Oxide Solar Cells Research Articles

Solution-processed all-oxide nanostructures for heterojunction solar cells

A low-cost, non-toxic, environmentally friendly, and solution-processed new oxide-based semiconducting material (Sn1−xCoxO2) was developed as an absorption material for all oxide solar cell fabrication in this work. The newly developed n-type cobalt-doped tin oxide (n-Sn1−xCoxO2) nanoparticles and p-type copper oxide (p-Cu2O) nanostructures were successfully synthesized via a low-temperature solution process. Combined with the use of non-vacuum spray and hot-press processes, the n-Sn1−xCoxO2/p-Cu2O heterojunction solar cells exhibit low-cost and large-scale fabrication advantages. The highest power conversion efficiency (PCE) of 1.2% can be obtained from the solar cells with n-Sn0.86Co0.14O2/p-Cu2O, under AM 1.5 illumination, a noteworthy improvement in solution-processed all-oxide-based nanostructures heterojunction solar cells.

Photoelectrochemical Investigation of Ultrathin Film Iron Oxide Solar Cells Prepared by Atomic Layer Deposition

Atomic layer deposition was used to grow conformal thin films of hematite with controlled thickness on transparent conductive oxide substrates. The hematite films were incorporated as photoelectrodes in regenerative photoelectrochemical cells employing an aqueous [Fe(CN)(6)](3-/4-) electrolyte. Steady state current density versus applied potential measurements under monochromatic and simulated solar illumination were used to probe the photoelectrochemical properties of the hematite electrodes as a function of film thickness. Combining the photoelectrochemical results with careful optical measurements allowed us to determine an optimal thickness for a hematite electrode of ∼20 nm. Mott-Schottky analysis of differential capacitance measurements indicated a depletion region of ∼17 nm. Thus, only charge carriers generated in the depletion region were found to contribute to the photocurrent.

Performance Improvement of Zinc Oxide Photoanode-Based Dye-Sensitized Solar Cells by Multi-Walled Carbon Nanotube

Unique electrical and surface-to-volume properties of carbon nanotubes have made these conductive molecules highly attractive in many applications. In this work, the influence of multi-walled carbon nanotubes into a zinc oxide active layer of dye-sensitized zinc oxide solar cell has been investigated. With this method, a significant improvement in the performance of the solar cell has been achieved. Compared to the typical zinc oxide photoelectrochemical cells, the photocurrent-voltage characteristics of the fabricated cell containing 0.05 percent by weight of carbon nanotubes in the metal oxide film displayed a higher short-circuit photocurrent, consequently caused an increase of the solar-to-electricity conversion efficiency by a factor of approximately 1.4. Further increase of the conductive carbon material resulted in a decrease of the energy conversion of the photovoltaic cell. The enhancement of the energy conversion at this optimum carbon nanotube loading may be attributed to the dye-adsorption ability and the electrochemical activity of the composite photoanodes. The fabricated photovoltaic cells with the highest efficiency exhibited the maximum dye adsorption intensity and the minimum charge transfer resistance, as measured by ultraviolet-visible spectroscopy and electrochemical impedance spectroscopy, respectively.

Simple Approach to Hybrid Polymer/Porous Metal Oxide Solar Cells from Solution-Processed ZnO Nanocrystals

This work is devoted to the development of hybrid bulk heterojunction solar cells based on porous zinc oxide (ZnO) electrodes and poly(3-hexylthiophene) (P3HT), using simple synthesis procedures and deposition techniques. Starting from ZnO nanocrystals with well-controlled properties, porous ZnO electrodes of suitable porosity are deposited by spin-coating, varying the main experimental parameters such as composition of the initial ZnO formulation and choice of the organic ligand. Significant charge transfer yields are observed in the corresponding solar cells, and the influence of processing conditions on device performance is investigated using conventional techniques as well as transient photovoltage/photocurrent decay measurements. The temperature used to sinter the ZnO electrode is found to be specifically crucial to ensure efficient charge transport in the device while avoiding a loss in interfacial area through nanocrystal coalescence. Using 8 × 13 nm ZnO nanorods, the best device exhibits a power ...

Hydrogenated Amorphous Silicon Oxide Solar Cells Fabricated near the Phase Transition between Amorphous and Microcrystalline Structures

We investigated the properties of hydrogenated amorphous silicon oxide (a-Si1-xOx:H) deposited near the phase transition between amorphous and microcrystalline structures. a-Si1-xOx:H films were prepared by plasma-enhanced chemical vapor deposition using a gas mixture of silane, hydrogen, and carbon dioxide. The film structure was changed from amorphous to microcrystalline phase by increasing hydrogen dilution. Optical and electrical characterizations revealed that wide-gap a-Si1-xOx:H films were deposited under phase transition conditions. We also fabricated a-Si1-xOx:H single-junction p–i–n solar cells by varying the hydrogen dilution for the i-layer. The solar cells showed a maximum open circuit voltage of 1.04 V (Jsc=7.92 mA/cm2, FF=0.64, Eff=5.2%) when the i-layer was deposited under phase transition conditions.

Improved Efficiency in Poly(3-hexylthiophene)/Zinc Oxide Solar Cells via Lithium Incorporation

The efficiency of poly(3-hexylthiophene)/zinc oxide planar heterojunction solar cells is on average raised by a factor of 2.9 by incorporating lithium during the sol−gel processing of the metal oxide layer. Studies performed on over 300 diodes show systematic increases in both open-circuit voltage (Voc) and short-circuit current (Jsc) up to an optimum Li concentration between 15 and 20 atom %. Compared to pure ZnO devices, the incorporation of lithium improves the Voc and Jsc by an average of 42 and 90%, respectively. For the best device, the efficiency increases by a factor of 7.5, yielding a power conversion efficiency of 0.44%, which is approaching the efficiency of the state-of-the-art nanostructured hybrid solar cells. Enhancements in Voc are attributed to a larger donor−acceptor energy band edge offset due to a rigid shift of Zn1−xLixO energy levels toward to the vacuum level with Li incorporation. Jsc improvements arise from a higher surface roughness with lithium incorporation and from better P3HT...

Hybrid polymer–metal oxide solar cells by in situ chemical polymerization

We present a new approach for improving the infiltration of a conjugated polymer into the pores of a nanostructured metal oxide electrode, whereby the polymer is prepared directly inside the porous oxide film by in situ chemical polymerization. We apply this method to the polymerisation of poly[2-methoxy-5-(2 ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) inside a nanostructured porous TiO2 layer by adapting the synthetic route based on the Gilch reaction. Transient and steady state optical studies show that the light absorption and emission properties of the polymer so produced are similar to those of the polymer synthesised ex situ, while the photoinduced charge separation yield is improved by in situpolymerisation. The photocurrent generated by hybrid polymer/metal oxide solar cells prepared by this methodology is enhanced by a factor of two to three relative to devices prepared with pre-synthesised polymer. The improved photocurrent and charge separation yield for the polymer produced in situ are attributed to improved infiltration of the polymer into the metal oxide film.

128 亜酸化銅太陽電池の性能に及ぼす銅素材中の亜酸化銅濃度の影響(材料力学II)

128 亜酸化銅太陽電池の性能に及ぼす銅素材中の亜酸化銅濃度の影響(材料力学II)

Novel thiophene-conjugated indolinedyes for zinc oxide solar cells

The application of a series of thiophene-conjugated indoline dyes for zinc oxide solar cells, prepared by the one-step cathode deposition template method, was examined. The introduction of thiophene ring(s) into D131-type indoline dye improved the cell performance due to their appropriate energy levels and bathochromic shift in the UV-vis absorption band on zinc oxide. It is important for the oxidation potential (Eox) of dyes to have a more positive value than ca. 0.25 V vs. Fc/Fc+ in acetonitrile in order to show a high (>70%) incident photon-to-current efficiency.

Effect of annealing on the resistivity of copper (I) oxide solar cells

The effect of annealing on the resistively of copper (I) oxides (Cu2O) samples has been investigated in detail. The resistivily of the sample is a function of the power output of such Cu2O solar cell. Results revealed that the annealing of Cu2O samples improves the output performance compared to that of unannealed samples by about 36%. The results on the resistivity of the samples oxidized at different temperatures for different times but annealed for some duration at an identical temperature after proper quenching in deionizer water shows a lower and higher resistivities for annealed and unannealed samples respectively. Key words: Annealed, unannealed, resistivity, quenching, Cu2O Solar Cell.

Design and Synthesis of Near-infrared-active Heptamethine–Cyanine Dyes to Suppress Aggregation in a Dye-sensitized Porous Zinc Oxide Solar Cell

Abstract New heptamethine–cyanine dyes were synthesized and used for dye-sensitization of porous zinc oxide cells in the near-infrared region (800 nm). The introduction of alkyl groups into the cyclohexene and indolenium moieties remarkably prevented H-aggregation of the dyes. Consequently, the photovoltaic performance of the dye-sensitized zinc oxide cells with DCA was improved; a solar-to-electricity conversion efficiency (η) of 0.67%, a short-circuit current density of 2.22 mA cm−2, an open-circuit photovoltage of 0.46 V, and a fill factor of 0.66 under standard AM 1.5 irradiation (100 mW cm−2).

High efficiency of CdSe quantum-dot-sensitized TiO2 inverse opal solar cells

The authors have demonstrated an approach to sensitized-type solar cells, based on TiO2 inverse opal and the use of CdSe quantum dots (QDs) as sensitizers. CdSe QDs were grown in situ on TiO2 inverse opal electrodes, utilizing a chemical bath deposition method. All of the photovoltaic performances, including short circuit photocurrent density, open circuit voltage, fill factor, and efficiency, were significantly improved by surface modification with ZnS and fluoride ions. A power conversion efficiency of about 2.7% has been attained, under solar illumination of 100mW∕cm2. This value is relatively high for metal oxide solar cells, sensitized with semiconductor QDs.

Flexible zinc oxide solar cells sensitized by styryl dyes

Application of a series of styryl dyes for flexible zinc oxide solar cells prepared by the one-step cathode deposition template method was examined. 3-(2-Carboxyethyl)-2-[4-(dimethylamino)styryl]benzothiazolium iodide ( 27) showed the best performance as the sensitizer. The incident photon-to-current efficiency (IPCE) at around 490 nm, maximum short-circuit photocurrent density ( J sc), open-circuit photovoltage ( V oc), fill factor (ff), and solar-light-to-electricity conversion efficiency ( η) were observed to be 54.5%, 6.22 mA cm −2, 0.53 V, 0.59, and 1.94%, respectively.

Device Operation of Conjugated Polymer/Zinc Oxide Bulk Heterojunction Solar Cells

AbstractSolar cells based on a poly(p‐phenylene vinylene) (PPV) derivative and zinc oxide nanoparticles can reach a power conversion efficiency of 1.6 %. The transport of electrons and holes in these promising devices is characterized and it is found that the electron mobility is equal to 2.8 × 10–9 m2 V–1 s–1, whereas the hole mobility amounts to 5.5 × 10–10 m2 V–1 s–1. By modeling the current–voltage characteristics under illumination it is found that the performance of PPV/zinc oxide solar cells is limited by the charge‐carrier mobilities. Subsequently, how to further improve the efficiency is discussed.

Nanocrystalline TiO2 Solar Cells Sensitized with InAs Quantum Dots

We report nanocrystalline TiO2 solar cells sensitized with InAs quantum dots. InAs quantum dots of different sizes were synthesized and incorporated in solar cell devices. Efficient charge transfer from InAs quantum dots to TiO2 particles was achieved without deliberate modification of the quantum dot capping layer. A power conversion efficiency of about 1.7% under 5 mW/cm2 was achieved; this is relatively high for a nanocrystalline metal oxide solar cell sensitized with presynthesized quantum dots, but this efficiency could only be achieved at low light intensity. At one sun, the efficiency decreased to 0.3%. The devices are stable for at least weeks under room light in air.

Hybrid polymer/metal oxide solar cells based on ZnO columnar structures

We focus on the preparation of hybrid polymer/zinc oxide (ZnO) solar cells, in which the metal oxide consists of ZnO columnar structures grown perpendicularly on a flat, dense “backing” layer, as a means to provide a direct and ordered path for photogenerated electrons to the collecting electrode. We used scanning electron microscopy, absorption spectroscopy and photovoltaic device measurements to study the morphology and device performance of the prepared structures. Different solution chemical routes were investigated for the synthesis of the inorganic device components, i.e. the ZnO columnar structures and the “backing” layers, which act as a seed-growth layer for the ZnO rods. The growth of the ZnO rods was dependent on the morphological and structural characteristics of the seed layer and moreover, the seed layer itself was also affected by the synthetic conditions for ZnO rod growth. Different polymers (high hole-mobility MEH-PPV based polymer and P3HT) were compared in these structures and power conversion efficiencies of 0.15 and 0.20% were achieved under 1 Sun illumination, respectively. Results are discussed in terms of the optoelectronic properties of the polymers.

Application of 9-substituted 3,4-perylenedicarboxylic anhydrides as sensitizers for zinc oxide solar cell

A series of 9-substituted 3,4-perylenedicarboxylic anhydrides were examined as sensitizers for the zinc oxide solar cell prepared by a one-step cathode deposition template method. The best performance was obtained for the bromo derivative. The incident photon-to-current efficiency (IPCE) at 431 nm, maximum short-circuit photocurrent density ( I sc), open-circuit photovoltage ( V oc), fill factor (ff), and solar-light-to-electricity conversion efficiency ( η) were observed to be 35.5%, 1.78 mA cm −2, 0.46 V, 0.64, and 0.52%, respectively.

Origin of Light-Harvesting Enhancement in Colloidal-Photonic-Crystal-Based Dye-Sensitized Solar Cells

The effect of the presence of a photonic crystal on the optical absorption of dye-sensitized titanium oxide solar cells is theoretically investigated herein. Different configurations in which a colloidal crystal can be implemented in such devices are modeled, and their absorptances compared. Experimental results on light-harvesting enhancement recently reported for periodically structured photoelectrodes are satisfactorily explained in terms of the appearance of multiple resonant modes localized in the absorbing layer when this is deposited onto one of the optical lattice surfaces. Longer matter-radiation interaction times for such frequencies result in higher absorption of those modes when compared to standard dye-sensitized solar cells. The effect of the finite size and the different characteristics of the photonic crystal on the optical absorption amplification effect is also discussed, new perspectives for colloidal-crystal-based photovoltaics being proposed.

Application of semisquaric acids as sensitizers for zinc oxide solar cell

A series of semisquaric acids were examined as sensitizers for the zinc oxide solar cell prepared by a one-step cathode deposition template method. Their cell performance was rather low due to high oxidation potential ( E ox) of semisquaric acids. However, the performance was improved by introducing long alkyl group on the nitrogen atom at the heteroaromatic moiety. A N-octadecylindolium derivative showed the best performance: the incident photon-to-current efficiency (IPCE) 38.0% at absorption maximum ( λ max) 423 nm, short circuit photocurrent density ( I sc) 1.116 mA cm −2, open circuit photovoltage ( V oc) 0.421 V, fill factor (ff) 0.57, and solar-light-to-electricity conversion efficiency ( η) 0.27%, respectively.

Charge Separation versus Recombination in Dye-Sensitized Nanocrystalline Solar Cells: the Minimization of Kinetic Redundancy

In this paper we focus upon the electron injection dynamics in complete dye-sensitized nanocrystalline metal oxide solar cells (DSSCs). Electron injection dynamics are studied by transient absorption and emission studies of DSSCs and correlated with device photovoltaic performance and charge recombination dynamics. We find that the electron injection dynamics are dependent upon the composition of the redox electrolyte employed in the device. In a device with an electrolyte composition yielding optimum photovoltaic device efficiency, electron injection kinetics exhibit a half time of 150 ps. This half time is 20 times slower than that for control dye-sensitized films covered in inert organic liquids. This retardation is shown to result from the influence of the electrolyte upon the conduction band energetics of the TiO2 electrode. We conclude that optimum DSSC device performance is obtained when the charge separation kinetics are just fast enough to compete successfully with the dye excited-state decay. These conditions allow a high injection yield while minimizing interfacial charge recombination losses, thereby minimizing "kinetic redundancy" in the device. We show furthermore that the nonexponential nature of the injection dynamics can be simulated by a simple inhomogeneous disorder model and discuss the relevance of our findings to the optimization of both dye-sensitized and polymer based photovoltaic devices.