**4.2 fs-TA**

As many ongoing processes of DSSCs are relatively fast ones, one needs a technique with high time-resolution to follow such processes in DSSCs. One of the most utilized techniques to follow such processes is the fs-TA setup [18–25]. Simply, in fs-TA, one needs a laser source of short pulses in the range of 100 fs per pulse, and by overlapping two laser pulses at the measuring sample (one to start the reaction 'pump', and another to probe it), the resulted spectrum at the detector provide exceptional information about both the ground state and the excited state of the reaction, **Figure 4** shows a simple scheme for utilizing fs-TA setup. The pump pulse is usually in the visible range to promote a charge transfer, and the probe pulse can be usually in the visible or in the infrared range [14, 26, 27]. The main advantages of fs-TA are the ability to detect dark states that are not observed by other timeresolved emission techniques such as charge transfer, energy transfer, intersystem crossing, and charge recombination [28–30].

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**Figure 5.**

**4.3 fs-TE**

**Figure 4.**

energy of the emitted photons [12, 13].

*Typical design for a streak camera. Readapted from reference [8].*

*Illustration for the generation of TA signal by fs-laser pulses.*

*Excited-State Dynamics of Organic Dyes in Solar Cells DOI: http://dx.doi.org/10.5772/intechopen.94132*

Time-resolved transient emission techniques are more versatile to follow the charge dynamics in general for the charge dynamics for dyes in DSSCs. To be able following the emission spectral information along with the emission lifetimes of the studied dyes, one commonly uses time-resolved emission streak camera, **Figure 5** shows the basic components for measuring emission using streak camera. The main advantage of using streak camera is the ease of utilizing it in comparison with other techniques such as fs-TA. Using emission streak camera, one needs only one laser source to excite the sample, then the emitted photons are collected and directed inside the streak camera, in which the photons can be spatially and temporally separated, resulting of a 2D-image that contain information about the time and

*Excited-State Dynamics of Organic Dyes in Solar Cells DOI: http://dx.doi.org/10.5772/intechopen.94132*

**Figure 4.** *Illustration for the generation of TA signal by fs-laser pulses.*
