Interface Modification and Exceptionally Fast Regeneration in Copper Mediated Solar Cells Sensitized with Indoline Dyes

Abstract

The photovoltaic performance of solar cells sensitized with indoline D205 dye and its new derivative comprising an alkoxysilyl anchoring unit (D205Si) in the [Cu(tmby) 2 ](TFSI) 2/1 (tmby = 4,4′,6,6′tetramethyl-2,2′-bipyridine, TFSI = bis(trifluoromethane)sulfonimide) redox couple mediated systems was studied in the presence of various titania/dye/electrolyte interface modifications. Cucurbit[7]uril (CB7) was employed to encapsulate dye molecules, creating an electronically insulating layer, suppressing electron interception by redox mediator, and leading to the increase in the electron lifetime in the titania conduction band. For example, the electron lifetime increased from 2.2 to 6.5 ms upon CB7 encapsulation of D205 cells at 0.9 V voltage. Further, molecular multicapping was optimized to minimize dye desorption and prevent electron recombination. As a result, photovoltaic performance was found to be enhanced by the interface modifications in most cases, especially when applied to the alkoxysilyl anchoring derivative. The charge transfer processes (dye regeneration, titania-dye and titania-redox mediator recombination) in the above-mentioned system and in the reference [Co(bpy) 3 ](TFSI) 3/2 (bpy = 2,2′-bipyridine) redox couple mediated systems were investigated by means of small light perturbation electron lifetime measurements, electrochemical impedance spectroscopy, and nanosecond and femtosecond transient absorption spectroscopies. Indoline dyes were also found to be outstandingly fast regenerated by the Cu-based mediator (time constant shorter than 100 ns), which may open new opportunities for sensitizer improvements.

Copper Complexes as Alternative Redox Mediators in Dye-Sensitized Solar Cells

“…The widely used BP2 redox mediators were coupled, in 2020, by Glinka, Ziółek et al with other organic dyes, such as the indoline-based sensitizers D205 and D205Si [ 49 ]; the latter compound presented a silyl-anchoring group instead of the carboxylic moiety of the former one ( Figure 5 ).…”

Complexity of Electron Injection Dynamics and Light Soaking Effects in Efficient Dyes for Modern DSSC

“…In some indicated control cells, the electrolytes without TBP were used. Platinized counter electrodes for Co-based and poly-3,4 ethylenedioxytiophene (PEDOT) coated ones for Cu-based electrolyte mediated solar cells were prepared according to methods specified elsewhere [46].…”

“…Supplementary Table S1 collects the time constants for all components at three excitation wavelengths. The wavelength-dependent amplitude of the second component contains also a negative signal or an indentation in the positive signal in the range between 700 nm and 850 nm, which can be assigned to the stimulated emission and/or to building up of the oxidized state population (the rise of its transient absorption can be visible as the second peak in the photoinduced absorption measurements [46]). For the samples containing a cobalt redox mediator, the positive band in the short wavelength part of the spectra, may be distorted by the residuum of the stimulated emission from hot (Franck-Condon) S1 state of the dye.…”

“…For the samples containing a cobalt redox mediator, the positive band in the short wavelength part of the spectra, may be distorted by the residuum of the stimulated emission from hot (Franck-Condon) S1 state of the dye. Small shifts (~10 nm) between the spectra recorded in Co and Cu based electrolytes, observed, e.g., in the positions of bleach bands in Figure 1, the positions of the absorption maxima in Figure 2, and IPCE spectra in Supplementary Figure S1B should be The wavelength-dependent amplitude of the second component contains also a negative signal or an indentation in the positive signal in the range between 700 nm and 850 nm, which can be assigned to the stimulated emission and/or to building up of the oxidized state population (the rise of its transient absorption can be visible as the second peak in the photoinduced absorption measurements [46]). For the samples containing a cobalt redox mediator, the positive band in the short wavelength part of the spectra, may be distorted by the residuum of the stimulated emission from hot (Franck-Condon) S 1 state of the dye.…”

“…However, decent V OC values matching the best reported, indicate good quality of prepared samples. To compare samples of different light harvesting efficiency in terms of the photocurrent generation efficiency, we calculated the total absorbed photon to current efficiency (Total APCE), the parameter which is a short circuit photocurrent density corrected for the number of absorbed photons [46]. It should be also noted that our Total APCE values are quite close to the best IPCE values reported for the optimized cells (~80%), which means that the conclusions regarding electron injection dynamics should also be valid for the best performing cells with the scattering layer.…”