Dye-Sensitized Solar Cells with a High Absorptivity Ruthenium Sensitizer Featuring a 2-(Hexylthio)thiophene Conjugated Bipyridine

We conjugated 2-(hexylthio)thiophene with bipyridine to construct a new heteroleptic polypyridyl ruthenium sensitizer exhibiting a charge-transfer band at 550 nm with a molar extinction coefficient of 18.7 x 10(3) M-1 cm(-1). In contrast to its analogues Z907 and C101, a mesoporous titania film stained with this new sensitizer featured a short light absorption length, allowing for the use of a thin photoactive layer for efficient light-harvesting and conversion of solar energy to electricity. With a preliminary testing, we have reached 11.4% overall power conversion efficiency measured at the air mass 1.5 global conditions. Transient photoelectrical decays and electrical impedance spectra were analyzed to picture the intrinsic physics of temperature-dependent photovoltage and photocurrent.

Dye-Sensitized Solar Cells Based on Organic Sensitizers with Different Conjugated Linkers: Furan, Bifuran, Thiophene, Bithiophene, Selenophene, and Biselenophene

Six organic dyes with different conjugated linkers such as furan, bifuran, thiophene, bithiophene, selenophene, and biselenophene have been prepared in combination with the dihexyloxy-substituted triphenylamine donor and the cyanoacrylic acid acceptor. In conjunction with an acetonitrile-based electrolyte and a solvent-free ionic liquid electrolyte, these dyes exhibit 6.88-7.77% and 6.39-7.00% efficiencies, respectively. We have demonstrated that furan and selenophene can be employed as building blocks of sensitizers in stable solar cells for the first time. We have also studied the influence of heteroatoms on photocurrents and photovoltages with the aid of quantum calculations and transient photoelectrical decay measurements. Temperature-dependent electrical impedance experiments have shown that a relatively low external quantum efficiency of the dye with biselenophene linker is not related to the charge collection yield in the case of an acetonitrile electrolyte.

An Extremely High Molar Extinction Coefficient Ruthenium Sensitizer in Dye-Sensitized Solar Cells: The Effects of pi-Conjugation Extension

We report a heteroleptic ruthenium complex (007) featuring the electron-rich 5-octyl-2,2'-bis(3,4-ethylenedioxythiophene) moiety conjugated with 2,2-bipyridine and exhibiting 10.7% power conversion efficiency measured at the AM1.5G conditions, thanks to the enhanced light-harvesting that is closely related to photocurrent. This C107 sensitizer has an extremely high molar extinction coefficient,of 27.4 x 10(3) M-1 cm(-1) at 559 nm in comparison to its analogue C103 (20.5 x 10(3) M-1 cm(-1) at 550 nm) or Z907 (12.2 x 10(3) M(-1)cm(-1) at 521 nm) with the corresponding 5-hexyl-3,4-ethylenedioxythiopliene- or nonyl-substituted bipyridyl unit. The augmentation of molar extinction coefficients and the bathochromic shift of low-energy absorption peaks along with the pi-conjugation extension are detailed by TD-DFT calculations. The absorptivity of mesoporous titania films grafted with Z907, C103, or C107 sublinearly increases with the molar extinction coefficient of sensitizers, which is consistent with the finding derived from the surface coverage measurements that the packing density of those sensitizers decreases with the geometric enlargement of ancillary ligands.

Solid-state dye-sensitized solar cells using TiO2 nanotube arrays on FTO glass

Highly ordered, vertically oriented TiO2 nanotube arrays were prepared by potentiostatic anodization of titanium on FTO-coated glass substrate and for the first time successfully applied in the fabrication of solid-state dye sensitized solar cells (SSDSCs), giving a power conversion efficiency of 1.67% measured under an irradiation of air mass 1.5 global (AM 1.5 G) full sunlight. Furthermore, 3.8% efficiency was reached with a 2.8 mu m thin TiO2 nanotube array film based on a metal free organic dye using ionic liquid electrolyte.

The effects of shell characteristics on the current-voltage behaviors of dye-sensitized solar cells based on ZnO/TiO2 core/shell arrays

The ZnO/TiO2 core/shell structure was formed through deposition of a TiO2 coating layer on the hydrothermally fabricated ZnO nanorod arrays through radio frequency magnetron sputtering. The effects of the TiO2 shell's characteristics on the current-voltage behaviors of the core/shell-based dye-sensitized solar cells (CS-DSSC) were investigated. As the rates of injection, transfer, and recombination of electrons of such CS-DSSC were affected significantly by the crystallization, morphology, and continuity of the TiO2 shells, the photovoltaic efficiency was accordingly varied remarkably. In addition, the efficiency was further improved by enhancing the surface area in the core/shell electrode.

Toward high-performance polymer solar cells: The importance of morphology control

Polymer solar cells have the potential to become a major electrical power generating tool in the 21st century. R&D endeavors are focusing on continuous roll-to-roll printing of polymeric or organic compounds from solution-like newspapers-to produce flexible and lightweight devices at low cost. It is recognized, though, that besides the functional properties of the compounds the organization of structures on the nanometer level-forced and controlled mainly by the processing conditions applied-determines the performance of state-of-the-art polymer solar cells. In such devices the photoactive layer is composed of at least two functional materials that form nanoscale interpenetrating phases with specific functionalities, a so-called bulk heterojunction. In this perspective article, our current knowledge on the main factors determining the morphology formation and evolution is introduced, and gaps of our understanding on nanoscale structure-property relations in the field of high-performance polymer solar cells are addressed. Finally, promising routes toward formation of tailored morphologies are presented.

The fabrication of dipped CdS and sputtered ITO thin films for photovoltaic solar cells

Stable bilayer thin films of indium tin oxide (ITO) on CdS and CdS on ITO were formed for the window material of solar cells by chemical bath and sputtering methods. Scanning electron microscopy and X-ray diffraction studies have shown that both the ITO and CdS films are continuous, homogeneous, with high compactness. Measurement of the CdS film thickness across the 2 x 4 cm(2) reveals the good uniformity of these films. Four-point probe measurements show that the resistivity of a CdS film on an ITO surface is much better than that of the single CdS film The thermal stability of an ITO/CdS bilayer, interfacial reaction and optical transmittance were investigated at different annealing temperatures and environments (air, vacuum and N-2 + H-2). The results showed that the ITO/CdS bilayer film is a good window material for the CuInSe2 and CdTe cells. It is a simple method using a small amount of the cadmium compound.

Analysis of lateral current spreading in solar cell devices by spatially-resolved electroluminescence

Spatially-resolved electroluminescence (EL) images from solar cells contain information of local current distribution. By theoretical analysis of the EL intensity distribution, the current density distribution under a certain current bias and the sheet resistance can be obtained quantitatively. Two-dimensional numerical simulation of the current density distribution is employed to a GaInP cell, which agrees very well with the experimental results. A reciprocity theorem for current spreading is found and used to interpret the EL images from the viewpoint of current extraction. The optimization of front electrodes is discussed based on the results. (C) 2010 American Institute of Physics. [doi:10.1063/1.3431390]

Simulation of In0.65Ga0.35N single-junction solar cell

The performances of In0.65Ga0.35N single-junction solar cells with different structures, including various doping densities and thicknesses of each layer, have been simulated. It is found that the optimum efficiency of a In0.65Ga0.35N solar cell is 20.284% with 5 x 10(17) cm(-3) carrier concentration of the front and basic regions, a 130 nm thick p-layer and a 270 nm thick n-layer.

mc-Si : H/c-Si solar cell prepared by PECVD

Hetero-junction solar cells with an me-Si: H window layer were achieved. The open voltage is increased while short current is decreased with increasing the mc-Si:H layer's thickness of emitter layer. The highest of V-oc of 597 mV has obtained. When fixed the thickness of 30 nm, changing the N type from amorphous silicon layer to micro-crystalline layer, the efficiency of the hetero-junction solar cells is increased. Although the hydrogen etching before deposition enables the c-Si substrates to become rough by AFM images, it enhances the formation of epitaxial-like micro-crystalline silicon and better parameters of solar cell can be obtained by implying this process. The best result of efficiency is 13.86% with the V-oc of 549.8 mV, J(sc) of 32.19 mA center dot cm(-2) and the cell's area of 1 cm(2).

A COMPARATIVELY LOW-QUALITY SILICON MATERIAL IMPROVED FOR SOLAR-CELL FABRICATION

A comparatively low-quality silicon wafer (with a purity of almost-equal-to 99.9%) was adopted to form a silicon-on-defect-layer (SODL) structure featuring improved crystalline silicon near the defect layer (DL) by means of proton implantation and subsequent annealing. Thus, the SODL technique provides an opportunity to enable low-quality silicon wafers to be used for fabrication of low-cost solar cells.