SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Energy conversion efficiency

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Nanoclay minerals play a promising role as additives in the liquid electrolyte to form a gel electrolyte for quasi-solid-state dye-sensitized solar cells because of their high chemical stability, unique swelling ability, ion exchange capacity and rheological properties. Here we report the improved performance of a quasi-solid-state gel electrolyte comprising a liquid electrolyte and synthetic nitrate-hydrotalcite nanoclay. Charge transport mechanism in the gel electrolyte, and nanoclay interactions with TiO2/electrolyte interface are discussed in detail. The electrochemical analysis reveals that the charge transport is solely based on physical diffusion. The calculated physical diffusion coefficient shows that the diffusion of redox ions is not much affected by the viscosity of nanoclay gel. The addition of nitrate-hydrotalcite clay in electrolyte has the effect of buffering the protonation process at TiO2/electrolyte interface, resulting in conduction band up-shift and a boost in Voc. Higher Voc with undiminished photocurrent is achieved with nitrate-hydrotalcite nanoclay gel electrolyte for organic as well as for inorganic dye (D35 and N719) systems. 10 % improvement in the efficiency for hydrotalcite clay gel electrolyte is obtained, compared to that of the liquid electrolyte. The power conversion efficiency can be achieved as high as 10.1% under 0.25 sun and 9.6% under full sun. This study demonstrates that nitrate-hydrotalcite nanoclay in the electrolyte not only solidifies the liquid electrolyte to prevent solvent leakage, but also facilitates the improvement in cell efficiency.  

Concepts: Energy conversion efficiency, Electrochemistry, Thin film solar cell, Physical chemistry, Dye-sensitized solar cell, Energy conversion, Titanium dioxide, Solar cell

28

We report a novel approach for synthesizing CdS and CdSe quantum dots subsectionally sensitized double-layer ZnO nanorods for solar cells, which are comprised of CdS QDs-sensitized bottom-layer ZnO NRs and CdSe QDs-sensitized top-layer ZnO NRs. X-ray diffraction study and scanning electron microscopy analysis indicate that the solar cells of subsectionally sensitized double-layer ZnO NRs, which are the hexagonal wurtzite crystal structure, have been successfully achieved. The novel structure enlarged the range of absorbed light and enhanced the absorption intensity of light. The I-V characteristics show that the double-layer structure improved both the current density (J(sc)) and fill factor (FF) by 50%, respectively, and power conversion efficiency (η) was increased to twice in comparison with the CdS QDs-sensitized structure.

Concepts: Energy conversion efficiency, Cadmium telluride, X-ray, Photoelectric effect, Cadmium, Light, Electron, Solar cell

28

The tungsten sulfide/multi-wall carbon nanotube (WS2/MWCNT) hybrid was prepared in the presence of glucose by in suit hydrothermal route. The hybrid materials was used as counter electrode in dye-sensitized solar cell (DSSC). The results of cyclic voltammetry measurement and electrochemical impedance spectroscopy indicated that the glucose aided prepared (G-A) WS2/MWCNT electrode had low charge-transfer resistance (Rct) and high electrocatalytic activity for triiodide reduction. The excellent electrochemical properties for (G-A) WS2/MWCNT electrode is due to the synergistic effects of WS2 and MWCNTs, as well as amorphous carbon introduced by glucose. The DSSC based on the G-A WS2/MWCNT counter electrode achieved a high power conversion efficiency of 7.36%, which is comparable with the performance of the DSSC using Pt counter electrode (7.54%).

Concepts: Titanium dioxide, Energy conversion efficiency, Thin film solar cell, Dye-sensitized solar cell, Energy conversion, Carbon, Solar cell, Electrochemistry

28

We demonstrate series-integrated multijunction organic photovoltaics fabricated monolithically by vapor-deposition in a transposed subcell order with the near-infrared-absorbing subcell in front of the green-absorbing subcell. This transposed subcell order is enabled by the highly complementary absorption spectra of a near-infrared-absorbing visibly-transparent subcell and a visible-absorbing subcell and motivated by the non-spatially-uniform optical intensity in nanoscale photovoltaics. The subcell order and thicknesses are optimized via transfer-matrix formalism and short-circuit current simulations. An efficient charge recombination zone consisting of layers of BCP/Ag/MoOx leads to negligible voltage and series-resistance losses. Under 1-sun illumination the multijunction solar cells exhibit a power conversion efficiency of 5.5 ± 0.2% with an FF of 0.685 ± 0.002 and a V(OC) of 1.65 ± 0.02 V, corresponding to the sum of the V(OC) of the component subcells. These devices exhibit a broad spectral response (in the wavelength range of 350 nm to 850 nm) but are limited by subcell external quantum efficiencies between 20% and 30% over the photoactive spectrum.

Concepts: Spectrum, Energy conversion efficiency, Absorption, Photovoltaic module, Photovoltaics, Energy conversion, Light, Solar cell

28

Open structure ZnO/CdSe core/shell nanoneedle arrays were prepared on a conducting glass (SnO2:F) substrate by solution deposition and electrochemical techniques. A uniform CdSe shell layer with a grain size of approximately several tens of nanometers was formed on the surface of ZnO nanoneedle cores after annealing at 400 [degree sign]C for 1.5 h. Fabricated solar cells based on these nanostructures exhibited a high short-circuit current density of about 10.5 mA/cm2 and an overall power conversion efficiency of 1.07 % with solar illumination of 100 mW/cm2. Incident photo-to-current conversion efficiencies higher than 75 % were also obtained.

Concepts: Glass, Direct current, Cadmium telluride, Light, Energy conversion, Electric current, Energy conversion efficiency, Solar cell

27

The recent stunning rise in power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) has triggered worldwide intense research. However, high PCE values have often been reached with poor stability at an illuminated area of typically less than 0.1 cm(2). We used heavily doped inorganic charge extraction layers in planar PSCs to achieve very rapid carrier extraction even with 10-20 nm thick layers avoiding pinholes and eliminating local structural defects over large areas. This robust inorganic nature allowed for the fabrication of PSCs with an aperture area >1 cm(2) showing a power conversion efficiency (PCE) >15% certified by an accredited photovoltaic calibration laboratory. Hysteresis in the current-voltage characteristics was eliminated; the PSCs were stable: >90% of the initial PCE remained after 1000 hours light soaking.

Concepts: Photovoltaic array, Robust statistics, Photovoltaic module, P-n junction, Photovoltaics, Energy conversion, Energy conversion efficiency, Solar cell

27

Large area pixelated polymer solar cell design with active encapsulants for down-conversion and redirecting light is demonstrated by K. S. Narayan and Anshuman J. Das on page 2193. The large-area, vacuum-free fabrication is carried out using meltable alloys as cathodes and an architecture which permits channelizing the light back into the device utilizing appropriate fluorescent dye molecules embedded in the encapsulant.

Concepts: Photoelectric effect, Quantum dot, Light, Energy conversion, Solar cells, Organic solar cell, Energy conversion efficiency, Solar cell

27

Replacement of the TiO2 layer in a traditional dye sensitized solar cell (DSC) by poly[3-(2-hydroxyethyl)-2,5-thienylene] grafted reduced graphene oxide (PHET-g-rGO) yields an overall power conversion efficiency of 3.06% with the N-719 dye, where the rGO part increases the charge mobility by reducing the backward recombination reaction in the DSC.

Concepts: Electrochemistry, Solar cells, IBM, Cadmium, Energy conversion, Titanium dioxide, Energy conversion efficiency, Solar cell

27

A novel conjugated side-chain polymer (PBDT-TID), based on benzo[1,2-b:4,5-b']dithiophene (BDT) and isoindigo (ID) moieties, was designed and synthesized. The new polymer exhibited excellent microphase separation in active layers. Bulk heterojunction polymer solar cells fabricated from PBDT-TID and PC61BM showed promising power conversion efficiencies of 5.25% and 6.51% using conventional and inverted device structures, respectively.

Concepts: United Kingdom, Substituent, Energy conversion, Organic solar cell, Energy conversion efficiency, P-n junction, Amino acid, Solar cell

27

Enhanced photovoltaic performance of a DSSC using graphene-TiO2 photoelectrodes prepared by our recent in situ simultaneous reduction-hydrolysis technique (Adv. Funct. Mater., 2012, DOI: 10.1002/adfm.201202349, in press) was achieved. The DSSCs based on the G-TiO2 nanocomposites improved their overall energy conversion efficiency to 7.1%. The results prove that the promoting effect of graphene is strongly dependent on its content; namely, the efficiency of DSSCs increases and then decreases with increasing graphene content in TiO2-graphene composites. Excessive graphene in the nanocomposite leads to a decrease of the light harvest of dye molecules and thus a negative effect on the power conversion efficiency of DSSCs.

Concepts: Thermodynamics, Energy transformation, Photovoltaics, Nanomaterials, Energy, Energy conversion efficiency, Energy conversion, Solar cell