydrides occurred at approximately 650 K. At or above 750 K, all silicon hydride species began to desorb from the surfaces of the SiNWs. At around 850 K, the SiNW surfaces were free of silicon hydride species. The stabilities and reactivities of HF-etched SiNWs in air and water were also studied. The hydrogen-passivated surfaces of SiNWs showed good stability in air (under ambient conditions) but relatively poor stability in water. The stabilities and reactivities of the SiNWs are also compared with those of silicon wafers.

No abstract