Open-Circuit Decay Method

O Brien. 1235 Ohmic drop, 811, 1089, 1108 Ohmic resistance, 1175 Ohm s law, 1127. 1172 Open circuit cell, 1350 Open circuit decay method, 1412 Order of electrodic reaction, definition 1187. 1188 cathodic reaction, 1188 anodic reaction, 1188 Organic adsorption. 968. 978. 1339 additives, electrodeposition, 1339 aliphatic molecules, 978, 979 and the almost-null current test. 971 aromatic compounds, 979 charge transfer reaction, 969, 970 chemical potential, 975 as corrosion inhibitors, 968, 1192 electrode properties and, 979 electrolyte properties and, 979 forces involved in, 971, 972 977, 978 free energy, 971 functional groups in, 979 heterogeneity of the electrode, 983, 1195 hydrocarbon chains, 978, 979 hydrogen coadsorption and, 1340 hydrophilicity and, 982 importance, 968 and industrial processes, 968 irreversible. 969. 970 isotherms and, 982, 983... 

Whereas the charge-injection method is a small-amplitude perturbation method in which measurement is conducted during open-circuit decay, we now discuss a different open-circuit measurement, in which the initial overpotential is high, in the linear Tafel region. The equations we need to solve are similar to Eqs. 9K and lOK, except that the value of the current in Eq. lOK is that corresponding to the linear Tafel region, namely... 

Fig. 7K Charge injection followed by open-circuit decay (the coulostatic method). Diffusion limitation (low values of /x ) slows down the decay transient, as expected from the equivalent circuit shown in Fig. 2K.

Whereas the charge-injection method is a small-amplitude perturbation method, in which measurement is conducted during open-circuit decay, we now discuss a... 

A version of the galvanostatic method is that where the current is turned off (or a current f = 0 is applied ) and the polarization decay curve is measured. Consider an electrode which up to the time t = 0, when the current was turned off, had the potentiaf F at the net current density When the current is turned off, the ohmic voftage drop in the electrolyte gap between the electrode and the tip of the Luggin capillary vanishes, so that the potential instantaneously shifts to the value F (Fig. 12.11). After that the electrode potential returns (falls) relatively slowly to its open-circuit value, for which a certain nonfaradaic charging current is required. Since ip + =... 

There are numerous techniques to measure the recombination lifetime. Some of the better known are photoconductive decay (13). diode reverse recovery (14). diode open circuit voltage decay (15). surface photovoltage (JL ) and forward-biased pn junction I-V characteristic (17. I will describe one particular photoconductive decay method, because it is a relatively new, non-contact method that requires no junctions. This makes it very suitable for a large number of measurements as for a process sequence characterization tool. 

As described, the alternative method for the deduction of radical kinetics is the use of ESR transient signals [65, 66]. Transient signals are obtained by open-circuiting an electrode which was previously at a potential corresponding to the diffusion-limited current. The electrode is open circuited by opening a switch, rather than stepping the potential between two defined values since the latter method may produce contributions to the radical decay from, e.g. re-oxidation of a radical anion, if the latter is generated by... 

A number of characterization methods for wafers are used today. One group of experiments aims at the purely electronic parameters like DLTS and Photoluminiscence. While DLTS and related measurements give information on the trap energies, methods like surface photovoltage (SPV) or open circuit voltage decay (OCVD) give information on effective diffusion length. 

What is impUed by unequal generation and recombination lifetimes The lifetime measurement techniques and the resulting lifetimes measured with them must be clearly understood to avoid confusion. For example, the recombination lifetime is measured by such methods as photoconductive decay, open-circuit voltage decay, diode reverse-recovery, surface photo voltage, electron-beam induced current and others. 

The open-circuit voltage decay (OCVD) lifetime characterization technique was one of the early lifetime measurement methods. [76] It is simple and is among the preferred lifetime characterization techniques because it is easy to implement It requires only a simple measurement circuit. The interpretation of the experimental data is fairly straightforward and a commercial instrument is available. 

Bisquert J, Zaban A, Greenshtein M, Mora-Serd I (2004) Determination of rate constants for charge transfer and the distribution of semiconductor and electrolyte electronic energy levels in dye-sensitized solar cells by open-circuit photovoltage decay method. J Am Chem Soc 126 (41) 13550-13559... 

Recombination is either characterized using steady state measurements, for instance in the dark or under open-circuit conditions, or transient methods where the decay of the concentration of charges is used to analyze the strength and type of recombination. To determine the recombination rate itself is not useful because the continuity equations are solved in terms of the charge densities of electrons and holes on which the recombination rate is strongly dependent. Therefore, we need to measure directly a recombination lifetime r or an effective recombination prefactor k, which is usually defined as k = R/rP, where n is the average excess electron and hole concentration. Typically, these measurements are done by transient photovoltage measurements [31, 42, 148-152], by transient absorption measurements [148, 153] or by impedance measurements [154—156]. 

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