Short-circuit Photocurrent Research Articles

Nanoarchitecture of variable sized graphene nanosheets incorporated into three-dimensional graphene network for dye sensitized solar cells

A novel three-dimensional (3D) nanoarchitecture consisting of hybrid graphene nanosheets (GNs)/graphene foam (GF) was fabricated on the FTO conducting substrate as a high efficient counter electrode (CE) for dye sensitized solar cells (DSSCs). The GNs with various sized such as large-sized heat-reduced graphene nanosheets (H-GNs) and small-sized laser-reduced graphene quantum dots (L-GQDs) were synthesized and used as catalytic materials incorporated into a 3D GF network, respectively. In this design, the aggregations and restacking of GNs were efficiently reduced, which is beneficial for increasing the amount of the active defective sites at the edges of graphene to the electrolyte solution. Especially, L-GQDs with smaller dimension less than 100nm have more active defective sites at edges, providing superiority over the large-sized H-GNs in terms of electrocatalytic activity. Meanwhile, the GF network with high conductivity provides fast electron transport channels for charge injection between the GNs and FTO. The DSSC with this hybrid CE exhibited energy conversion efficiency (η) of 7.70% with an open circuit voltage (VOC), short circuit photocurrent density (JSC) and fill factor (FF) of 760mV, 15.21mAcm−2, and 72.0%, respectively, which is comparable to that of the conventional Pt CE (7.68%).

Investigation of effect of anti-aggregation agent on the performance of nanostructure dye-sensitized solar cells

AbstractDye sensitized solar cells (DSSCs) based on indigo dyes exhibit suitable conversion efficiency. These organic dyes have been undergone for aggregation. Electron transfer process is reduced due to an aggregation of molecular dyes. Therefore, anti-aggregation agent is commonly utilized in fabrication of DSSCs. In the present study, two anti-aggregation agents namely as 3α,7α-dihydroxy-5β-cholanic acid (cheno) and 3α,7α,12α-trihydroxy-5β-cholanic acid (cholic acid) were added to indigo dye solution in DSSCs in order to determine the photovoltaic parameters such as short circuit photocurrent, open circuit voltage and conversion efficiency of each individual dye in the absence and presence of anti-aggregation agents. The results show that the conversion efficiencies are improved with reduced aggregation. Spectrophotometric evaluations of the indigo dyes in solution and on a TiO

Effect of crystallinity and morphology of TiO2 nano-structures on TiO2:P3HT hybrid photovoltaic solar cells

A comparative study has been made of hybrid solar cells based on poly(3-hexylthiophene) (P3HT) and different nano-structures of TiO2. Electrospinning, which is a low cost production method for large area nanofibrous films, was employed to fabricate TiO2 nanofibers and spin coating method was employed to fabricate organic-inorganic hybrid solar cells based on P3HT and TiO2 nanostructures. The performance of the hybrid solar cells was analyzed for four density levels of the TiO2 nanostructure. It was found that higher densities of TiO2 leads to more interface area and generates excitons, so that the power conversion efficiency increases to 0.13. TiO2 nanoparticles with power conversion efficiency of 0.15 showed better performance than TiO2 nanofibers because of greater interface area. Also the crystallinity effect of the TiO2 nanostructure on solar cell performance was investigated. Moreover, an improved photovoltaic performance was achieved after the interface modification, and the highest conversion efficiency was obtained from the N719 modified device at 241 nm, short-circuit photocurrent (J sc) of 3.88 mA cm−2, open-circuit voltage (V oc) of 0.09 V and fill factor of 0.16; so that an overall conversion efficiency (η) of 0.35% was obtained.

Formate dehydrogenase catalyzedCO2reduction in a chlorin-e6sensitized photochemical biofuel cell

The new visible-light operated CO2-glucose biofuel cell consisting of chlorin-e6immobilized on TiO2thin layer film onto optical transparent conductive glass electrode (OTE) as an anode, formate dehydrogenase (FDH) and viologen with long alkyl chain co-immobilized OTE as a cathode, and the solution containing glucose, glucose dehydrogenase (GDH) and NAD+as a fuel was developed. The short-circuit photocurrent and the open-circuit photovoltage of this cell are 37 μA.cm-2and 390 mV, respectively. The maximum power is estimated to be 57 μW.cm-2. The overall photoenergy conversion efficiency is estimated to be 0.057%. After 2 h irradiation to this cell, 0.65 μmol of formic acid was produced. During irradiation, the photocurrent was constant value of 32 ± 10 μA.cm-2in the cell. Thus, CO2reduces and formic acid produces while generating electricity with visible light irradiation to this biofuel cell.

Enhancing the optical absorption of anthocyanins for dye-sensitized solar cells

This work presents our investigation on natural dyes extracted from the skin of Eggplant, Red Cabbage, and Red Onion as sensitizers for fabrication of dye-sensitized solar cells (DSSCs) and the conditions that could maximize their performance. We investigated the influence of various factors in the extraction process, such as various solvents, influence of acidification, or basification on the extraction solution, solution concentration on UV-VIS patterns absorption spectra of the anthocyanins, and the influence of these parameters on the performance of DSSCs. It was found that we could considerably enhance the optical absorptivity of natural sensitizers and consequently the performance of DSSCs. Overall performance of natural dyes as sensitizers in DSSCs was evaluated in terms of short circuit current and open circuit voltage. Short circuit photocurrent densities (JSC) up to 6.14 mA/cm2, and open circuit voltage (VOC) ranging from 0.29 to 0.66 V, were obtained from the natural sensitizers.

Engineering of the electron donor of triarylamine sensitizers for high-performance dye-sensitized solar cells

Triphenylamine (TPA) and their derivatives are well-known electron-rich compounds that are widely used in various optical and electronic fields. Here, two new organic dyes (M40 and M41) featuring TPA or dihexyloxy-substituted triphenylamine (DHO–TPA) electron donor have been designed and synthesized. M40 sensitized DSCs employing the Co(II/III)tris(1,10-phenanthroline)-based redox electrolyte affords a short circuit photocurrent of 14.32mAcm−2, an open circuit voltage of 907mV, and a fill factor of 0.68, corresponding to an overall conversion efficiency of 8.83% under standard AM 1.5 sunlight. This efficiency is much higher than those of the M41 sensitized DSCs, being 7.81% under the same conditions. Absorption spectra, electrochemical measurements, theoretical calculations, and photovoltaic measurements are used to compare the light absorptions, energy-levels, and charge transfer dynamics that contribute to the photovoltaic behavior.

Photovoltaic property of domain engineered epitaxial BiFeO3 films

The effect of domain structure on the photovoltaic response of BiFeO3 vertical capacitors is investigated, by domain engineering using vicinal SrTiO3 substrates. It is observed that the open-circuit photovoltage remains unaffected by the domain structure, consistent with the photovoltaic effect being driven by the polarization modulated band bending at the metal/BiFeO3 interface. Nevertheless, the enhancement of short-circuit photocurrent is achieved and attributed to the conducting domain walls. Furthermore, we have estimated and compared the magnitudes of photoconductivity of domains and domain walls in BiFeO3 thin films, which can be used to explain the photocurrent improvements. These findings cast some light on the role of domain walls in ferroelectric photovoltaic effects and provide a simple route towards enhanced efficiency.

Synthesis and characterization of novel carbazole-based terpyridyl photosensitizers for dye-sensitized solar cells (DSSCs)

Two novel terpyridyl-based Ru(II) complexes, DH-1 and DH-2, were synthesized and characterized as photosensitizers for dye-sensitized solar cells. To enhance the thermal and photostability, a strong electron donor bidentate carbazole-based ancillary ligand was molecularly engineered and used to replace two monodentate labile isothiocyanates. Photovoltaic characterizations, I–V curve and IPCE, of DH-1 and DH-2 were carried out in presence of deoxycholic acid as an additive to determine the best device working conditions. DH-1 showed IPCE of 45% at 540 nm, short circuit photocurrent density (Jsc) of 11.69 mA cm−2, open circuit photovoltage (Voc) of 0.64 V, fill factor of 0.63, producing an overall conversion efficiency (η) of 4.68%, where DH-2 showed IPCE of 45% at 540 nm, Jsc of 10.90 mA cm−2, Voc of 0.59 V and FF of 0.59, which translated into η of 3.82%. DFT calculations rationalized the light harvesting efficiency and charge separation of why DH-1 > DH-2.

Novel D–π–A structured porphyrin dyes containing various diarylamino moieties for dye-sensitized solar cells

A series of novel zinc porphyrins which are featured with a donor–π–acceptor structure have been synthesized for use in the dye-sensitized solar cells. Various diarylamine moiety, such as diphenylamine, iminodibenzyl or iminostilbene, is introduced at porphyrin meso position as an electron donating group. The cell fabricated with the iminodibenzyl-substituted porphyrin sensitizer yields a short circuit photocurrent density of 9.68 mA/cm2, an open-circuit voltage of 740 mV, and a fill factor of 73.48%, corresponding to an overall conversion efficiency (η) up to 5.26%, which is greater than those obtained by diphenylamine- and iminostilbene-substituted porphyrin-sensitized solar cells (η = 4.05% and 2.62%, respectively). The theoretical studies reveal that the iminodibenzyl donor has the strongest electron donating ability among all three diarylamine substituents employed, which is believed to play a significant role in influencing the photovoltaic properties of these sensitizer-based solar cells.

Optical modeling of bulk-heterojunction organic solar cells based on squarine dye as electron donor

The potentiality of a squarine dye (Sq1) for using as electron donor component in bulk heterojunction organic solar cells (BHJ) has been studied from the optical point of view. The soluble n-type fullerene, (6,6)-phenyl C61 butyric acid methyl ester (PC61MB) was chosen as acceptor. Optical modelling based on transfer matrix method was carried out to predict and improve photovoltaic performance of a BHJ device with blended Sq1/PC61MB active layer. The dependence of the absorption and the calculated maximum short circuit photocurrent (Jscmax) on the thickness of the active layer (dact), was investigated for two weight ratios of Sq1 and PC61MB. Thus, the optimal dact was calculated to be about 100 nm, which provides an efficient overlapping of the total absorption with solar spectrum in the range between 580 and 900 nm. Besides, it is found that the insertion of ZnO or C60 spacer layer shifts Jscmax peak to lower dact and significantly enhances Jscmax for active layers with dact < 50 nm, which is mainly due to improved light absorption by a factor of 5 to 10. Simultaneously, for dact <100 nm the optical effect of inserted PEDOT:PSS hole transporting layer is negligible.

Increased photovoltaic performance by the optimized TiClI4 and AlCl3 surface treatment in dye-sensitized solar cells.

The surface of TiO2 photoelectrodes coated on F-doped SnO2 (FTO) was modified by soaking it in a TiCl4:AlCl3 mixed aqueous solution with various molar ratios, and then calcining to produce the TiCl4:AlCl3-treated TiO2 photoelectrode (Ti:Al-TiO2/FTO). The highest power conversion efficiency (PCE) was obtained from dye-sensitized solar cells (DSSC) with Ti:Al(5:5)-TiO2/FTO, which was prepared from the mixed solution with the molar ratio of 5:5 (TiCi4:AlCl3). PCE of DSSC with Ti:Al (5:5)-TiO2/FTO was improved by ca. 19.6%, compared to that of the reference device with Ti:Al (10:0)-TiO2/FTO (i.e., TiO2-coated TiO2/FTO) due to an enhancement in both short-circuit photocurrent (J(sc)) and open-circuit voltage (V(oc)). A series of measurements such as UV-visible absorption, electrochemical impedance, open circuit voltage decay and dark current revealed that the increase in J(sc) was attributed to the improvement of electron collection efficiency by a prolonged electron lifetime, and the suppression of the charge recombination between injected electrons and I3(-) ions was found to increase the V(oc) value of the device with Ti:Al(5:5)-TiO2/FTO.

CdS/CdSe co-sensitized TiO2 nanowire-coated hollow Spheres exceeding 6% photovoltaic performance

The development of an effective anode material with hierarchical multi-dimensional architecture is conducive to further improve the cell performance of photovoltaic devices. Herein we introduce an intriguing three-dimensional (3D) hierarchically branched hollow sphere-nanowire hybrid TiO2 photoanode for promising CdS and CdSe quantum dots co-sensitized solar cells application. The demonstrated 3D hierarchically hybrid photoanode owns a considerably high specific surface area while maintaining roomy space and providing ample porosity for efficient electrolyte infiltration. Moreover, the outstanding light scattering ability of such multi-dimensional architecture leads to an enhancement of light utilization efficiency and thus significantly enhanced short-circuit photocurrent. The control over the pore size of TiO2 hollow spheres and the optimizations on the newly developed chemical bath deposited (CBD) cuprous sulfide (Cu2S)/FTO counter electrode eventually yields power conversion efficiency as high as 6.01% for CdS/CdSe based quantum dot-sensitized solar cells (QDSSCs).

N-type Cu2O Film for Photocatalytic and Photoelectrocatalytic Processes: Its stability and Inactivation of E. coli

Photoelectrocatalytic (PEC) inactivation of Escherichia coli K-12 by cuprous oxide (Cu2O) film irradiated by visible light is firstly reported. A complete inactivation of about 7 log of E. coli was obtained for Cu2O film within 6 h. The bacterial inactivation efficiency was significantly improved in a photoelectrochemical cell, in which 7 log of E. coli could be completely inactivated within 2 h by Cu2O film with a 0.1 V bias. Electric charge transfer between electrodes and E. coli, and electric charge inactivation towards E. coli were investigated using membrane-separated reactor combined with short circuit photocurrent technique. H2O2, hole, and toxicity of Cu2O film were found responsible for the inactivation of E. coli. Toxicity of copper ions (including Cu2+ and Cu+) leakage from Cu2O films was determined and the results showed that the amount of leakage copper ions was not toxic to E. coli. Finally, the Cu2O film was proved to be effective and reusable for PC and PEC inactivation of E. coli.

A-Si:H/µc-Si:H tandem junction based photocathodes with high open-circuit voltage for efficient hydrogen production

Abstract

Graphene nanosheets@ZnO nanorods as three-dimensional high efficient counter electrodes for dye sensitized solar cells

Graphene nanosheets@ZnO nanorods as a three-dimensional high efficient counter electrode for dye sensitized solar cells is described, highlighting the ZnO nanorods as a 3D framework nanostructure for preventing the aggregations of GNs. It is demonstrated that, when the nanohybrids are used as CE materials for DSSCs, compared to their pristine GNs, the GNs@ZnO nanorod hybrids without aggregations of GNs have a significant improvement in catalytic performance toward the reduction of triiodide, which were reflected in their electrochemical properties such as high current density, narrow peak-to-peak separation (EPP) and low charge transfer resistance (RCT). The enhancement of electrochemical performance can be attributed to more active defective sites at the edges of GNs and the reduction of the restacking of GNs due to the 3D ZnO nanorod nanostructure. The DSSC with this hybrid CE exhibited energy conversion efficiency (η) of 8.12% with an open circuit voltage (VOC), short circuit photocurrent density (JSC) and fill factor (FF) of 765mV, 21.7mAcm−2, and 67.1%, respectively, which is comparable to that of the conventional Pt CE (8.82%).

CdS nanoflake arrays for highly efficient light trapping.

CdS nanoflake arrays (NFAs) exhibit unprecedented light absorption capability, and they can serve as a scaffold to load thin organic absorbers for extraordinarily high light absorption. As a result, the hybrid solar cell consisting of NFAs and organic absorber yields a ten-times high short-circuit photocurrent compared to the counterpart device with a common planar structure.

Investigation of the influence of coadsorbent dye upon the interfacial structure of dye-sensitized solar cells.

The interface between Ru(tcterpy)(NCS)3TBA2 [black dye (BD); tcterpy = 4,4',4″-tricarboxy-2,2':6',2″-terpyridine, NCS = thiocyanato, TBA = tetrabutylammonium cation] and nanocrystalline TiO2, as found in dye-sensitized solar cells, is investigated by soft-X-ray synchrotron radiation and compared with the adsorption structure of cis-Ru(Hdcbpy)2(NCS)2TBA2 (N719; dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) on TiO2 to elucidate the relationship between the adsorption mode of BD and the photocurrent with and without coadsorbed indoline dye D131. The depth profile is characterized with X-ray photoelectron spectroscopy and S K-edge X-ray absorption fine structure using synchrotron radiation. Both datasets indicate that one of the isothiocyanate groups of BD interacts with TiO2 via its S atom when the dye is adsorbed from a single-component solution. In contrast, the interaction is slightly suppressed when D131 is coadsorbed, indicated by the fact that the presence of D131 changes the adsorption mode of BD. Based upon these results, the number of BD dye molecules interacting with the substrate is shown to decrease by 10% when D131 is coadsorbed, and the dissociation is shown to be related to the short-circuit photocurrent in the 600-800 nm region. The design of a procedure to promote the preferential adsorption of D131 therefore leads to an improvement of the short-circuit current and conversion efficiency.

Design and electrical characterization of Au/Anthracene/p-Si/Al organic/inorganic heterojunction

Hybrid organic/inorganic heterojunction of nanocrystalline Anthracene and p-Si was fabricated by using a conventional thermal evaporation technique. The crystal and molecular structure of the Anthracene thin films were analyzed by means of X-ray diffraction (XRD), and Fourier Transformation-Infra Red (FT-IR) spectroscopy. The morphologies of the Anthracene/p-Si were investigated by scanning electron microscopy (SEM). The dark current–voltage (I–V) characteristics of Au/Anthracene/p-Si/Al heterojunction were investigated at room temperature (293K). The calculated series resistance and the shunt resistance of the device were found to be 440Ω and 1.47MΩ, respectively. The Cheung–Cheung and Norde’s models were used to investigate and determine the heterojunction parameters. The ideality factor and barrier height values of the Au/Anthracene/p-Si/Al diode were obtained to be 1.1 and 0.464eV, respectively. The dependence of capacitance–voltage (C−2–V) for the device Anthracene/p-Si was found to be almost linear. Essential junction parameters and performance of heterojunction established a photovoltaic behavior with an open circuit voltage (Voc) 0.382V, short circuit photocurrent (ISC) 0.72mA and power conversion efficiency (η) of 4.65%.

Surface modification of dye-sensitized solid-state solar cells by atmospheric-pressure plasma jet

Surface treatment of dye-sensitized solid-state solar cells (DSSSCs) by an atmospheric-pressure plasma jet was carried out to improve the characteristics of DSSSCs using Ar/O2 as a process gas. This is a dry process and a low energy consumption method for the surface modification of DSSSCs owing to the easy generation of plasma at atmospheric pressure. Active species and radicals were generated by the atmospheric-pressure plasma jet to modify the TiO2 surface in the DSSSCs. The important parameters of DSSSCs, such as the short circuit photocurrent density (JSC) and the open circuit photovoltage (VOC), were measured using the solar cell evaluation system. The surface condition of DSSSCs was analyzed by X-ray photoelectron spectroscopy (XPS), ultraviolet visible absorption spectroscopy (UV-VIS), and scanning electron microscopy (SEM). As a result, the solar conversion efficiency of DSSSCs increased to 1.96% from 1.60% after 15 min of dry plasma treatment.

Enhancement of pyroelectric signal by continuous ultraviolet illumination of epitaxial Pb(Zr0.2Ti0.8)O3 films

The pyroelectric signal generated by an epitaxial Pb(Zr0.2Ti0.8)O3 film can be enhanced by continuous illumination with ultraviolet (UV) light. The measured signal increases more than 2 times at low modulation frequencies of the incident infrared (IR) radiation (∼10 Hz) and at wavelengths where the short-circuit photocurrent presents the maximum value (∼280–300 nm). The tentative explanation is that the changes in polarization induced by the temperature variation under modulated IR illumination are generating a variable internal electric field, able to collect the photogenerated carriers produced under continuous UV illumination leading to an additional signal in phase with the pyroelectric one. This finding could be exploited for designing pyroelectric detectors with enhanced characteristics by combining both UV and IR responses.