Yandong Duan

Phenothiazine–triphenylamine based organic dyes containing various conjugated linkers for efficient dye-sensitized solar cells

In order to increase the electron-donating ability of the donor part of the organic dye, two phenothiazine groups, as additional electron donors, were introduced into a triphenylamine unit to form a starburst donor–donor (2D) structure in this paper. Three new organic dyes (WD-6, WD-7 and WD-8) containing this starburst 2D structure and a 2-cyanoacetic acid acceptor linked by various conjugated linkers (benzene, thiophene, and furan) have been designed, synthesized and applied in dye-sensitized solar cells (DSSCs). The introduction of a phenothiazine group with a butterfly conformation in the triphenylamine donor parts has a good influence on preventing the molecular π–π aggregation due to the starburst 2D structure of the organic dye. The conjugated linker effects on the photophysical, electrochemical and photovoltaic properties of these organic dyes were investigated in detail. The DSSCs made with these organic dyes displayed remarkable overall conversion efficiencies, ranging from 4.90–6.79% under an AM 1.5 solar condition (100 mW cm−2). The best performance was found for organic dye WD-8, in which a furan group was the conjugated linker. It displayed a short-circuit current (Jsc) of 14.43 mA cm−2, an open-circuit voltage (Voc) of 682 mV, and a fill factor (ff) of 0.69, corresponding to an overall conversion efficiency of 6.79%. The different photovoltaic behaviors of the solar cells based on these organic dyes were further elucidated by the electrochemical impedance spectroscopy.

High-Performance Plastic Platinized Counter Electrode via Photoplatinization Technique for Flexible Dye-Sensitized Solar Cells

A photoplatinization technique was proposed to deposit Pt on a thin TiO(2) layer modified indium tin oxide-coated polyethylene naphthalate (ITO/PEN) substrate at low temperature (about 50 °C after 1 h of UV irradiation) for the first time. The fabrication process includes coating and hydrolyzing the tetra-n-butyl titanate to form a TiO(2)-modified layer and the photoplatinization of the modified substrate in H(2)PtCl(6)/2-propanol precursor solution under UV irradiation. The obtained platinized electrodes were used as counter electrodes (CE) for flexible dye-sensitized solar cells (FDSCs). The well-optimized platinized electrode showed high optical transmittance, up to 76.5% between 400 and 800 nm (T(av)), and the charge transfer resistance (R(ct)) was as low as 0.66 Ω cm(2). A series of characterizations also demonstrated the outstanding chemical/electrochemical durability and mechanical stability of the platinized electrode. The FDSCs with TiO(2)/Ti photoanodes and the obtained CEs achieved a power conversion efficiency (PCE) up to 8.12% under rear-side irradiation (AM 1.5 illumination, 100 mW cm(-2)). The obtained CEs were also employed in all-plastic bifacial DSCs. When irradiated from the rear side, the bifacial FDSC yielded a PCE of 6.26%, which approached 90% that of front-side irradiation (6.97%). Our study revealed that, apart from serving as a functional layer for deposition of Pt, the thin TiO(2) layer modification on ITO/PEN substrates also played an important role in improving the transparency and the mechanical properties of the CE. The effect of the thickness of the TiO(2) layer for Pt coating on the performance of the CE was also investigated.

Influence of the antennas in starburst triphenylamine-based organic dye-sensitized solar cells: phenothiazine versus carbazole

A new starburst triphenylamine-based organic dye (WD-1) with phenothiazine units as antenna groups was designed and synthesized and the corresponding dye (WD-4) containing carbazole antennas for the purpose of comparison was also synthesized. They were successfully applied in dye-sensitized solar cells (DSSCs). The photophysical and electrochemical properties of the dyes were investigated by UV-vis spectrometry and cyclic voltammetry. Under standard global AM 1.5 solar conditions, the WD-1 sensitized solar cell gave a short circuit photocurrent density (Jsc) of 9.2 mA cm−2, an open circuit voltage (Voc) of 625 mV, a fill factor (ff) of 0.79, corresponding to an overall conversion efficiency η of 4.54%. Under the same conditions, the WD-4 sensitized cell gave a Jsc of 7.3 mA cm−2, an Voc of 603 mV, and a ff of 0.74, corresponding to an overall conversion efficiency of 3.26%. An increase in η of about 39% was obtained from WD-4 to WD-1. Our findings demonstrate that the introduction of phenothiazine units as antennas in triphenylamine-based dyes could improve photovoltaic performance compared with carbazole units as antennas in DSSCs.

Mn3O4/graphene composite as counter electrode in dye-sensitized solar cells

Mn3O4-anchored reduced graphene oxide (Mn3O4/RGO) nanocomposites have been successfully synthesized via a facile, effective, energy-saving technique. The surface morphology and structure of the Mn3O4/RGO composites were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), high resolution transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Brunauer–Emmett–Teller (BET) surface area and Barrett–Joyner–Halenda porosity (BJH). The composite material was applied as the counter electrode (CE) for dye-sensitized solar cells (DSSCs). Electrochemical impedance spectra (EIS), cyclic voltammetry (CV) and Tafel polarization measurements revealed a better electrocatalytic performance for the reduction of triiodide in Mn3O4/RGO based DSSCs, compared with the devices with reduced graphene oxide (RGO) CEs. The Mn3O4/RGO improves the fill factor by 56% and the power conversion efficiency of this kind of DSSC reaches 5.90%, which is much higher than the DSSC assembled from RGO CEs. A Pt counter electrode as a reference was also tested.

Novel organic sensitizers containing dithiafulvenyl units as additional donors for efficient dye-sensitized solar cells

In order to increase the electron-donating ability of the donor part of the organic dye, the dithiafulvenyl (DTF) group as an additional electron donor is introduced into a triphenylamine (TPA) unit to form a donor–donor (2D) structure in this paper. Two new organic dyes WD9 (one 2-cyanoacetic acid as an electron acceptor) and WD11 (two 2-cyanoacetic acids as electron acceptors) containing this DTF–TPA 2D structure are designed, synthesized and applied in dye-sensitized solar cells (DSSCs). It is found that the double donor structures (DTF–TPA) not only contribute to enhancement of the electron-donating ability, but also inhibit aggregation between dye molecules and prevent I3− in the electrolyte from recombining with injected electrons in TiO2. Under AM 1.5G irradiation (100 mW cm−2), a maximum power conversion efficiency (η) of 4.09% is obtained for the WD11-based DSSC, higher than that of DTF-free dye L0 (η = 2.47%). These results have demonstrated that the incorporation of the DTF group into the organic dye will be an effective approach to develop high-performance metal-free organic dyes.

Study on the Preparation and Properties of Colored Iron Oxide Thin Films

Colored iron oxide thin films were prepared using Sol-gel technique. The raw materials were tetraethyl orthosilicate (TEOS), etoh ehanol (EtOH), iron nitrate, and de-ionized water. Various properties were measured and analysed, including the colour of thin films, surface topography, UV-Visible spectra, corrosion resistance and hydrophobicity. To understand how these properties influenced the structural and optical properties of Fe2O3 thin films, Scanning Electron Microscope (SEM), UV Spectrophotometer and other facilities were employed. Many parameters influence the performance of thin films, such as film layers, added H2O content, and the amount of polydimethylsiloxane (PDMS). When the volume ratio of TEOS, EtOH and H2O was 15: 13: 1, the quality of Fe(NO3)3·9H2O was 6g, and pH value was 3, reddish and uniform Fe2O3 thin films with excellent properties were produced. Obtained thin films possessed corrosion resistance in hydrochloric acid with pH=l and the absorption edge wavelength was ~350.2nm. Different H2O contents could result in different morphologies of Fe2O3 nanoparticles. When 1.5 ml PDMS was added into the Sol, thin films possessed hydrophobiliry without dropping. Coating with different layers, thin films appeared different morphologies. Meanwhile, with the increment of film layers, the absorbance increased gradually.