Diodes behavior

Comparison of the spectral response and of the power efficiency of these first conjugated polymer/fullerene bilayer devices with single layer pure conjugated polymer devices showed that the large potential of the photoinduced charge transfer of a donor-acceptor system was not fully exploited in the bilayers. The devices still suffer from antibatic behavior as well as from a low power conversion efficiency. However, the diode behavior, i.e. the rectification of these devices, was excellent. 

The Schottky barriers were excellent diodes for films annealed at 600 °C, with turn on voltages of 0.6-0.8V and minimal reverse bias leakage.48 However, many of the contacts on the as-deposited films gave large reverse bias currents and nearly ohmic responses. This behavior is indicative of degeneracy of the semiconductor because of a high carrier density resulting from native defects. The improvement in the diode behavior of the annealed films is attributed to enhanced crystallinity and reduction of defects. 

CdO, a degenerate n-type semiconductor, was chemically deposited on single-crystal p-type Si [40]. The junction showed clear diode behavior, and, although no photovoltaic effect was observed, photocurrent was generated under reverse bias. From the spectral response of the photocurrent, almost all of the current generation occurred in the Si. 

Figure 4 Dark currents in DSSCs with the standard I /I2 redox couple (solid line) and with a kinetically much faster redox couple, ferrocene/ferrocenium, FeCp2 + /0. A = tetrabutylammonium. The charge-transfer resistance, Rct (see Fig. 1), of the 1 2 couple is 106 times greater than that of the FeCp2+/0 couple, leading to what is sometimes mistaken as diode behavior in the dark for the cell containing the 1 2 couple. (Data from Ref. 49.)...

Figure 29. Calculated current-potential characteristics for direct (dashed lines, 0/cm ) and surface state mediated electron transfer between an -type semiconductor electrode and a simple redox system. The plots show the transition from ideal diode behavior to metallic behavior with increasing density of surface states at around the Fermi-level of the solid (indicated in the figures). This is also clear from the plots below, which show the change of the interfacial potential drop over the Helmholtz-layer (here denoted as A(Pfj) with respect tot the total change of the interfacial potential drop (here denoted as A(p). Results from D. Vanmaekelbergh, Electrochim. Acta 42, 1121 (1997).

The selectivity of charge injection/extraction into/from the molecular HOMO or LUMO levels ensures the rectifying diode behavior of these organic devices [64]. The different working regimes of these MIM devices due to externally applied voltages are shown in Fig. 6. 

In this report, we demonstrate that robust electroplated Cu/n-Si(lll) junctions with a nearly perfect diode behavior may be grown from alkaline CuCN solutions (5). Results of investigations about aging of contacts in ambient are also presented. 

Possible applications of PANI-NTs in the construction of nanotip emitters in field-emission displays and polymer-based transistors have been demonstrated [238]. Gate voltage controllable p-n junction diode behavior for polymeric-acid-doped PANI-NTs with Au contacts, configured as a FET, was reported [334]. 

K. C. Aw, N. T. Salim, H. Peng, L. Zhang, J. Travas-Sejdic, and W. Gao, PN-junction diode behavior based on polyaniline nanotuhes field effect transistor, J. Mater. Sci.- Mater. Electron., 19, 996-999 (2008). 

Conventional semiconductor logic gates, such as AND, are produced by wired arrays of simpler switches, such as diodes or (in newer systems) transistors. Molecular electronic implementations can therefore do the same with a good chance for success. Heath, Stoddart, and colleagues use a monolayer of 10 sandwiched between metal and metal oxide layers and outer metallic contacts to produce diode behavior,"" several of which are known. 

Summary The use of differently substituted polysilanes as hole transport layers (HTL) in organic light-emitting diodes (OLEDs) was investigated. While hydrogen-substituted polysilanes deteriorate the diode behavior amino-substituted polysilanes lead to a significant improvement of the diode performance compared to a single-layer OLED. 

While polyphenylsilane (1) and poly(l-methyl-2-phenyldisilane) (2) rather deteriorate the diode behavior polyaminophenylsilane (3) strongly reduces the onset voltage of the devices and more than doubles the power efficiency and brightness compared to the single-layer LEDs. (Figs. 2, 3) These results compare favorably to the data Kido et al. reported for double-layer devices using Alqs as emissive layer and polymethylphenylsilane (PMPS) as HTL [2]. In this case a luminescence of 115 cd/m was measured at a current of 10 mA. For the device Al/Alqs/polyaminophenylsilane/lTO, 130 cd/m were obtained at the same current density. 

Figure 4.3.30. Typical steady-state photocurrent voltage curve. The thin Une is the current in the dark, which shows diode behavior. The thick line is the current under standard AM 1.5 solar irradiation.

The dark current-voltage characteristic shows the typical diode behavior with the applied voltage lowering the band bending, thus increasing exponentially the electron concentration at the surface and can be expressed as... 

For some logic gates, such as 1-bit adders, molecules with rectifying diode behavior are essential. Such an I(V) curve is displayed in Figure 6.6. This curve is used in some of the simulations presented in this chapter. This precise curve has not been obtained, however, a mononitro OPE was synthesized and its I(V) curve has a similar shape (see Figure 6.7). ... 

Inverters, NAND gates, half-adders and 1-bit adders have been found using the NanoCell simulator. For the inverters, NANDS, and half-adders, the simulated I(V) curve displayed in Figure 6.2 was used to characterize the on and off states of the molecular switches. A simulated I(V) curve with rectifying diode behavior was used for the 1-bit adder. 

Finally, a 1-bit adder has been trained (Figure 6.34) with a 70-nanoparticle, 1000-molecular switch NanoCell, where the molecules exhibit rectifying diode behavior as displayed in Figure 6.7. In Figure 6.34, the pins labeled A are set to the first input, those labeled B are set to the second input, and those labeled C are set to the third input. The output pins are labeled 1 and 2 . High input voltage is set at 1.8 V, while low input voltage is set at 0 V. The output pin is considered off if there is < 50 pA recorded. It... 

In the dark an TTO/MEH-PPV/Ca light-emitting device shows typical diode behavior. Above a tum-on voltage of 1.8 V the current increases exponentially with voltage and the polymo" electroluminesces below 1.3 V and under reverse bias almost no significant current flows due to the high resistance of the diode. However, under... 

Analysis of the forward as well as reverse bias conditions shows that the applied bias required in the reverse bias condition to achieve the transport through a D-B-A type of organic molecule, where the bridge acts as a barrier, is much higher compared to the forward bias condition. This is a typical diode behavior. 

Figure 3.9 Compares an ideal diode behavior with a non-ideal diode exhibiting series...

In this equation the added term a is called the diode ideality factor. The value of the ideality factor ranges from 1 for an ideal diode to at most 2. The latter occurs when the minority carrier diffusion lengths (before recombination) are small relative to the depletion width, W. The consequence of non-ideal diode behavior is shown in Figure 3.11. Effectively, the forward resistance of the diode can be doubled at a given voltage. 

Non-ideal diode behaviors (reverse leakage, series and shunt resistances, nonideal behavior, reverse breakdown) and the ideality factor. 

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