Tuning of Conductivity and Density of States of NiO Mesoporous Films Used in p-Type DSSCs

Abstract

Nickel oxide has been used as the mesoporous electrode material for p-type dye sensitized solar cell (DSSC) for many years, but no high efficiency cells have been obtained yet. The poor results are commonly attributed to the lack of conductivity of the NiO film. In this paper we studied the electrical conduction of NiO mesoporous film with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). We used unsensitized NiO on FTO as an electrode with no dye adsorbed on the surface. Tests made with a DSSC device-like cell (FTO-Pt-I–/I3 –-NiO-FTO) showed a surprisingly high Faradaic current (20 mA/cm–2 at 1 V), proving a good electrical conductivity of mesoporous NiO. We also used lithium as dopant to improve the electrical properties of the film. The Li-doping resulted in widening the inert (not conductive) window in the CV plot. The EIS analysis clarified that this behavior is due to a strong dependence of the valence band shape and position with respect to the Li-doping concentration. Our results show that DSSC performance does not need to be limited by the conductivity of mesoporous NiO, which encourages more effort in p-type DSSC research based on this material.

The effect of Ni(CH3COO)2 post-treatment on the charge dynamics in p-type NiO dye-sensitized solar cells

“…For example, Huang et al reported that g of NiO p-DSSCs will enhance by 146 %, if the interface recombination can be artificially eliminated [11]. This serious interface recombination of p-type DSSCs is mainly attributed to two factors: firstly, the position of the NiO valence band is close to the I 3 -/I -redox potential and would cause an overlap between them [2][3][4], and secondly there are trap states placed slightly above the valence band widely that act as carrier generation-recombination centers at the NiO/ dye/electrolyte interface [12,13]. Obviously, the adjustment of suitable band energetic structure and elimination or passivation of surface trap states can provide an effective way to reduce the recombination losses in p-type DSSCs.…”

Ni Mg Mixed Metal Oxides for p-Type Dye-Sensitized Solar Cells

“…MgO/NiO samples the peak frequency of the diffusion resistance (around 5 Hz) remains unchanged as the applied potential increases, but the shift of the peak frequency of the charge transfer resistance as the applied potential increases is indicative of a faster interfacial reaction rate. 4 This decreases with increasing concentration of MgO, until it is almost negligible for the 25% wt. MgO/NiO sample.…”

“…This behavior agrees with that reported by D'Amario and co-workers. 4 As the amount of Mg in the films increases this middle peak increases in size; for 0-5% wt.…”

Developments in and prospects for photocathodic and tandem dye-sensitized solar cells

“…This suggests that as ΔGreg is reduced, so should be the driving force for recombination between the dye anion and the injected hole, furthermore, D'Amario et al recently demonstrated deep traps in NiO [179]. In spite of this and low conductivity in bulk NiO, mesoporous NiO appears to be capable of supporting high photocurrents (in the range of 20 mA/cm 2 , which is what would be required of a high performance pnDSC.…”