Charge Transfer and Performance Enhancement of Dye-Sensitized Solar Cells by Utilization of a Tandem Structure

Abstract

For increasing the light-harvesting ability of dye-sensitized solar cells (DSSCs), thick TiO 2 films were always utilized. However, a thicker TiO 2 film also triggers a higher charge-transfer resistance. To solve the contrary effects of film thickness on the light harvest and charge transfer, a tandem-structured cell constructed by two sub-DSSCs is proposed. By using a high transparent Pt counter electrode, the light unabsorbed by the top cell can transmit trough and be utilized by the bottom cell. The performances of the tandem cells are evaluated using N719sensitized TiO 2 photoelectrodes and the thickness effects of top and bottom cells are studied. The experimental results show that the tandem structure can significantly improve the conversion efficiency of DSSCs. For the single cells studied in this work, the highest efficiency is 9.3%, achieved by a cell with 12-μm main layer and 4-μm scattering layer. For the tandem cells, the best performance appears at the structure with 12-μm top cell and 8-μm bottom cell (12/8), and the efficiency achieved is 9.54% in the absence of scattering layer. Therefore, the effect of the 8-μm bottom cell in the tandem structure is more significant, in comparison with that of the 4-μm scattering layer, on enhancing the cell performance. Furthermore, if a scattering-layer effect is also applied on the bottom cell of the 12/8 tandem structure, the efficiency can further be improved to 10.16%. If the powers of top and bottom cells are outputted individually, the overall efficiency achieved by the tandem cell is 11.6%, which is more than 2% higher than that obtained by the single cell.

Plant Uptake-Assisted Round-the-Clock Photocatalysis for Complete Purification of Aquaculture Wastewater Using Sunlight

“…Thus, the 1.0%-Bi 2 O 3 /TiO 2 -y-500 film exhibited enhanced activity with the increasing number of coatings in photocatalytic degradation of RhB owing to the increase of film thicknesses and smoothing degree of the top surface, which promoted the light harvesting. 41,42 At five coating cycles, the photocatalytic activity reached maximum. A further increase in the number of coatings only increased the film thickness, which could not affect the photocatalytic activity since the Bi 2 O 3 /TiO 2 inside deep layer could not make contact with either the irradiation light or the reactants.…”

Whispering Gallery Mode Assisted Enhancement in the Power Conversion Efficiency of DSSC and QDSSC Devices Using TiO2 Microsphere Photoanodes

“…30 Thus, essential factors that influence PCE include efficient light absorption and charge transfer ability. 31,32 Reducing the specular reflection of light through antireflection coating and texturing the surface to increase diffuse reflection, which result in multiple scattering and hence lead to higher absorption, have been employed to enhance the harvesting of light. 33,34 Alternatively, the light trapping schemes such as whispering gallery modes (WGM) in oxide materials are found to be an efficient way to improve light harvesting.…”

“…However, the type of scattering that prevails in these microstructures resulting in higher PCE is not discussed. − Other factors that limit the PCE in solar cell include the energy loss due to charge recombination. , At the interface of the nanoparticle boundaries, the charge carriers easily get trapped resulting in the decrease of mobility and carrier lifetime . Thus, essential factors that influence PCE include efficient light absorption and charge transfer ability. , …”

Novel coumarin sensitizers based on 2-(thiophen-2-yl)thiazole π-bridge for dye-sensitized solar cells

“…The most famous Ru(II) complexes are bis(tetrabutylammonium)-cis-di(thiocyanato)bis(4,4′-dicarboxy-2,2′-bipyridine)ruthenium(II) (N719 dye) and trithiocyanato-(4,4′,4″-tricarboxy-2,2′:6′,2″-terpyridine)ruthenium(II) (black dye), achieving a high photoelectric conversion yield (η) of >11% under AM 1.5 G irradiation. 9,10 However, Ru(II) complexes suffer the disadvantages of the rarity of ruthenium metal in the earth's crust, tricky synthesis, and purification steps. Therefore, metal-free organic sensitizing dyes have attracted great attention for their large diversity in molecular structure, simple preparation, and purification processes with lower cost.…”