Abstract
The presence of specific chemical additives in the redox electrolyte results in an efficient increase of the photovoltaic performance of dye-sensitized solar cells (DSCs). The most effective additives are 4-tert-butylpyridine (TBP), N-methylbenzimidazole (NMBI) and guanidinium thiocyanate (GuNCS) that are adsorbed onto the photoelectrode/electrolyte interface, thus shifting the semiconductor's conduction band edge and preventing recombination with triiodides. In a comparative work, we investigated in detail the action of TBP and NMBI additives in ionic liquid-based redox electrolytes with varying iodine concentrations, in order to extract the optimum additive/I2 ratio for each system. Different optimum additive/I2 ratios were determined for TBP and NMBI, despite the fact that both generally work in a similar way. Further addition of GuNCS in the optimized electrolytic media causes significant synergistic effects, the action of GuNCS being strongly influenced by the nature of the corresponding co-additive. Under the best operation conditions, power conversion efficiencies as high as 8% were obtained.
Highlights
Current efficiencies of dye-sensitized solar cells (DSCs) can compete with the ones gained by established photovoltaic systems such as monocrystalline Si [1]
When TBP was added in the 1-methyl-3-propylimidazolium iodide (PMII) redox electrolyte (the J-V characteristic curves are shown in Figure S2 (Additional file 2), while Table S2 in Additional file 2 summarizes the photovoltaic parameters in detail), the Voc of the corresponding cells was increased under all circumstances (Figure 1a)
We have studied and compared the influence of additives (TBP, NMBI and guanidinium thiocyanate (GuNCS)) in lithiumfree ionic liquid-based electrolytes containing the I-/I3- redox couple dissolved in propylene carbonate
Summary
Current efficiencies of dye-sensitized solar cells (DSCs) can compete with the ones gained by established photovoltaic systems such as monocrystalline Si [1]. Nitrogen heterocyclic compounds such as 4-tert-butylpyridine (TBP) and N-methylbenzimidazole (NMBI) are added in the electrolyte to improve the open-circuit potential (Voc) [6,7] while guanidinium thiocyanate (GuNCS) was found to increase both Voc and the short-circuit photocurrent (Jsc) [8,9]. In this work, we comparatively studied the effects of TBP and NMBI additives in redox electrolytes of varied iodine concentration. When optimum TBP/I2 and NMBI/I2 concentration ratios were determined, the effects of the addition of GuNCS in these systems were further investigated. When the optimum NMBI or TBP-based electrolyte compositions (0.45 M) were determined (respectively), 0.05 M of GuNCS (Aldrich) was added in each system [16,17]. Low statistical errors (see tables) validate the repeatability of the measurements and justify the representative outcome for our analysis
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