At Air Mass Research Articles

Strategies for Tuning Optoelectronic Properties of TiO2 Nanomaterials for Solar Photovoltaic Studies

Third generation solar cells are mainly focusing on the use of nanomaterials as host components for solar-to-electrical conversions. Among the various nanomaterials, TiO2 is one of the most promising candidates used in solar devices due to their remarkable structural and opto-electrical properties. However, bare TiO2 nanomaterials have the various constraints in efficient solar energy conversions. In the present research endeavors, TiO2 nanomaterials have been modified with the different strategies such as dyad anchoring, dye-quantum dot sensitization, composites of carbon nanostructures with sensitizers, metal ion doping with sensitizers so as to tune its optoelectronic properties for efficient solar energy harvesting. In addition, the interconnectivity between the various components and their optoelectronic properties of modified TiO2 for solar energy conversions have been studied in detail. In the dyad system, a supramolecular ruthenium(II)phthalocyanine··peryleneimide (RuPc···PI) has been anchored on the surfaces of TiO2 and thereafter these TiO2-dyad sensitized solar cells have assembled in a bottom-up fashion. Upon photo-irradiation at air-mass (AM) 1.5, the dyad-based solar devices convert solar light to electricity of 2.1%; which is higher than that of individual dyes. In next strategies, the synthesized CdS quantum dots (QDs) have connected electrostatically to the surfaces of TiO2 nanoparticles (NPs) and thereafter, this binary hybrid heterojunction is further self-assembled physically with N719 dye to form ternary TiO2 NPs-CdS QDs-N719 photoelectrodes. These co-sensitization devices reported the solar energy conversion efficiency (η) up to 2.35 %. In addition, anatase TiO2 NPs is anchored on the surface of functionalized carbon nanostructures (MWCNTs or RGO); which is further sensitized with Ru(II) dyes for solar devices having efficiency reached to 6.21%. In another modification, Cr(III) as well as Mo(VI) ions are inserted into TiO2 host lattice and then their composites with CNs are further sensitized for boosting the solar energy conversions and reached up to 7.69 % of efficiency. Figure 1

Study of ultra-thin CdTe/CdS heterostructure solar cell purveying open-circuit voltage ∼1.2 V

This study focuses on aiming higher stabilized sunlight to electricity conversion efficiency for Cadmium Telluride (CdTe) absorber based solar cell. Common CdTe solar cell with Au back or Zinc Telluride (ZnTe) back surface field (BSF) with Cu back metal has voltages < 1V. The reason behind this low voltage has been investigated in details. In this report, simulation yielding of (M = Cu, Ni, Au, Ir, Pd, and Pt) thin-film solar cell (TFSC) has been presented. The solar cell has been modelled and analyzed using Analysis of Microelectronic and Photonic Structures – 1 Dimensional (AMPS-1D) device simulator for various back metals with work function, Φm ≥ 5 eV. The thickness was varied from 100–1800 nm, and from 15–100 nm for the active p-CdTe absorber, and n-Cadmium Sulphide (CdS) window layers, respectively, to optimize the device depth. Meanwhile, the donor and acceptor concentration was varied to outline their effects on photovoltaic (PV) parameters. The utmost efficiency (η) of ∼30% along with open circuit voltage of 1.194 V, short circuit current density of 28.6 mA cm−2, and fill factor (FF) of 89.3% has been achieved ideally with Platinum (Pt) back contact at (111) plane under standard test conditions (STC) of and 1 Sun illumination (1000 W m−2) at air mass (AM) 1.5. Lastly, the cell operating temperature was varied from to to verify the thermal stability of the proposed structure. Present work provides a guideline to select back metal in CdTe solar cell. Our proposed solar cell offers the prospect of being a highly efficient cost effective second generation (2G) TFSC.

Dye-sensitized solar cells based on composite TiO2 nanoparticle–nanorod single and bi-layer photoelectrodes

TiO2 nanoparticle (NP), composite TiO2 nanoparticle–nanorod (NP–NR) and bi-layer TiO2 nanoparticle/nanorod (NP/NR) with the optimized diameter of NRs had been prepared as anode layer in dye-sensitized solar cells (DSSCs). Morphology and thickness of anode layers were provided by field emission scanning electron microscope (FE-SEM) and scanning electron microscopy (SEM) devices. Current density–voltage diagrams were prepared by potentiostat and solar simulator devices at air mass (AM) 1.5. It is determined that DSSCs based on composite NP–NR photoelectrode had the best conversion efficiency of 5.07%. Also, the results of the electrochemical modelling of these DSSCs indicated that solar cells based on NP–NR electrode had the highest electron transport time (τ d) of 312.87 ms, electrons’ recombination lifetime (τ n) of 130.4 ms and the lowest transfer resistance (R ct) as well as transport resistance (R t) of 22.46 and 9.4 Ω, respectively.

Efficiency Estimations for Multijunction and Intermediate Band Solar Cells Using Actual Measured Solar Spectra in Japan

An intermediate band solar cell (IBSC) whose equivalent circuit is similar to a multijunction (MJ) solar cell but with an additional parallel diode connection is shown to be more robust to spectral variation than a series-connected MJ solar cell. We have calculated the limiting efficiencies of IBSC and MJ solar cells using the measured solar spectra in Japan. Even though the maximum efficiency of an IBSC is lower than a triple junction (3J) solar cell at airmass (AM)1.5, the IBSC would generate more annual electricity by 1% than 3J cell at 1 sun, if they had been optimized at AM1.5.

Fabrication of P-Type ZnO:N Film by Radio-Frequency Magnetron Sputtering for Extremely Thin Absorber Solar Cell Applications

We successfully fabricate p-type ZnO:N films by using rf magnetron sputtering and in situ annealing in O2 atmosphere. These p-type ZnO:N films can be used as p-type window materials for extremely thin absorber (ETA) solar cells composed of quartz glass/p-ZnO:N/i-ZnO/CdSe/i-ZnO/n-ZnO:Al. The short-circuit photocurrent density, open circuit voltage, fill factor and conversion efficiency of the ETA solar cells can be determined to be 8.549 mA/cm2, 0.702V, 0.437 and 2.623%, respectively, through measurements of photovoltaic properties under illumination with a 100mW/cm2 at air-mass (AM) 1.5.

A molecularly engineered fluorene-substituted Ru-complex for efficient mesoscopic dye-sensitized solar cells

A new high molar extinction coefficient ruthenium(II) bipyridyl complex ‘cis-Ru(L1)(2,2′-bipyridine-4,4′-dicarboxylic acid) (NCS)2, BDF’, where L1=4,4-bis(9,9-dibutyl-9H-fluorene-2-yl)-[2,2] bipyridine, has been synthesized and characterized by Fourier transform infrared (FTIR), hydrogen nuclear magnetic resonance (1 H-NMR) and electrospray ionization mass (ESI–MASS) spectroscopes. The dye, upon anchoring onto mesoporous nano-crystalline TiO 2 solar cells, exhibited a broader photocurrent action spectrum, with a solar-to-electric energy conversion efficiency (η) of 6.58% (J SC =14.66 mA cm −2, V OC =640 mV, fill factor=0.71) under sunlight at air mass (AM) 1.5, larger than the reference Z907 sensitized solar cell fabricated under similar conditions, which exhibited an η-value of 4.65% (J SC =11.52 mA cm −2, V OC =566 mV, fill factor=0.72). Absorption measurements and time-dependent density functional theory (TDDFT) calculations show that the increased conjugation length by introducing 9,9-dibutyl-9H-fluorene moiety relatively enhances the spectral response of the ancillary ligand and the corresponding BDF complex. The calculated dipole moments for BDF and Z907 are 17.71 and 16.34 Debye, respectively. The first three highest occupied molecular orbitals (HOMOs) of BDF have a t 2g character, as observed in Z907, while HOMO-4 and HOMO-5 have considerable sizable mixing from Ru-NCS with π-orbitals of L1.

Charge Separation and Efficient Light Energy Conversion in Sensitized Mesoscopic Solar Cells Based on Binary Ionic Liquids

A 7.4% power conversion efficiency at air mass (AM) 1.5 full sunlight was reached with a mesoscopic solar cell employing a new binary ionic liquid electrolyte composed of 1-propyl-3-methylimidazolium iodide and 1-ethyl-3-methylimidazolium tricyanomethanide in conjunction with the amphiphilic ruthenium complex NaRu(4-carboxylic acid-4'-carboxylate)(4,4'-dinonyl-2,2'-bipyridine)(NCS)(2), coded as Z-907Na. Ultramicroelectrode voltammetric, nanosecond laser transient absorbance, and photovoltaic measurements show that a high iodide concentration is required for dye regeneration to compete efficiently with charge recombination. A surprisingly fast reductive quenching process is turned on in pure iodide melts. This channel is unproductive, explaining the lower photocurrents observed under these conditions.

Optical properties of higher and lower refractive index composites in solar selective coatings

The focus of attention in this study was the choice of material for optically solar selective coatings on the basis of their optical constants. A computer programme which calculates the optical constants, solar absorptance at air mass (AM)-2, α, and thermal emittance at 300 K, ε, of the 200-nm-thick selective coating on the assumption of both the Maxwell Garnett and Bruggeman theories for the metallic volume fraction below and above 0.3 respectively, was used to design the structure of the composite films. Two systems of composite thin films of metal and dielectric were investigated experimentally, fabricated by RF and DC sputter coater and were verified with computer simulations. One system consist of lower refractive index composites such as Ni : SiO 2 and the other of higher refractive index composites such as V : Al 2O 3 in the spectral range of 0.3–20 μm. These films were fabricated on infrared reflective substrates such as nickel plated copper or aluminium. Results of the copper substrates are being presented here. For comparison and verification, tungsten, cobalt and chromium based composites, having different refractive indices, were also investigated which validated the concept of the choice of material in selective coatings. It was observed that high refractive index composites have lower reflective properties by choosing suitable metallic volume fraction in dielectric and antireflection coating. The higher value of the imaginary part of refractive index, k, is responsible for higher absorption by a factor α λ =4 πk/ λ. Solar absorptance of 0.98 and 0.96 was achieved by simulation and experimental findings with less than 0.05 thermal emittance for 200 nm thick composites of V : Al 2O 3. It results that higher values of both n and k of the material are more suitable in solar selective coatings.

Over 27% efficiency GaAs/InGaAs mechanically stacked solar cell

We have applied an InGaAs solar cell (band gap = 0.75 eV) to the bottom cell of the super-high-efficiency tandem solar cell aiming an over 35% conversion efficiency. The InGaAs cell which is lattice-matched to the InP substrate showed the efficiency of 5.5% under the GaAs substrate with low carrier concentration. Combining with the GaAs cell by means of a mechanically stacking technique, we obtained an efficiency of 28.8% at air mass (AM) 1.5, 1-sun. This result suggests the possibility of the cells with the efficiency of over 35% with combining a GalnP/GaAs monolithic tandem cell and the InGaAs cell (or InGaAsP cell).