Junction under illumination

Under potentiostatic conditions, the photocurrent dynamics is not only determined by faradaic elements, but also by double layer relaxation. A simplified equivalent circuit for the liquid-liquid junction under illumination at a constant DC potential is shown in Fig. 18. The difference between this case and the one shown in Fig. 7 arises from the type of perturbation introduced to the interface. For impedance measurements, a modulated potential is superimposed on the DC polarization, which induces periodic responses in connection with the ET reaction as well as transfer of the supporting electrolyte. In principle, periodic light intensity perturbations at constant potential do not affect the transfer behavior of the supporting electrolyte, therefore this element does not contribute to the frequency-dependent photocurrent. As further clarified later, the photoinduced ET... 

Fig. 10.12. Electronic processes occurring at a semiconduc-tor/electrolyte junction under illumination (Reprinted from E.

Fig. 5.29. Energy bands and quasi-fermi levels of a p-n junction under illumination...

Fig. 2.12 Energy diagram of a metal-semiconductor Schottky junction under illumination, a) Open circuit condition, b) short circuit condition...

Gautron J, Lemasson P, Rabago P, Tiiboulet R (1979) Electrochemical behavior of an aqueous electrolyte/I-doped ZnSe junction in the dark and under illumination. J Electrochem Soc 126 1868-1875... 

The solar to electric power conversion efficiency of dye-sensitized solar cells of laboratory scale (0.158 cm2), validated by an accredited photovoltaic calibration laboratory, has reached 11.1% under standard reporting conditions, i.e., air mass 1.5 global sunlight at 1000 Wm-2 intensity and 298 K temperature, rendering it a credible alternative to conventional p-n junction photovoltaic devices [68]. Photovoltaic performance data obtained with a sandwich cell under illumination by simulated AM 1.5 solar light using complex 26 are shown in Fig. 16. At 1 sun the 26-sensitized solar cell exhibited 17.73 =b 0.5 mA current, 846 mV potential, and a fill factor of 0.75 yielding an overall conversion efficiency of 11.18%. 

This view of Voc generation is additionally supported by the fact that the values of the temperature coefficient dUoc/dT = -(1.40-1.65) mVK-1 for the cells under the present study (with bilayer LiF/Al and ITO/PEDOT contacts) coincide with those for polymer/fullerene bulk heterojunction solar cells of the previous generation (with the same components of the active layer but without LiF and PEDOT contact layers) [156]. In this picture, the temperature dependence of Voc is directly correlated with the temperature dependence of the quasi-Fermi levels of the components of the active layer under illumination, i.e., of the polymer and the fullerene. Therefore, the temperature dependence of Voc over a wide range, and in particular V),c(0 K), are essential parameters for understanding bulk hetero junction solar cells. 

Flewig and Bloss [61] and Agostinelli et al. [62] have observed the same phenomenon in the chalcogenide solar cells. At higher voltages the junction current measured in the dark becomes smaller than the solar cell output current under illumination. Agostinelli et... 

A dark forward current 7d flows in the cell if a voltage is applied to the junction. To avoid confusion and for the sake of clarity we will call this current a junction current 7j measured in the dark, i.e. 7d = 7j(dark). This dark current continues to flow even if the cell is illuminated. The only requirement for the current to flow is that there should be a voltage at the junction. We designate this current measured under illumination as 7j(illumination). We need to introduce this notation because unlike in Si solar cells, in organic solar cells 7d = Tj(dark) is not equal to 7j(illumination). The junction current... 

This brings us to the rear support-film interface. What sort of barrier exists at this junction Are the electron exchange kinetics voltage-dependent at this interface The effect of changing the work function of the substrate on the current-voltage curves (in the dark and under illumination) has been investigated for Ti02 nanocrystalline films [344]. The onset potential for the photocurrent is found to be the... 

Figure 2.39a,b. Schematic picture of a solar cell with electron excitation and external circuit (a left) and current / vs. voltage V diagram under illumination (b above). 4, is short-circuit current, and is open-circuit voltage. The solar cell may consist of one or more p-n semiconductor junctions or of p-i-n amorphous junctions. 

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