An electrolyte based on the tris(acetylacetonato)iron(III)/(II) redox couple ([Fe(acac)3](0/1-)) was developed for p-type dye-sensitized solar cells (DSSCs). Introduction of a NiO blocking layer on the working electrode and the use of chenodeoxycholic acid in the electrolyte enhanced device performance by improving the photocurrent. Devices containing [Fe(acac)3](0/1-) and a perylene-thiophene-triphenylamine sensitizer (PMI-6T-TPA) have the highest reported short-circuit current (J(SC)=7.65 mA cm(-2)), and energy conversion efficiency (2.51%) for p-type DSSCs coupled with a fill factor of 0.51 and an open-circuit voltage V(OC)=645 mV. Measurement of the kinetics of dye regeneration by the redox mediator revealed that the process is diffusion limited as the dye-regeneration rate constant (1.7×10(8) M(-1) s(-1)) is very close to the maximum theoretical rate constant of 3.3×10(8) M(-1) s(-1). Consequently, a very high dye-regeneration yield (>99%) could be calculated for these devices.
Indium tin oxide (ITO) is a well-known n-type degenerate semiconductor with a wide variety of electronic and optoelectronic applications. Herein ITO is utilized as a photocathode material in p-type dye-sensitized solar cells in place of the commonly applied and highly colored nickel oxide (NiO) semiconductor. The application of mesoporous ITO photocathodes, [Fe(acac) 3 ] 0/ − as a redox mediator and a new organic dye afforded an impressive energy conversion efficiency of 1.96 ± 0.12%. Comparative transient absorption spectroscopic studies indicated that the recombination rate at the ITO-electrolyte interface is two orders of magnitude faster than that of NiO. Analysis of the operation mechanism of the ITO-based devices with ultraviolet photon spectroscopy and photoelectron spectroscopy in air showed that ITO exhibits a significant local density of states arising below − 4.8 eV, which enables electron transfer to occur from the ITO to the excited dye, thus giving rise to the sustained photocathodic current. NPG Asia Materials (2016) 8, e305; doi:10.1038/am.2016.89; published online 9 September 2016 INTRODUCTION Transparent conducting oxides have been extensively used in optoelectronic applications. 1-3 One common transparent conducting oxide is indium tin oxide (ITO). ITO is a well-known n-type degenerate semiconductor 4 with an optical band gap of 3.5-4.3 eV 5 and has a high transmission in the near infrared and visible regions of the electromagnetic spectrum. Owing to their high optical transparency, good electrical conductivity, chemical inertness, hardness and excellent substrate adherence, 6-8 ITO thin films are applied in flat panel displays, antistatic coatings, solar cells, camera lenses and architectural glazing. 9-12 Additionally, high-surface-area mesoporous ITO films have been used as sensors for gases, such as ammonia, nitric oxide, ethanol and methanol. [13][14][15][16] Moreover, ITO films and ITO/TiO 2 core-shell structures have been utilized as photoanodes in both dye-sensitized solar cells (DSCs) and water oxidation devices. [17][18][19][20] A recent spectroscopic investigation into the charge transfer dynamics of dye-coated ITO films revealed that ITO can both accept and donate electrons during photoinduced charge transfer. 21,22 By exploiting the ambivalent property of this degenerate n-type semiconductor, we have developed an efficient p-type DSC (p-DSC)
Photocatalysis is a process of clean technology where solar energy is converted into useful chemical reactions. There are confronted challenges and limitations when claiming the most efficient TiO 2 photocatalytic activity. Scientists tend to break through the barriers of TiO 2 photocatalysis by implementing different modification strategies for pure TiO 2 in order to eliminate the encountered limitations and thereby enhance the efficiency for further development of photocatalytic applications. Charge carrier recombination is one of the major limitations in the photocatalytic process. Doping incorporated with metals and nonmetals owns the capacity to subdue the recombination of photogenerated electrons and holes by ensuring charge carrier separation. At the same time, this could enhance the capturing of photoenergy by narrowing the band gap of TiO 2 . Dye sensitization is another branch of possible modification of TiO 2 photocatalysis that is implemented in solar electricity generation, photocatalytic water splitting, and pollutant degradation. It assists in reduction of transparency in the visible range and obtaining a longer electron lifetime by efficient charge separation. Attention is given to the application of TiO 2 photocatalysis based on environmental decontamination, biocidal applications, and energybased applications. Hence, TiO 2 photocatalysis plays a crucial role in reaching higher technological development while maintaining a balance with environmental sustainability.
Third generation photovoltaics are based on the concept of providing high conversion efficiencies with low device production costs. As such, second generation concepts, such as Dye-sensitized Solar Cells (DSCs), serve as a good starting point for the development of these new devices. Tandem DSC devices are one example of such a concept, and can be constructed using two photoactive electrodes (one photoanode and one photocathode) inside the one cavity, increasing the theoretical efficiency limit by around 50% as compared to the conventional design. As there has been substantial effort devoted to the development of ntype DSCs, the focus of researchers investigating tandem DSCs has been to create high performance p-type systems, which operate by an analogous, but inverted, mechanism to n-type DSCs.
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.
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