Direct Dynamic Evidence of Charge Separation in a Dye‐Sensitized Solar Cell Obtained under Operando Conditions by Raman Spectroscopy

Abstract

Interfaces play an important role in enhancing the energy conversion performance of dye‐sensitized solar cells (DSCs). The interface effects have been studied by many techniques, but most of the studies only focused on one part of a DSC, rather than on a complete solar cell. Hence, monitoring the interface evolution of a DSC is still very challenging. Here, in situ/operando resonance Raman (RR) spectroscopic analyses were carried out to monitor the dynamics of the photovoltaic conversion processes in a DSC. We observed the creation of new species (i.e., polyiodide and iodine aggregates) in the photosensitization process. We also obtained molecular‐scale dynamic evidence that the bands from the C=C and C=N bonds of 2,2′‐bipyridyl (bpy), the S=C=N bonds of the NCS ligand, and photochemical products undergo reasonably strong intensity and frequency changes, which clearly demonstrates that they are involved in charge separation. Furthermore, RR spectroscopy can also be used to quickly evaluate the performance of DSCs.

A High-Performance Quasi-Solid-State Aqueous Zinc–Dual Halogen Battery

“…As shown in in situ Raman spectra (Figure S18) and the corresponding color plot (Figure 3c,d), a characteristic peak that emerged at ∼167 cm −1 corresponds to the higher polyiodide (i.e., I 5 − ). 36,37 The intensity of this peak increases during the voltage range of 1.20−1.50 V, confirming the I − /I 0 redox reaction (Figure 3e, bottom panel). When the voltage reaches 1.50 V, the peak begins to shift toward higher frequency, which can be attributed to the generation of [IBr 2 ] − interhalogen (∼180 cm −1 ).…”

“…In situ Raman spectroscopy and XPS were applied to investigate the carbon cloth–iodine cathode cycling in LiNO 3 -containing electrolyte. As shown in in situ Raman spectra (Figure S18) and the corresponding color plot (Figure c,d), a characteristic peak that emerged at ∼167 cm –1 corresponds to the higher polyiodide (i.e., I 5 – ). , The intensity of this peak increases during the voltage range of 1.20–1.50 V, confirming the I – /I 0 redox reaction (Figure e, bottom panel). When the voltage reaches 1.50 V, the peak begins to shift toward higher frequency, which can be attributed to the generation of [IBr 2 ] − interhalogen (∼180 cm –1 ). , In the middle panel of Figure e, such a characteristic peak suggests the co-existence of higher polyiodides and [IBr 2 ] − interhalogen.…”

Remarkable 8.3% efficiency and extended electron lifetime towards highly stable semi-transparent iodine-free DSSCs by mitigating the in-situ triiodide generation

“…It is very likely that part of the I 3 − species no longer interacted with the dye but were completely reduced to I -. The absence of polyiodides in the iodide-containing might be due to the same spontaneous reduction process encouraged by a possible functioning in over operando conditions (Voc D2I < Voc D2, Table 1) [88].…”

“…Increasing the measurement time seemed to not affect the Peak 1 and Peak 3 evolution (Fig. 3b) indicating that the I 3 − was constantly generated and regenerated as well as the polyiodides whose contribution was observed at around 170 cm -1 (peak 4) [88]. The evolution of the Peak 3/Peak 1 ratio confirmed that an equilibrium, not far from the initial state, of the I 3 − flow inside the device, was quickly established through the Grotthuss-type electron exchange mechanism [89].…”

“…A peak centered at 146 cm -1 (noted as Peak 3 in Fig. 3a) could be assigned to the N719 sensitized TiO2 [88].…”