Dark current/voltage response

Figure 5. Photosensitization vs. photoelectrocatalytic reactions. At top, the illuminated current/voltage curve is placed negative of the current/voltage response on bare Pt in the dark. At bottom the current/voltage curve indicates an increase in reaction rate, but no change in the apparent emf of the reaction.

The overall current voltage response of the cell, its current-voltage characteristic, can be approximated as the sum of the short circuit photocurrent and the dark current. The sign convention for photocurrent and voltage in photovoltaic is such that the photocurrent is positive. This is the opposite of the usual convention for electronic devices. With this sign convention, the net current density in the cell is given by... 

Doping densities in single-crystal semiconductor samples can usually be determined from capacitance and voltage measurements uing suitable electrolyte contacts. However, in the case thin polycrystalline layers fabricated for PV devices, dark currents arising from cracks and pinholes often make interpretation of impedance data difficult In this case a different approach based on analysis of the EQE response may be useful. If the minority diffusion length in the sample is sufficiently small to fulfill the condition aL 1-as is usually the case for... 

In this section we consider several of these photoemissive device specifications, stressing dark current, the choice of the electron-multiplier dynode material, and the design of the multiplier for optimization of speed or gain. Other device specifications, such as dynode operating voltages, ruggedness and physical size, are best found in the commercial literature [5.2,3, and, e.g., 5.135-138]. We conclude the chapter with a comparison of spectral response curves for classical and NEA devices. 

In-situ SPV measurements seem possible with minor modifications (1) the tip potential (versus the reference) is set at a value close to the rest potential of the semiconductor in darkness (this must be compatible with the electrochemical response of the tip), and (2) the tip current is quenched by adjusting the sample voltage (versus the reference) with the second feedback system. With p-type materials the method seems more obvious than with n-type specimens, since illumination promotes surface electrons. At n-type materials SPV measurements will induce corrosion since holes are driven to the interface. If absolute measurements of the SPV seem difficult, because they depend on the adjustment of the tip potential, differential measurements appear accessible to experiment. 

The polymerfilm was sdution coated onto a carbon loaded pdymer film substrate (MystR ) and then overcoated with an evaporated semi-transparent /d top contact Tlie darit current transient injection experiment is carried out by apidying the positive voltage step to the substrate contact and time resolving the transient response of the injected hde current The early time dark injection current is depicted in the insert and the time at which the maximum current occurs is denoted as t. According to the theory of transient space charge limited injection, the time tp can be rdated to the moUlity p of injected ludes from equation 3,... 

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