Incident monochromatic IPCE

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 other important aspect in dye-sensitized solar cells is water-induced desorption of the sensitizer from the surface. Extensive efforts have been made in our laboratory to overcome this problem by introducing hydrophobic properties in the ligand. The heteroleptic complexes containing hydrophobic ligands of the type [Ru(dcbpy)(mhdbpy)(NCS)2] 1, [Ru(dcbpy)(dtdbpy)(NCS)2] 2 [Ru(dcbpy) (mddbpy)(NCS)2] 3 (dcbpy = 4,4 -dicar-boxy-2,2 -bipyridine, mhdbpy = 4-methyl-4 -hexadecyl-2,2 -bipyridine and dtdbpy = 4,4 -ditridecyl-2,2 -bipyridine, mddbpy = 4-methyl-4 -didodecyl-2,2 bipyridine) have been synthesized (Fig. 6). The photo-current action spectra of these complexes show broad features covering a large part of visible spectrum and displays a maxima around 550 run, where the incident monochromatic IPCE exceeds 80%. The performance of these hydrophobic complexes as CT photosensitizers in nanocrystaUine Ti02-based solar cell shows excellent stabdity toward water-induced desorption [55]. 

Lewis and coworkers have synthesized and characterized two osmium complexes [OsL2(CN)2] and [OSL3] (L = 4,4 -dicarboxylic acid-2,2 -bipyridine). In their studies they found nearly 80% incident monochromatic IPCE [66]. 

The incident monochromatic IPCE is plotted as a function of excitation wavelength. The IPCE value in the plateau region is 80% for complex 1, whereas for complex 3 it is only about 66%. In the red region, the difference is even more pronounced. Thus, at 700 nm the IPCE value is twice as high for the fully protonated complex 1 as compared to the deprotonated complex 3. Consequently, the short-circuit photocurrent... 

The incident monochromatic photon-to-current conversion efficiency (IPCE), also called external quantum efficiency, is defined as the number of electrons generated by light in the external circuit divided by the number of incident photons as a function of excitation wavelength. It is expressed in Equation (7).29 In most cases, the photoaction spectrum overlaps with the absorption spectrum of the sensitizer adsorbed on the semiconductor surface. A high IPCE is a prerequisite for high-power photovoltaic applications, which depends on the sensitizer photon absorption, excited state electron injection, and electron transport to the terminals ... 

IPCE Incident monochromatic photon-to-current conversion efficiency... 

Fig. 2 Incident monochromatic photon to electrical conversion efficiencies (IPCE) for bare polycrystalline Ti02 electrode and in the presence of Ru(dcbpy)3.

The incident monochromatic photon-to-current conversion efficiency (IPCE), sometimes referred to also as the external quantum efficiency (EQE), is another fundamental measurement of the performance of a device. The IPCE value corresponds to the photocurrent density generated in the external circuit under monochromatic illumination of the DSSC divided by the photon flux that strikes the cell [6]. From such an experiment, the IPCE as a function of wavelength can be calculated from the following formula ... 

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,... 

Fig. 5 Photocurrent vs potential plot recorded for a ca. 45 pm thick nanoparticulate Ti02 film, immersed in a 0.1 M HCIO4/0.1 M HCOOH solution and irradiated with a 300-nm monochromatic light (700 pW cm ) from the side of the film/solution boundary. On the left axis is represented the corresponding incident photon-to-current conversion efficiency (IPCE). In the insert is represented schematically (marked in grey ) the illuminated part of the Ti02 film where the electron injection takes place. (Reproduced with permission from [12])...

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 short circuit photocurrent, Jsc, is defined as integral over the solar spectrum of the monochromatic incident photon to current conversion efficiency (IPCE) of the solar cell under short circuit cmiditions ... 

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