IPCE value

With the D S SCs containing Hibiscus surattensis extract, the best performances were probably obtained because of the large amount of dye adsorbed on Ti02 (lxl cm2 active surface) in comparison with the other extracts from tropical flowers. Incident photon to current conversion efficiency (IPCE) values of 76% were calculated (2 — 590 nm). Jsc was 5.45 mAcm-2, Voc = 392mV, FF — 54%, and efficiency = 1.14%. Also, the stability of the photovoltaic devices was the best in the case of Hibiscus surattensis, even though it needs to be improved to achieve real long-term stability, especially as far as the sealing quality is concerned. 

Polo and Murakami Iha used anthocyanins extracted from jaboticaba (Myrciaria cauliflora Mart) and calafate (Berberis buxifolia Lam) as dyes for DSSCs. [46] The interaction between the dye molecules and Ti02 was identified by comparing the visible absorption spectra of the bare dye in solution with those acquired after dye absorption on the semiconductor a 15 nm red shift indicated the anchorage of the anthocyanin molecules on the Ti02 nanoparticles. The inorganic semiconductor layer was deposited on ITO and the electrolyte employed was I /I3 dissolved in acetonitrile. The photovoltaic cell obtained with the jaboticaba extract gave an IPCE value of 0.2 with a short-circuit current (/sc) of 7.2 mAcm 2, a Voc of 0.5 V and a fill factor of 54%. 

Comparison of IPCE Values Obtained with Various Sensitizers 744... 

Spray pyrolysis of ethanolic solutions of Fe(acetylacetone)3 or FeCls between 370°C and 450°C onto a glass substrate are reported for the fabrication of a-Fe20s thin-film photoanodes [75]. Upon illumination by a 150 W Xe lamp samples consistently demonstrate photocurrents of 0.9 mAcm , IPCE values up to 15%, and robust mechanical stability with no signs of photocorrosion for the undoped samples. With simultaneous multiple doping of 1% A1 and 5% Ti, an IPCE of 25% can be reached at 400 nm. Zn doping is known to induce p-type character in Ee20s thin film electrodes [76]. 

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 incident monochromatic photon-to-current conversion efficiency (IPCE) is plotted as a function of excitation wavelength. The IPCE value in the plateau region is 80% for complex 2, while for complex 25 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 2 as compared to the deprotonated complex 25. As a consequence, the short circuit photocurrent is 18-19 mAcrn-2 for complex 2, while it is only about 12-13 mA cm-2 for complex 25. However, there is a trade-off in photovoltage, which is 0.9 V for complex 25, as compared to 0.65 V for complex 2. Nevertheless, this is insufficient to compensate for the current loss. Hence, the... 

Photocurrent measurements performed for unmodified P25 point to an ra-type semiconductor behavior. Calculated IPCE values for P25... 

Fig. 4. Dependence of incident photon to current efficiency (IPCE) on excitation wavelength and presence of current-doubling agent. ITO electrodes were covered with P25 (squares) or 3% [PtCl4]/P25 (circles) and biased at a constant potential of 0.7 V vs. Ag/AgCl in 0.1 M NaOH solution (a)). After addition of 0.1 M HCOONa the IPCE values increased (open circles, (b)). The inserts show the zoomed visible 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... 

The latter two factors in this equation depend on kinetic factors, while LHE(A) depends on the nature of the light-absorbing sensitizer and the active (surface) area of the nanocrystalline surface. Measurements are normally carried out by using monochromatic light and the IPCE values are then calculated using the following equation ... 

A number of different approaches can be taken to investigate the charge-injection process. The first one, outlined in the last section, is based on the absorption rise observed at about 1200 nm which is associated with the presence of electrons in TiC>2. A second method is based on the measurement of the IPCE values for the assemblies in the presence of iodide, while the third approach is based on the intrinsic spectroscopic features of the sensitizer. In this present section, the focus is on the latter two approaches since the absolute rate for charge injection is not of direct interest but simply whether or not injection is taking place. To estimate the injection and charge-separation process, the transient absorption spectra of the sensitizer in solution are compared with those obtained in the interfacial supramolecular assembly. A typical example of this approach is shown in Figure 6.17 for the compound [Ru(dcbpy)2(bpzt)] [8], (see Figure 6.7 above for the structure). 

When the interfacial supramolecular triad is irradiated in the presence of I- under solar cells conditions, appreciable photocurrents are obtained. The profile of the photoaction spectrum shows clearly that photoinjection into TiC>2 takes place upon excitation of the ruthenium center. However, the IPCE values obtained are lower than those observed for the model compound, thus suggesting that injection is less efficient in the heterotriad. Of major interest is the mechanism for charge injection. Two different pathways can be envisaged. First, the charge injection may be a two-step process and takes place via the rhodium center as shown in the following equations ... 

The sensitization behavior of porphyrin with or without carboxylic acid groups was compared by Waclawik and co-workers. Their results indicate that the presence of carboxylic acid groups indeed generated higher IPCE values compared to that without carboxylic groups. The difference is ascribed to poor electronic coupling of the sensitizer without carboxylic acid groups to the titania conduction band [67]. 

The effects of the substituent at the para-position of mesophenyl on the sensitization properties of porphyrins (73) were also examined by the same group. All these novel darkgreen porphyrins yield IPCE values of up to 75% and overall power conversion efficiencies in the range of 5.1-7.1% under one sun in a liquid electrolyte... 

Sereno prepared a porphyrin dimer by connecting a metal free porphyrin to a zinc porphyrin with amid bond. The resulted porphyrin dimer was tested as a sensitizer for SnC>2 electrode. Even without anchoring groups, this porphyrin dimer showed sensitization to Sn02 electrode with an IPCE value of 10% at 420 nm [95]. 

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