Photoelectrochemical Response of DSSCs Under Prolonged Reverse Bias and Conduction Band Lowering in Ru‐Complex‐Sensitized TiO₂

Abstract

TiO2‐based dye‐sensitized solar cells (DSSCs) sensitized with the Ru‐dyes N719 and Z907, are subjected to prolonged reverse bias (RB) by imposing a constant current density of 25 mA cm−2 for up to 1000 h. The temporal changes of the DSSCs during the aging process are followed by the periodical recording of current–voltage curves, electrochemical impedance spectra, charge extraction measurements, and photovoltage decays at the various stages of cell aging. Beside the expected decrease in the concentration of ${{\rm{I}}_3^ - }$ during RB aging, the measurements show a surprising shift of the conduction band edge toward lower energies and a concomitant slowing down of the recombination process with the electrolyte for both DSSCs. This leads to a noticeable improvement in the energy conversion efficiency under low illumination conditions. These unexpected results are discussed on the basis of recent literature reports and attributed tentatively to the adsorption of H+ ions, which are produced during the RB aging, onto the TiO2 surface.

Effect of Alkyl Chain Length on the Sensitizing Action of Substituted Non‐Symmetric Squaraines for p‐Type Dye‐Sensitized Solar Cells

“…This finding is consistent with the fact that a positive increase of E appl with respect to V OC represents a forward bias of the cell with consequent increase of the number of injected charges with respect to the situation of open circuit. Such an effect is analogous to the one provoked by the increase of the intensity of the light irradiating the cell . The addition of injected charge carriers with respect to the situation at V OC brings about a decrease of the resistive terms associated to charge transport through the NiO skeleton ( R t ) and to the recombination phenomena ( R rec ), the latter event being combined to the kinetic equation {6} ( vide supra ).…”

NiO/ZrO2 nanocomposites as photocathodes of tandem DSCs with higher photoconversion efficiency with respect to parent single-photoelectrode p-DSCs

“…conventional I-based and Co-based electrolytes) lead to much lower FF (< 0.50). Indeed, the limits of p-DSCs are evidenced through the recognition that p-DSCs generally display lower values of fill factor (FF) [37][38][39] in comparison to n-DSCs 40,41 and other junction-based photovoltaic devices. [42][43][44][45] One should note that a relatively low FF is not inherently related to pDSCs (or NiO), but its value is rather ruled by the built-in potential of the device, i.e.…”

Cobalt Sulfide as Counter Electrode in p-Type Dye-Sensitized Solar Cells

“…In such conditions, CoS will result generally reverse‐biased (RB) when the cell is exposed to light. Adverse reactions in RB conditions have been recently reported in previous studies of n ‐type DSC when I − /I 3 − as redox mediator . However, the observed little differences in V oc do not affect significantly the overall efficiency of the two differently configured p ‐DSCs (Table ).…”