Effect of solvent and additives on the open-circuit voltage of ZnO-based dye-sensitized solar cells: a combined theoretical and experimental study

Abstract

We have investigated the role of electrolyte composition, in terms of solvent and additive, on the open-circuit voltage (V(oc)) of ZnO-based dye-sensitized solar cells (DSSCs) using a combined experimental and theoretical approach. Calculations based on density functional theory (DFT) have been performed in order to describe the geometries and adsorption energies of various adsorbed solvents (nitromethane, acetonitrile and dimethylformamide) and p-tert-butylpyridine (TBP) (modeled by methylpyridine) on the ZnO (100) surface using a periodic approach. The densities of states (DOS) have been calculated and the energy position of the conduction band edge (CBE) has been evaluated for the different molecules adsorbed. The effect of the electrolyte composition on the standard redox potential of the iodide/triiodide redox couple has been experimentally determined. These two data values (CBE and standard redox potential) allowed us to determine the dependence of V(oc) on the electrolyte composition. The variations determined using this method were in good agreement with the measured V(oc) for cells made of electrodeposited ZnO films sensitized using D149 (indoline) dye. As in the case of TiO(2)-based cells, a correlation of V(oc) with the donor number of the adsorbed species was found. The present study clearly points out that both the CBE energy and the redox potential variation are important for explaining the experimentally observed changes in the V(oc) of DSSCs.

Brookite TiO2 Nanoparticle Films for Dye‐Sensitized Solar Cells

“…Better V oc values can be due to a higher energy of the conduction band of the doped brookite than that of pure brookite and/or to a reduced recombination in the case of lanthanum cells. [32] Lower dark currents curves in Figure 4 b are in good agreement with higher V oc values. We show below that the electron lifetimes are shorter in the lanthanum-doped samples, therefore, the higher V oc value is most probably due to a higher conduction band energy.…”

Metal Complexes as Redox Shuttles in Dye-Sensitized Solar Cells Based on Electrodeposited ZnO: Tuning Recombination Kinetics and Conduction Band Energy

“…Interestingly, when TBP is used in I − /I 3 − -based cells, a rapid dye desorption at a concentration of 0.5 M is observed much more drastic than in the present experiment with Co(bpy) 3 . 29 Since it is known that alkaline molecules tend to dissolve the acidic dye molecules from the ZnO surface, this indicates that the Co(bpy) 3 -based electrolyte represents a much more acidic environment than the I − /I 3 − -based electrolyte. This is supporting the observation of a largely downward shifted conduction band edge in ZnO-based DSSCs employing the Co(bpy) 3 redox electrolyte if no alkaline molecules are added.…”

Charge collection properties of dye-sensitized solar cells based on 1-dimensional TiO2 porous nanostructures and ionic-liquid electrolytes

“…It has to be noted that more standard materials such as TiO 2 paste from Solaronix was found not to perform well with the organic dye and the ionic-liquid electrolyte utilized here. Incompatibilities between organic dyes and ionic-liquid electrolytes have been reported in the literature a number of times [39,50].…”