Auttasit Tubtimtae

ZnO-Nanorod Dye-Sensitized Solar Cells: New Structure without a Transparent Conducting Oxide Layer

Conventional nanorod-based dye-sensitized solar cells (DSSCs) are fabricated by growing nanorods on top of a transparent conducting oxide (TCO, typically fluorine-doped tin oxide—FTO). The heterogeneous interface between the nanorod and TCO forms a source for carrier scattering. This work reports on a new DSSC architecture without a TCO layer. The TCO-less structure consists of ZnO nanorods grown on top of a ZnO film. The ZnO film replaced FTO as the TCO layer and the ZnO nanorods served as the photoanode. The ZnO nanorod/film structure was grown by two methods: (1) one-step chemical vapor deposition (CVD) (2) two-step chemical bath deposition (CBD). The thicknesses of the nanorods/film grown by CVD is more uniform than that by CBD. We demonstrate that the TCO-less DSSC structure can operate properly as solar cells. The new DSSCs yield the best short-current density of 3.96 mA/ c m 2 and a power conversion efficiency of 0.73% under 85 mW/ c m 2 of simulated solar illumination. The open-circuit voltage of 0.80 V is markedly higher than that from conventional ZnO DSSCs.

MnTe semiconductor-sensitized boron-doped TiO2 and ZnO photoelectrodes for solar cell applications.

We report a new tailoring MnTe semiconductor-sensitized solar cells (MnTe SSCs) using successive ionic layer adsorption and reaction (SILAR) technique. X-ray diffraction and SAED patterns reveal the orthorhombic MnTe and cubic MnTe2 phases were grown on boron-doped TiO2 and ZnO nanoparticles. The diameter of MnTe NPs ranged from 15 to 30nm on both B-doped metal oxide structures. The energy gaps of metal oxide become narrower after boron doping, which have an advantage for enhancing the light absorption from UV to visible region. Also, the energy gap of MnTe NPs on B-doped metal oxide was determined ~1.27-1.30eV. The best power conversion efficiency (η) of 0.033% and 0.030% yielded from B-doped TiO2/MnTe(7) and B-doped ZnO/MnTe(9), respectively. The reduction in power conversion efficiency by 103% and 91% was due to the absence of boron doping into TiO2 and ZnO nanostructures, respectively.

Effective performance for undoped and boron-doped double-layered nanoparticles-copper telluride and manganese telluride on tungsten oxide photoelectrodes for solar cell devices

This work demonstrates the synthesis of a novel double-layered Cu2-xTe/MnTe structure on a WO3 photoelectrode as a solar absorber for photovoltaic devices. Each material absorber is synthesized using a successive ionic layer adsorption and reaction (SILAR) method. The synthesized individual particle sizes are Cu2-xTe(17) ∼5-10nm and MnTe(3) ∼2nm, whereas, the aggregated particle sizes of undoped and boron-doped Cu2-xTe(17)/MnTe(11) are ∼50 and 150nm, respectively. The larger size after doping is due to the interconnecting of nanoparticles as a network-like structure. A new alignment of the energy band is constructed after boron/MnTe(11) is coated on boron/Cu2-xTe nanoparticles (NPs), leading to a narrower Eg equal to 0.58eV. Then, the valence band maximum (VBM) and conduction band minimum (CBM) with a trap state are also up-shifted to near the CBM of WO3, leading to the shift of a Fermi level for ease of electron injection. The best efficiency of 1.41% was yielded for the WO3/boron-doped [Cu2-xTe(17)/MnTe(11)] structure with a photocurrent density (Jsc)=16.43mA/cm(2), an open-circuit voltage (Voc)=0.305V and a fill factor (FF)=28.1%. This work demonstrates the feasibility of this double-layered structure with doping material as a solar absorber material.

Undoped and Manganese2+-doped polycrystalline Cd1−xInxTe sensitizer for liquid-junction solar cell devices

Ternary Cd1-xInxTe semiconductor nanoparticles have been demonstrated to be sensitizers for solar cell devices. The chemical bath deposition (CBD) process was used to synthesize Cd1-xInxTe nanoparticles, which were deposited onto a mesoporous TiO2 photoelectrode. Individual nanoparticles were estimated to have an average diameter range of ∼10nm. The atomic percentages of chemical elements for Mn(2+)-doped Cd1-xInxTe show that the structure could be Mn(2+)-doped CdInTe incorporated with CdIn2Te4 structure. The resulted X-ray diffraction and diffraction ring patterns of Mn(2+)-doped Cd1-xInxTe nanoparticles indicated the structure to be tetragonal. The optical band gaps were also decreased to 0.9eV after Mn(2+) doping, compared with Eg=1.47eV for undoped Cd1-xInxTe(7). The best efficiency of 0.51% under 100 mW/cm(2) (AM 1.5G) was obtained after Mn(2+) doping with a short-circuit current density (Jsc) of 1.71mA/cm(2), an open-circuit voltage (Voc) of 0.739V and a fill factor (FF) of 40.2%. This work demonstrated the feasibility of using Cd1-xInxTe with Mn(2+) doping as a broadband solar absorber for TiO2 photoelectrodes.

Photovoltaic performances of Cu2−xTe sensitizer based on undoped and indium3+-doped TiO2 photoelectrodes and assembled counter electrodes

Novel binary Cu2-xTe nanoparticles based on undoped and indium-doped TiO2 photoelectrodes were synthesized using a successive ionic layer adsorption and reaction (SILAR) technique as a sensitizer for liquid-junction solar cells. A larger diameter of TiO2 promoted a narrower energy band gap after indium doping, attributing to yield a broader absorption range of nanoparticle sensitizer due to the increasing amount of Cu2-xTe NPs on TiO2 surface. The atomic percentages showed the stoichiometric formation of Cu2Te incorporated in a Cu2-xTe structure. The best photovoltaic performance with the lower SILAR cycle, i.e., n=13 was performed after indium doping in both of carbon and Cu2S CEs and revealed that the efficiency of 0.73% under the radiant 100mW/cm(2) (AM 1.5G). The electrochemical impedance spectroscopy (EIS) was used to investigate the electrical properties via effect of material doping and counter electrodes with a lower charge-transfer resistance (Rct) and it was also found that the electron lifetime was improved after the sample doped with indium and assembled with carbon CE.

Optical and Photovoltaic Properties of CdS/Ag2S Quantum Dots Co-Sensitized-Solar Cells

Subscript textWe present a co-sensitization of CdS/Ag2S quantum-dot as sensitizers for solar cells. The optical properties of single and double-layered quantum-dot conditions were monitored using UV-Vis spectrophotometer. The results show that the different characteristics of absorption spectra depended on the types of QDs, indicating to the different energy gap of each QDs deposited on TiO2 surface and the tunable absorption ranges of the sample of double-layered quantum-dot-sensitized TiO2 electrodes are broader and the absorption intensity are higher than the single-layered quantum-dot, attributed to the co-absorption of two QDs to the light and both CdS and Ag2S are activated in visible to near-infrared region (450-1100 nm). The photovoltaic data shows that the highest efficiency of 1.41% with a photocurrent density, Jsc of 20.6 mA/cm2, an open-circuit voltage, Voc of 0.32 V and a fill factor, FF of 21.3% were yielded by the sample of CdS(3)/Ag2S(4) as an optimum condition of dipping cycles for CdS and Ag2S under irradiance of 100 mW/cm2 (AM 1.5G).

Deposition Time Dependent Properties of Copper Tin Telluride (Cu2SnTe3) Nanoparticles for Solar Absorber Applications

We report the growth of copper tin telluride nanoparticles as an absorber layer using a chemical bath deposition (CBD) process for solar selective applications. The XRD results showed the phase of Cu2SnTe3 with a cubical structure. The larger-sized nanoparticles resulted with increased absorption properties and the optical band gap ranging from 1.93, 1.90, 1.58 and 1.56 eV for deposition times of 20-120 min, respectively. Then, the electrical properties of Cu2SnTe3 nanoparticles were also provided a higher current (~6-8 mA) with bias potential of zero.

Boron-doped MnTe semiconductor-sensitized ZnO solar cells

We studied the photovoltaic performance of boron-doped MnTe semiconductor-sensitized solar cells (B-doped MnTe SSCs). The B-doped MnTe semiconductor was grown on ZnO using two stages of the successive ionic layer adsorption and reaction (SILAR) technique. The two phases of B-doped semiconductor nanoparticles (NPs), i.e. MnTe and MnTe2 were observed with a diameter range of approximately 15–30 nm. The result of the energy conversion efficiency of the sample with boron doping was superior compared to that of an undoped sample, due to the substantial change in the short-circuit current density and the open-circuit voltage. In addition, plots of (αhv)2 vs hv with band gaps of 1.30 and 1.27 eV were determined for the undoped and B-doped MnTe NPs, respectively. It can be noted that the boron doping effects with the change in the band gap and lead to an improvement in the crystalline quality and also intimate contact between the larger sizes of MnTe NPs. Hence, a noticeably improved photovoltaic performance resulted. However, this kind of semiconductor sensitizer can be further extended by experiments on yielding a higher power conversion efficiency and greater stability of the device.

Ethanol Sensor Based on Au-doped ZnO Nanostructures

Ethanol sensing characteristics of ethanol sensor based on Au-doped ZnO nanostructures were studied. Au-doped ZnO nanostructures with 5% gold by weight were prepared by thermal oxidation technique. The sintering time was varied for 6 hours and 24 hours. The wire-like or belt-like nanostructures with the sharp ends outward from microparticles were observed. The diameter and length of ZnO nanostructures are in the range of 250-750 nm and 1.7-7.0 mum, respectively, with the average diameter of 500 nm. EDS spectrum shows Au signal confirming incorporation of Au into ZnO nanostructures. For 24 hours sintering time, the diameter and length of ZnO nanostructures are 170-500 nm and 2.0-7.0 jim, respectively, with the average diameter of 330 nm. The average diameter for 24 hours sintering time is smaller than that of 6 hours sintering time. The response and recovery characteristics of Au-doped ZnO nanostructures upon exposure to ethanol concentration of 1000 ppm at different operating temperatures suggest that the sensitivity depend on operating temperatures. It is found that the highest sensitivity is 88 at 280 degC for 6 hours sintering time and about 170 at 300-320 degC for 24 hours sintering time. The longer sintering times the higher the sensitivity. The enhancement of sensitivity for longer sintering time may be explained in terms of the smaller size of nanostructures due to the increase of effective surface for absorption of ethanol on the surface.

Manganese2+-Doped Copper Tin Telluride Absorber Layer-Sensitized Solar Cells

Manganese2+-doped copper tin telluride nanoparticles (Mn2+:Cu2SnTe3 NPs), as an absorber layer, were grown using a chemical bath deposition (CBD) technique and demonstrated for solar cell applications. The cubical structure was formed on the WO3 surface with the band gap (Eg) of Cu2SnTe3 NPs decreased from 1.80 to 1.67 eV after Mn2+ doping. The photovoltaic property at 1 sun shows the efficiency (η) of 0.276%. The η was increased with reducing sunlight intensity due to the lower carrier recombination process at an electrode and electrolyte interface, which leads to the increasing η. The highest η of 1.120% was yielded at 0.1 sun with a Jsc = 2.81 mA/cm2, a Voc = 0.148 V, a FF = 26.8%. It can be noted that this kind of material and a synthesis procedure can be feasibly further improved for a higher efficiency and more stability on an absorber layer.