Effects of Aqueous Electrolyte, Active Layer Thickness and Bias Irradiation on Charge Transfer Rates in Solar Cells Sensitized with Top Efficient Carbazole Dyes

Abstract

The photovoltaic performance and electron-transfer dynamics from femtoseconds to milliseconds are explored for very efficient carbazole sensitizers applied in solar cells, including the champion dye ADEKA-1. The photocurrent in the novel, environmentally friendly aqueous electrolyte is about 40% of that in the standard acetonitrile one, both based on cobalt complexes as a redox pair. The drop in the photocurrent is found to be correlated with increased electron recombination between sensitized titania particles and dyes, taking place with a time constant of several hundreds of picoseconds. Electron injection and recombination between titania and dye are slowed down under the presence of water (about 10 times) and with additional 1 sun bias irradiation (about 2 times). These effects are interpreted as due to reduced electronic coupling between the electron donors (dyes) and acceptor framework (titania). Moreover, a decrease in the relative photocurrent, photovoltage, and fill factor of the cells with increasing thickness of titania layers are observed. The obtained results should be relevant for the optimization of solar cells with a large class of organic sensitizers, especially when looking for nontoxic configurations and determining true charge transfer rates under operating solar cell conditions.

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

“…Our interpretation of the transient absorption measurements collected for Y123 sensitized solar cells is provided in the previous part of this paper. On the other hand, MK2 dye was extensively studied by our group and we based our interpretation on the previous reports [41][42][43][44][45]. Namely, we attributed the two faster (3-4 ps and 30-35 ps, black and red lines in Figure 4C,D) components to electron injection process.…”

“…Besides the Y123 based cells, we used well-described systems based on carbazole MK2 dye (Supplementary Scheme S1B), extensively studied by our group for the last few years [41][42][43][44][45]. Both dyes were studied in combination with [Co(bpy) 3 ](B(CN) 4 ) 2/3 (bpy = 2,2 -bipyridine) [9] and [Cu(tmby) 2 ](TFSI) 1/2 (tmby = 4,4 ,6,6 tetramethyl-2,2bipyridine, TFSI = bis(trifluoromethane)sulfonamide) [15], providing new insights into the dynamics of electron separation and recombination in Y123 and their impact on photocurrent generation.…”

Progress on Electrolytes Development in Dye-Sensitized Solar Cells

“…The efficiency record for a 100% water-based DSSC is 5.97%, as obtained by Lin et al in 2015, in combination with a metal-free organic dye (EO3) and TEMPO/iodide electrolyte [121]. Most of the studies in this research area present energy conversion efficiency usually below 3% device despite this impressive efficiency presented by Lin for an aqueous-based DSSC [116,117,118,119,120]. Accordingly, further improvements on this aqueous system, as well for the other components of DSSC, are necessary.…”

“…However, in recent studies, water has emerged as a promising solvent to prepare aqueous-based electrolytes for DSSC [116,117,118,119]. Water being used as the main solvent presents some advantages, such as producing a low cost, nontoxic, non-flammable, and an eco-friendly photovoltaic devices [116,117,118,119,120]. The efficiency record for a 100% water-based DSSC is 5.97%, as obtained by Lin et al in 2015, in combination with a metal-free organic dye (EO3) and TEMPO/iodide electrolyte [121].…”

Solar electricity and fuel production with perylene monoimide dye-sensitised TiO2in water

“…However, increasing attention to fully green processes has driven growing efforts towards aqueous DSCs, notably targeting optimised electrolytes ( e.g. redox mediator and additives), improved surface wettability or water-tolerant dyes 15–23. DSP for water splitting is naturally inclined towards an aqueous solution as water can act as both solvent and substrate for H 2 and O 2 evolution 4…”