Wanchun Xiang

Aqueous dye-sensitized solar cell electrolytes based on the cobalt(II)/(III) tris(bipyridine) redox couple

In this study, we report the first application of a cobalt(II)/(III) tris(2,2′-bipyridine) based aqueous electrolyte in the fabrication of dye-sensitized solar cells. An improvement in short circuit current was observed by adjusting the concentration of polyethylene glycol in the aqueous electrolyte, which is attributed to better diffusion of the redox mediator within the electrolyte. Replacement of platinum with a composite ITO/platinum counter electrode material results in a further increase in energy conversion efficiency to above 5%. Electrochemical impedance measurements indicate a dramatic decrease in charge transport resistance at the interface between the counter electrode and aqueous electrolyte when ITO/Pt was used. Moreover, significantly improved device stability over previously reported water based DSCs under 1 sun illumination suggests that cobalt(II)/(III) tris(2,2′-bipyridine) is a promising redox mediator for highly efficient aqueous dye-sensitized solar cells.

Cyanomethylbenzoic Acid: An Acceptor for Donor–π–Acceptor Chromophores Used in Dye‐Sensitized Solar Cells

Sensing the sun: Incorporation of a cyanomethyl benzoic acid electron acceptor into donor-π-acceptor sensitizers for dye-sensitized-solar cell is shown to lead to devices with improved conversion efficiency when compared with more widely used cyanoacetic acid acceptor.

Controlling interfacial recombination in aqueous dye-sensitized solar cells by octadecyltrichlorosilane surface treatment.

A general and convenient strategy is proposed for enhancing photovoltaic performance of aqueous dye-sensitized solar cells (DSCs) through the surface modification of titania using an organic alkyl silane. Introduction of octadecyltrichlorosilane on the surface of dyed titania photoanode as an organic barrier layer leads to the efficient suppression of electron recombination with oxidized cobalt species by restricting access of the cobalt redox couple to the titania surface. The champion ODTS-treated aqueous DSCs (0.25 mM ODTS in hexane for 5 min) exhibit a V(oc) of 821±4 mV and J(sc) of 10.17±0.21 mA cm(-2), yielding a record PCE of 5.64±0.10%. This surface treatment thus serves as a promising post-dye strategy for improving the photovoltaic performance of other aqueous DSCs.

Introducing manganese complexes as redox mediators for dye-sensitized solar cells.

The abundance and low toxicity of manganese have led us to explore the application of manganese complexes as redox mediators for dye sensitized solar cells (DSCs), a promising solar energy conversion technology which mimics some of the key processes in photosynthesis during its operation. In this paper, we report the development of a DSC electrolyte based on the tris(acetylacetonato)manganese(iii)/(iv), [Mn(acac)3](0/1+), redox couple. PEDOT-coated FTO glass was used as a counter electrode instead of the conventionally used platinum. The influence of a number of device parameters on the DSC performance was studied, including the concentration of the reduced and oxidized mediator species, the concentration of specific additives (4-tert-butylpyridine, lithium tetrafluoroborate, and chenodeoxycholic acid) and the thickness of the TiO2 working electrode. These studies were carried out with a new donor-π-acceptor sensitizer K4. Maximum energy conversion efficiencies of 3.8% at simulated one Sun irradiation (AM 1.5 G; 1000 W m(-2)) with an open circuit voltage (VOC) of 765 mV, a short-circuit current (JSC) of 7.8 mA cm(-2) and a fill factor (FF) of 0.72 were obtained. Application of the commercially available MK2 and N719 sensitizers resulted in an energy conversion efficiency of 4.4% with a VOC of 733 mV and a JSC of 8.6 mA cm(-2) for MK2 and a VOC of 771 mV and a JSC of 7.9 mA cm(-2) for N719. Both dyes exhibit higher incident photon to current conversion efficiencies (IPCEs) than K4.

Titania nanobundle networks as dye-sensitized solar cell photoanodes

Quasi-one-dimensional (1D) titania nanobundles were synthesized via a hydrothermal method and used to print random network nanostructured films. These films are shown to be ideally suited for application as photoanodes in dye-sensitized solar cells (DSCs) as they have a higher porosity compared to the traditional 1D nanostructured TiO2 materials. Devices constructed using the N719 dye and iodide/triiodide as the redox mediator in the electrolyte yielded energy conversion efficiencies (η = 6.1 ± 0.2%), which were marginally lower than for devices made with the commonly used P25 titania films (η = 6.3 ± 0.1%) under one sun simulated solar radiation. Application of an electrolyte based on the [Co(bpy)3](2+/3+) redox couple and the MK2 organic sensitizer resulted in higher efficiencies (η = 7.70 ± 0.1%) than for the P25 devices (η = 6.3 ± 0.3%). Each performance parameter (short circuit current density, open circuit voltage and fill factor) was higher for the TiO2 nanobundle devices than those for the P25-based devices. The results of electrochemical impedance spectroscopy (EIS), intensity-modulated photovoltage spectroscopy (IMVS), and dye-loading measurements indicated that the better performance of TiO2 nanobundle devices with cobalt electrolytes correlates with higher porosity, relatively fast electron transport and more efficient suppression of electron recombination. A faster rate of diffusion of the cobalt complexes through the highly porous TiO2 nanobundle network is proposed to contribute to the enhanced device efficiency.

Aqueous p-type dye-sensitized solar cells based on a tris(1,2-diaminoethane)cobalt(II)/(III) redox mediator

For the first time, we report the assembly of p-type dye-sensitized solar cells (pDSCs) based on an aqueous electrolyte containing a tris(1,2-diaminoethane)cobalt(II/III) ([Co(en)3]2+/3+) redox couple. With exception of devices made with pH 8.15 electrolytes (η = 1.13%) constant energy conversion efficiencies close to 1.5% were achieved with all other electrolytes under simulated one sun illumination (AM 1.5 G), with the best cell achieving an efficiency of 1.6%. Even higher efficiencies (≥1.9%) were achieved at a lower light intensity indicating that mass transport may be limiting performance at higher light intensities. The drop in VOC with increasing pH is compensated by improvements in the short circuit current and fill factor. Notably, the efficiencies reported here for electrolytes with pH > 9 are higher than those reported for the corresponding devices made with an organic electrolyte based on the same redox mediator.