Charge limit

The results of several studies were interpreted by the Poole-Erenkel mechanism of field-assisted release of electrons from traps in the bulk of the oxide. In other studies, the Schottky mechanism of electron flow controlled by a thermionic emission over a field-lowered barrier at the counter electrode oxide interface was used to explain the conduction process. Some results suggested a space charge-limited conduction mechanism operates. The general lack of agreement between the results of various studies has been summari2ed (57). 

The electrical current of a coplanar interdigilal gold/LPPP/gold device is space charge limited due to p-type charge earner traps localized in the bandgap [28]. This can be inferred from the field dependence of the dark current at room temperature. The thermally stimulated current spectrum exhibits two peaks, corresponding to two distinct trap levels ,1 and ,", which can be calculated from the rise in current, /, below the peak temperature ... 

Two main methods have been used to measure the charge carrier mobility in electroluminescent polymers time of flight (TOF) carrier transit time measurements and analysis of the current-voltage (1-V) characteristics of single carrier devices in the space charge-limited current (SCLC) regime. A summary of the results for the hole mobility of PPV and PPV-related polymers is given in Table 11-1 [24, 27-32]. For... 

The hole current in this LED is space charge limited and the electron current is contact limited. There are many more holes than electrons in the device and all of the injected electrons recombine in the device. The measured external quantum efficiency of the device is about 0.5% al a current density of 0.1 A/cm. The recombination current calculated from the device model is in reasonable agreement with the observed quantum efficiency. The quantum efficiency of this device is limited by the asymmetric charge injection. Most of the injected holes traverse the structure without recombining because there are few electrons available to form excilons. 

One result of the field-dependent mobility is that the space charge-limited current (SCLC, the maximum current that can How in the bulk of the sample) does no longer follow a simple V2H scaling [132] on the voltage Land sample thickness L. Muigatroyd [133] was able to show that, for a mobility as in Eq. (13.4), the monopolar SCLC current could be well approximated by ... 

For typical polymer LED device parameters, currenl is space charge limited if the energy barrier to injection is less than about 0.3-0.4 eV and contact limited if it is laiger than that. Injection currents have a component due to thermionic emission and a component due to tunneling. Both thermionic emission and tunneling... 

Monarkite. Brit permitted mining expl contg typically NG 12.0, AN 4.97, Na chloride 24.5, Na nitrate 7.5, starch 4.0, mineral jelly 2.0, and collodion cotton 0.3%. Its charge limit is 26oz, and power by BalPend is 2.61 inches... 

Neuwestfalit. A Ger Favier-type permissible expl contg AN 70.3, DNT 10.9, Na chloride 16.8 flour 2.0%. Trauzl test value 309cc charge limit 540g... 

Generally similar but NiMH transitions are more subtle. Backup temperature termination recommended Similar, but with NiMH, cold temperature charge limit is 15°C NiMH slightly higher than NiCd... 

A. Van der Ziel, Space-Charge-Limited Solid-State Diodes... 

A.J. Campbell, D.D.C. Bradley, H. Antoniadis, M. Inbasekaran, W.W. Wu, and A.P. Woo, Transient and steady-state space-charge-limited currents in polyfluorene copolymer diode structures with ohmic hole injection contacts, Appl. Phys. Lett., 76 1734-1736, 2000. 

Important electrical informations about OLEDs, such as charge transport, charge injection, carrier mobility, etc., can be obtained from bias-dependent impedance spectroscopy, which in turn provides insight into the operating mechanisms of the OLED [14,15,73,75 78]. Campbell et al. reported electrical measurements of a PLED with a 50-nm-thick emissive layer [75], Marai et al. studied electrical measurement of capacitance-voltage and impedance frequency of ITO/l,4-Mv-(9-anthrylvinyl)-benzene/Al OLED under different bias voltage conditions [76], They found that the current is space-charge limited with traps and the conductivity exhibits power-law frequency dependence. 

This means that with increasing scan rate or lowering the solution concentration, the effect of lc will increase. Because a peak-shaped CV can only be obtained at a sufficiently high scan rate, the effect of electrode capacitance charging limits the CV application in low-concentration solutions. SWV has been developed to overcome this problem and to increase the quantitative accuracy of voltammetric techniques. The concentration for recording a SW voltammogram can be as low as a hundredth of that for recording a CV. 

Fig. 10 Schematic PE brush structure. In a we show the weakly charged limit where the counterion cloud has a thickness d larger than the thickness of the brush layer, h. In b we show the opposite case of the strongly charged limit, where all counterions are contained inside the brush and a single length scale d h exists...

The different free energy contributions lead, upon minimization with respect to the two length scales h and d, to different behaviors. Let us first consider the weak charging limit, i.e. the situation where the counterions leave the brush, d>h.ln this case, minimization of Fion + Fint with respect to the counterion height d in the limiting case of vanishing brush height (h = 0) and monomer volume = 0) leads to... 

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