Fuwei Zhuge

Solution-derived 40 µm vertically aligned ZnO nanowire arrays as photoelectrodes in dye-sensitized solar cells

Well-aligned ZnO nanowire arrays with a long length of more than 40 microm were prepared successfully by using the polyethylenimine (PEI)-assisted preheating hydrothermal method (PAPHT). Several important synthetic parameters such as PEI content, growth time, preheating time and zinc salt concentration were found to determine the growth of ultralong ZnO nanowire arrays, including length, diameter, density and alignment degree. The photoluminescence (PL) spectrum of as-grown ultralong ZnO nanowire arrays revealed a UV emission and a yellow emission, which was attributed to the absorbed hydroxyl group based on the peak shift after annealing in various atmospheres. The performance of dye-sensitized solar cells (DSSCs) increased with increasing length of ZnO nanowire arrays, which was mainly ascribed to the aggrandized photocurrent and reduced recombination loss according to electrochemical impedance spectroscopy (EIS). A maximum efficiency of 1.3% for a cell with a short-circuit current density (J(sc)) = 4.26 mA cm(2), open-circuit voltage (V(oc)) = 0.69 V and (fill factor) FF = 0.42 was achieved with a length of 40 microm.

Toward Hierarchical TiO2 Nanotube Arrays for Efficient Dye‐Sensitized Solar Cells

Dye-sensitized solar cells (DSCs) have been considered as one of the low cost alternatives for conventional silicon solar cells since the fi rst application of transparent TiO 2 nanocrystalline fi lms in 1990s. [ 1 ] Light-harvesting ability and internal carrier collection effi ciency via the sensitized photoanode constitute the key factors that determine the performances of DSCs. Effi ciencies exceeding 11% have already been achieved in laboratories with the sensitizers of N719 and C101, [ 2 ] whereas the overall performances are still lower than the predicted values due to poor utilization of near infrared photons and recombination losses in the random network of TiO 2 nanocrystallines. [ 3 ]

A facile route to aligned TiO2 nanotube arrays on transparent conducting oxide substrates for dye-sensitized solar cells

TiO2 nanotube arrays (NTAs) on transparent conducting oxides (TCO) have attracted great attention due to the potential application in dye-sensitized solar cells (DSCs). Here, we introduce the template-assisted process for direct fabrication of aligned TiO2 NTAs on TCO substrates, involving layer-by-layer adsorption and reaction (LBL-AR) assembled TiO2 coating on ZnO nanorods (NR). Key factors of the fabrication process on the microstructures of TiO2 NTAs are analyzed, and the geometry effects of TiO2 NTAs on the performance and electron transport properties of DSCs are investigated by using electrochemical impedance spectra (EIS). An efficiency of 4.25% (under AM1.5 irradiation, 100 mW cm−2) is obtained from N719 sensitized 20 μm thick TiO2 NTAs with a wall thickness of 20 nm, with Jsc = 8.2 mA cm−2, Voc = 0.81 V and FF = 63%.

Advantages of using Ti-mesh type electrodes for flexible dye-sensitized solar cells

We used Ti meshes for both the photoanodes and counter electrodes of dye-sensitized solar cells (DSSCs) to improve the flexibility and conductivity of the electrodes. These mesh type electrodes showed good transparency and high bendability when subjected to an external force. We demonstrated the advantages of cells using such electrodes compared to traditional transparent conducting oxide based electrodes and back side illuminated DSSCs, such as low sheet resistance, elevated photo-induced current and enhanced sunlight utilization. Nanotube layers of different thicknesses were investigated to determine their effect on the photovoltaic parameters of the cell. The overall efficiency of the best cells was approximately 5.3% under standard air mass 1.5 global (AM 1.5 G) solar conditions. Furthermore, the DSSCs showed an efficiency of approximately 3.15% due to the all Ti-mesh type electrodes even after illumination from the back side.

ZnO NANOPOROUS DISK–TiO2 NANOPARTICLE HYBRID FILM ELECTRODE FOR DYE-SENSITIZED SOLAR CELLS

Micron-sized ZnO disks with nanosized pores were synthesized by decomposing the solution-grown layered zinc compound ZnCl2 · [Zn(OH)2]4 · H2O (ZCOH) at 500°C. ZnO–TiO2 hybrid film electrodes were prepared by the doctor-blade method, adding ZnO disk powder to the TiO2 slurry. The crystallinity, microstructure and optical properties of the ZCOH, ZnO nanoporous disk, and the resulting hybrid films, were investigated. Electrochemical impedance spectroscopy and the photocurrent density–voltage curve were employed to characterize the interfacial electron-transporting properties and photoelectrochemical performance of dye-sensitized solar cells (DSCs) using the ZnO–TiO2 hybrid electrode. Results indicated that the incorporation of a small amount of ZnO disks into the TiO2 film (less than 1%) can roughen the surface structure, reduce the film thickness, enhance the light scattering in the visible and infrared bands, and increase the interfacial charge transport rate. Hybrid cells showed efficiency improvements of 145% and 109% with the concentrations of ZnO of 0.5% and 1% in the hybrid film respectively, compared with the traditional TiO2 cell, with a significant increase in the short-currency density and the fill factor. Although the 2.7% efficiency (Jsc = 4.0 mA ° cm-2; Voc = 0.74 was not high with the 0.5% ZnO disk incorporated, this work highlighted the potential improvement that novel ZnO nanostructures in hybrid DSCs can achieve.

Coaxial multi-shelled TiO2 nanotube arrays for dye sensitized solar cells

The performance of one-dimensional (1D) TiO2 nanotube based dye-sensitized solar cells (DSCs) was limited by the insufficient surface area of TiO2 nanotubes. To solve this issue, coaxial multiple-shelled TiO2 nanotube arrays were successfully synthesized on the transparent conductive oxide (TCO) substrates by using improved ZnO nanorod template assisted layer by layer absorption and reaction (LbL-AR) technique. To fabricate tube-in-tube nanostructures, LbL-AR TiO2 coatings were successively deposited on the exterior walls of the ZnO nanowires and the sacrificial sol–gel ZnO spacers, which were removed together by selective etching to form the hollow tubal structures. The performance of dye-sensitized solar cells (DSCs) increases with increasing the shell number of multi-shelled TiO2 nanotube photoanodes, attributed to the increase of the surface area, which was confirmed by N2 adsorption-desorption isotherms and the dye-loading capacities. A maximum efficiency of 6.2% was achieved for a quintuple shelled TiO2 nanotube photoanode with a short-circuit current density (Jsc) = 15 mA cm2, open-circuit voltage (Voc) = 0.73 V and fill factor (FF) = 0.57.

TiO2 nanorod arrays functionalized with In2S3 shell layer by a low-cost route for solar energy conversion.

We report the fabrication and characterization of a TiO(2)-In(2)S(3) core-shell nanorod array structure for application of semiconductor-sensitized solar cells. Hydrothermally synthesized TiO(2) nanorod arrays on FTO glass substrates are functionalized with a uniform In(2)S(3) shell layer by using the successive ion layer adsorption and reaction (SILAR) method. This low-cost technique promotes a uniform deposition of In(2)S(3) nanoshells on the surface of TiO(2) nanorods, thus forming an intact interface between the In(2)S(3) shell and TiO(2) core. Results show that the thickness of In(2)S(3) shell layers as well as the visible light absorption threshold can be effectively controlled by varying the coating cycles during the SILAR process. The best reproducible performance of the sandwich solar cell using the TiO(2)-In(2)S(3) core-shell nanorod arrays as photoelectrodes was obtained after 30 SILAR cycles, exhibiting a short-circuit current (I(sc)) of 2.40 mA cm(-2), an open-circuit voltage (V(oc)) of 0.56 V, a fill factor (ff) of 0.40 and a conversion efficiency (η) of 0.54%, respectively. These results demonstrate a feasible and controllable route towards In(2)S(3) coating on a highly structured substrate and a proof of concept that such TiO(2)-In(2)S(3) core-shell architectures are novel and promising photoelectrodes in nanostructured solar cells.