IPCE, photocurrent action spectra

The photocurrent action spectrum of the 0TE/Sn02/(Mes-Acr+-C00-Ti02 + C60)n electrode is compared with those of OTE/SnO2/(C60)n and OTE/Sn02/ (Mes-Acr+-COO-Ti02)n electrodes in a standard three-compartment cell under a bias of 0.2 V vs. SCE (Fig. 13.22a) [80], The photocurrent action spectrum of the 0TE/Sn02/(Mes-Acr+-C00-Ti02 + C60) electrode shows a maximum IPCE value of 37 % at an applied potential of 0.2 V vs. SCE (spectrum a in Fig. 13.22a). Under same experimental conditions the IPCE values are much smaller... 

The photocurrent action spectra of these complexes show broad features covering a large part of visible spectrum, and display a maximum at around 550 nm, where the incident monochromatic IPCE exceeds 85%. These hydrophobic complexes show excellent stability towards water-induced desorption when used as CT photosensitizers in nanocrystalline Ti02-based solar cells.62... 

The spectral response, or action spectrum, of a phototodiode is obtained by measuring the electrical response of the device upon monochromatic illumination over a wide range of wavelengths. The external quantum efficiency ij, often also called the incident photon-to-current efficiency (IPCE) of the device, is the ratio of the measured photocurrent (in electrons per unit area and time) to the intensity of incoming monochromatic light in photons per unit area and time. Explicitly,... 

Figure 3.3 Photocurrent density-voltage characteristics under lOOmWcm" incident intensity of AMI.5 simulated sunlight and IPCE action spectrum for an N719-sensitized Ti02 ITO-PEN electrode. This cell exhibits 6.1% efficiency.

Figure 4 shows the photocurrent action spectra of three typical cells under short circuit conditions [20]. Three different dyes were used to sensitize the heterojunction. In all three cases the action spectrum matches closely the absorptivity spectrum of the sensitizing dye. Solid-state heterojunctions sensitized with the mero-cyanine dyes (structure see Fig. 4) used in this study showed higher peak IPCE values when compared to Ru(lI)L2(SCN)2-sensitized junctions. Strongly improved... 

Figure 2 shows some representative photocurrent action spectra for the Ti02 electrode alone and in the presnce of the complex tris(4,4 -dicarboxy-2,2 -bipyridine)Ru(II), [Ru(dcbpy)3] and electron donors (bromide or iodide). Plotted are light-to-electrical conversion efficiency for monochromatic radiation as monitored by photocurrent, as a function of wavelength of irradiation. The features of the photocurrent action spectra are similar to the absorption spectrum in homogeneous solution. The incident photon conversion efficiency (IPCE) obtained with the Ru-complex is >70% at the absorption maximum in the visible light region. 

The mixed SAM under discussion here has been designed to overcome this limitation and to increase the photocurrent efficiency in the visible part of the spectrum. The strong overlap of the emission spectrum of BoDy with the absorption of Fc-P-C6o in the 500 nm region is anticipated to facilitate efficient energy transfer between the two species. The photochemical action spectra of the mixed monolayer show contributions from both BoDy and Fc-P-C6o- The overall behavior of the assembly is therefore in agreement with the scheme shown in Figure 5.34. At 510 nm, a much increased quantum yield for photocurrent production of 50 % is obtained. This study shows that photocurrents can be created at metal electrodes. Relatively high photocurrent efficiencies are obtained however, the fact that flat surfaces are used rather than the nanocrystalline approach taken for semiconductor substrates (see Chapter 6) means that the incident photocurrent efficiency (IPCE) values are... 

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