Photon-to-photocurrent efficiency

Quite differently, Pleux et al. tested a series of three different organic dyads comprising a perylene monoimide (PMI) dye linked to a naphthalene diimide (NDI) or C60 for application in NiO-based DSSCs (Fig. 18.7) [117]. They corroborated a cascade electron flow from the valance band of NiO to PMI and, finally, to C60. Transient absorption measurements in the nanosecond time regime revealed that the presence of C60 extends the charge-separated state lifetime compared to just PMI. This fact enhanced the device efficiencies up to values of 0.04 and 0.06% when CoII/m and P/Ij electrolytes were utilized, respectively. More striking than the efficiencies is the remarkable incident photon-to-current efficiency spectrum, which features values of around 57% associated to photocurrent densities of 1.88 mA/cm2. 

Steady-state wavelength-specific photocurrents were measured for the Ti-Fe-0 films in a two-electrode arrangement at different applied voltages. Incident photon-to-current efficiencies (IPCE) are calculated using the following equation ... 

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 32. Photocurrent spectra of the electrodes of Figure 31. IPCE, incident photon to current efficiency, sulfide electrolyte.

Some H- or J-type aggregates of porphyrins play a role as light harvesting assemblies to gather and transfer energy to the assembled devices, and to obtain a higher incident photon-to-photocurrent generation efficiency ( Kamat et al.,2000 Sudeep et al., 2002). 

PEC device efficiencies as measured by IPCE/EQE or STH implicitly include losses from impinging photons that are reflected or transmitted. To understand the inherent performance of a material, it is often helpful to subtract these losses and measure efficiency based only on photons absorbed. This is known as the absorbed photon-to-current efficiency (APCE), which describes the photocurrent collected per incident photon absorbed. APCE is synonymous with internal quantum efficiency (IQE). This is a particularly useful quantity to measure when studying thin films, since it helps to determine the optimum balance between maximal path-length for photon absorption versus minimal effective e /h" transport distance within the material. 

Enhancing the catalysis at the surface of PEC electrodes results in a lower kinetic overpotential and an increase in photocurrent. The effectiveness of the catalysts after surface treatment can be determined by utilizing three-electrode j-V measurements (see Section Three-Electrode j-V and Photocurrent Onset ) as well as IPCE measurements (see Chapter Incident Photon-to-Current Efficiency and Photocurrent Spectroscopy ). It may also useful to perform Mott-Schottky (see Section Mott-Schottky ) to determine any impacts these catalysts may have on the band structure (e.g., due to Eermi level pinning). 

Incident Photon-to-Current Efficiency and Photocurrent Spectroscopy... 

The incident photon-to-current efficiency (IPCE) is a measure of the ratio of the photocurrent (converted to an electron transfer rate) versus the rate of incident photons (converted from the calibrated power of a light source) as a function of wavelength. IPCE takes into consideration the efficiencies for photon absorption/... 

The partially-oxidized PANI film shows a higti photoelectrochemical activity. Figure 4 presents the photocurrent )ectra of the partially-oxidized and reduced PANI films on Au/p-ATP in Ihe same 0.05M Fe(CN)6 7 FeCCN) solutioa The incident-photon-to-current efficiencies (IPCE) are defined by the equation ... 

Fig. 2 Photocurrent spectrum for Ti02 (101) anatase sensitized with a mixture of the three cyanine dyes shown on the right of the figure. The solution spectrum is shown for comparison. IPCE stands for incident photon to current efficiency, i.e., it is the external quantum efficiency (Reproduced with permission from Ref [11])...

Figure 17 Photocurrent action spectra of bare nanocrystalline Ti02 film, and the sensitizers (1), (22), (24), and (57) adsorbed on Ti02 films. The incident photon to current conversion efficiency is plotted as a...

A very useful parameter for evaluating the performance of a photoelectrolysis cell is the incident photon to current conversion efficiency (IPCE). This is a measure of the effectiveness in converting photons incident on the cell to photocurrent flowing between the working and counter electrodes. IPCE is also called the external quantum efficiency. 

Fig. 4 Schematic illustration of the processes leading to photocurrent generation in organic solar cells, (a) Photon absorption in Step 1 leads to excitons that may diffuse in Step 2 to the donor/ acceptor (D/A) interface. Quenching of the exciton at the D/A interface in Step 3 leads to formation of the charge-transfer (CT) state. Note that processes analogous to Steps 1-3 may also occur in the acceptor material, (b) Charge separation in Step 4 leads to free polarons that are transported through the organic layers and collected at the electrodes in Steps 5 and 6, respectively, (c) The equilibria involved in Steps 1-4- strongly influence device efficiency...

Photovoltaic performance of the DSSC is described as follows Figure 8 shows the external spectral response curve of the photocurrent for nanocrystalline Ti02 solar cells sensitized by N3 and black dyes with the I /If redox mediator, where the incident photon-to-current conversion efficiency (IPCE) is represented as a function of wavelength. IPCE is obtained by the following equation ... 

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