Short-circuit Photocurrent Research Articles

Solanum nigrum and Eclipta alba leaf pigments for dye sensitized solar cell applications

The dye sensitized solar cells have been assembled by using natural dye extracted from Solanum nigrum and Eclipta alba. The solar cell constructed using the S. nigrum sensitized TiO2 photo-electrode exhibited a short-circuit photocurrent of 4.46 mA/cm2 and a power conversion efficiency of 0.77 % and that of E. alba sensitized TiO2 photo-electrode exhibited a short-circuit photocurrent of 4.04 mA/cm2 and a power conversion efficiency of 0.60 %. S. nigrum gave better photosensitization effect than E. alba and presents the prospect to be used as an environment-friendly, low-cost alternative system.

Effect of electropolymerization time on the performance of poly(3,4-ethylenedioxythiophene) counter electrode for dye-sensitized solar cells

Poly (3,4-ethylenedioxythiophene) (PEDOT) films were synthesized onto the fluorinated tin oxide (FTO) substrates as counter electrodes (CEs) for dye-sensitized solar cells (DSSCs) through an aqueous galvanostatic polymerization technique. Polymerization time was employed to control the surface morphologies and performances of the PEDOT films. The PEDOT electrodes showed faster reaction rate and higher electrocatalytic activity for I3− reduction as the polymerization time increased, which contributed to the increase of the open circuit voltage (VOC) for the DSSCs. The electrochemical impedance spectroscopy (EIS) indicated that charge transfer resistance (Rct) at CE/electrolyte interface decreased and then rebounded with the increasing polymerization time. Thus the short circuit photocurrent density (JSC) and fill factor (FF) of the DSSCs changed with the same trend. The energy conversion efficiency of the DSSC based on PEDOT CE up to 6.46% was achieved, which was higher than that based on Pt CE (6.33%). Therefore, the PEDOT film can be considered as a promising alternative CE for Pt-free DSSCs.

Characterization and photovoltaic performance of organic device based on CoMTPP/p-Si heterojunction

Hybrid organic/inorganic heterojunction of nanocrystalline 5,10,15,20-Tetrakis(4-methoxyphenyl)-21H,23H-porphine cobalt(II), (CoMTPP) and p-Si was fabricated by using the conventional thermal evaporation technique. The morphologies of the CoMTPP/p-Si were investigated by scanning electron microscopy (SEM). The dark current–voltage (I–V) characteristics of Au/p-CoMTPP/p-Si/Al heterojunction diode measured at different temperatures ranging from 298 to 423K have been investigated. Analytical approaches involving the thermionic emission and space charge limited currents (SCLC) were used to explain the I–V behavior in the forward bias. On the other hand, the carrier generation–recombination process limits the reverse current. The dependence of capacitance–voltage (C−2–V) for the device CoMTPP/p-Si was found to be almost linear which indicates that the junction behavior is abrupt nature and then the essential junction parameters were obtained. The performance of heterojunction showed a photovoltaic behavior with an open circuit voltage, Voc, of 0.283V, short circuit photocurrent ISC, of 0.433mA and power conversion efficiency, η of 3.6%.

Synthesis of new truxene based organic sensitizers for iodine-free dye-sensitized solar cells

Developing arylamine photosensitizers with high extinction coefficients, proper electronic structures, and steric properties is warranted for the dye-sensitized solar cells (DSCs) employing iodine-free redox shuttles. Two new organic sensitizers (M21 and M22) featuring unsymmetrical truxene-based triarylamine donor have been synthesized and compared to its reference sensitizer M4. The effects of unsymmetrical truxene-based triarylamine donors were investigated by their absorption spectra, electrochemical and photovoltaic properties. The incorporation of strong electron donor unit (i.e., dipropylfluorene and 4-methoxybiphenyl) has resulted in an improved light harvesting capacity, and thus photocurrent as well as efficiency of cells. M22 sensitized DSCs employing the Co(II/III)tris(1,10-phenanthroline)-based redox electrolyte affords a short circuit photocurrent of 13.1 mA cm−2, an open circuit voltage of 861 mV, and a fill factor of 0.70, corresponding to an overall conversion efficiency of 7.89% under standard AM 1.5 sunlight.

Tin Oxide Microspheres with Exposed {101} Facets for Dye‐sensitized Solar Cells: Enhanced Photocurrent and Photovoltage

Hierarchical SnO2 microspheres with exposed {101} facets are synthesized by a one-pot solvothermal reaction and explored as a scattering layer on top of a SnO2 nanoparticle film for dye-sensitized solar cells (DSCs). The microspheres not only enhance photon harvesting by effective light scattering/reflecting but also improve the energy level of the conduction band edge of the SnO2 photoanode, which leads to a simultaneous increase of the short-circuit photocurrent by 17% and open-circuit photovoltage by 20%. An improved overall conversion efficiency of 3.46% is achieved for DSCs using the SnO2 microspheres, which is the highest value reported so far for pure-SnO2 DSCs. Moreover, the SnO2 -microsphere DSCs exhibit a better photostability than the conventional TiO2 DSCs under simulated full sunlight.

Influence of indoline dye and coadsorbate molecules on photovoltaic performance and recombination in dye-sensitized solar cells based on electrodeposited ZnO

A detailed photoelectrochemical analysis of dye-sensitized solar cells based on electrodeposited porous ZnO, the indoline dye D149, cholic acid as optional coadsorbate, and a liquid iodide/triiodide electrolyte was performed. The effects of changes in the amount and chemical environment of the dye molecules on overall cell performance, distribution of trap states and recombination were studied. Short-circuit photocurrent, open-circuit photovoltage and cell efficiency improved with increasing amount of dye within the range investigated, while fill factors were lowered. The decline of the fill factor could be attenuated by coadsorbing cholic acid. Electrochemical impedance spectroscopy (EIS) was used to study the chemical capacitance, recombination resistance and series resistance in cells with different D149 loadings in the presence or absence of cholic acid. For increasing dye loading, the recombination parameter β and, in consequence, the recombination resistance around the maximum power point decreased, which explained the drop in the fill factors. In cells containing cholic acid, the conduction band edge was shifted upwards, the density of surface trap states was reduced, and the observed decrease of β was less pronounced compared to cells without coadsorbate. The charge transport in the electrolyte and the kinetics of charge transfer at the counter electrode were slowed down in cells with high dye content. A diode model accounting for non-linear recombination served to quantitatively link dye- and coadsorbate-induced changes in the voltage-dependence of the recombination resistance to the fill factor variation. Recombination with oxidized D149 molecules in aggregates and weak interaction between D149 and ZnO are discussed as physical origins of the observed trends.

ZnO nanoneedle/H2O solid-liquid heterojunction-based self-powered ultraviolet detector

ZnO nanoneedle arrays were grown vertically on a fluorine-doped tin oxide-coated glass by hydrothermal method at a relatively low temperature. A self-powered photoelectrochemical cell-type UV detector was fabricated using the ZnO nanoneedles as the active photoanode and H2O as the electrolyte. This solid-liquid heterojunction offers an enlarged ZnO/water contact area and a direct pathway for electron transport simultaneously. By connecting this UV photodetector to an ammeter, the intensity of UV light can be quantified using the output short-circuit photocurrent without a power source. High photosensitivity, excellent spectral selectivity, and fast photoresponse at zero bias are observed in this UV detector. The self-powered behavior can be well explained by the formation of a space charge layer near the interface of the solid-liquid heterojunction, which results in a built-in potential and makes the solid-liquid heterojunction work in photovoltaic mode.

Interplay between annealing temperature and optimum composition and fullerene aggregation effects in bulk heterojunction photocells based on poly(3-hexylthiophene) and unmodified C60

A lot of efforts have been devoted to synthesize novel fullerene derivatives to improve the performance of polymer-based bulk heterojunction photocells. Although the archetypical soluble fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is frequently treated as a reference material, PCBM, which carries both aromatic and aliphatic moieties, is not very simple molecule. In this context, unmodified C60, which is the simplest molecule among the C60-based fullerenes, seems to be the most suitable for the reference material. Here, a set of systematic experiments on the device performances of the bulk heterojunction composites consisting of P3HT and unmodified C60 over various compositions and annealing temperatures has been carried out. It has been found that the apparent optimum composition strongly depends on the annealing temperature chosen. Additionally, a monotonic relationship between the shift in the open-circuit voltage and the multiplication factor of the short-circuit photocurrent has been also found, directly indicating that the fullerene aggregation results in increased electron affinity to enhance the charge separation in the composites. The simple structure of the C60 molecule seems to contribute for maintaining the coherency in the present study.

Facile and Selective Synthesis of Oligothiophene-Based Sensitizer Isomers: An Approach toward Efficient Dye-Sensitized Solar Cells

Two sets of isomeric organic dyes with n-hexyl (DH and AH) or 2-ethylhexyl (DEH and AEH) groups substituted at the spacer part have been designed and straightforwardly synthesized via a facile and selective synthetic route. The structure difference between the isomers stands at the position of the incorporated alkyl chains which are introduced into the terthiophene spacer close to the donor (D) or anchor (A) side. The relationship between the isomeric structures and the optoelectronic properties are systematically investigated. It is found that, in the D series dyes, the alkyl group is much closer to the aromatic donor moiety, which brings about strong steric hindrance and therefore causes a remarkable twist in the molecular skeleton. In contrast, a more planar chemical structure and more effective π-conjugation are realized in the A series dye isomers. Consequently, the A series isomeric dyes demonstrate bathochromically shifted absorption bands, resulting in the improved light-harvesting capability and enhanced photo-generated current. However, the D series isomeric dyes with more twisted molecular skeleton have suppressed the intermolecular interactions and retarded the charge recombination more efficiently, which induces higher open-circuit photovoltage. Combining the two effects on the performance of the fabricated dye-sensitized solar cells (DSSC), the influence from the short-circuit photocurrent plays a more significant role on the power conversion efficiency (η). As a result, isomer AEH-based DSSC with quasi-solid-state electrolyte displays the highest η of 7.10% which remained at 98% of the initial value after continuous light soaking for 1000 h. Promisingly, a η of 8.66% has been achieved for AEH-based DSSC with liquid electrolyte containing Co(II)/(III) redox couple. This work presents the crucial issue of molecular engineering and paves a way to design organic sensitizers for highly efficient and stable DSSCs.

Investigation on the Photovoltaic Performance of ZnO Nanoarrays Prepared by Chemical Bath Deposition and Hydrothermal Method

ZnO nanorod arrays were successfully prepared by chemical bath deposition (CBD) and hydrothermal method (HTM), respectively. The photovoltaic performance of ZnO nanoarrays as photoelectrodes in dye-sensitized solar cells (DSCs) was investigated. Experimental results show that ZnO seed crystals prepared by a sol-gol process have c axis orientation and consist of nanoparticles within the range of 50~100nm. The same particle size and orientation is well preserved in ZnO nanoarrays grown on the seed crystal layers. The photovoltaic performance of DSCs based on ZnO nanoarrays as the photoelectrodes is poor, due to the weaker adsorption bond force between ZnO and dye, and lower dye adsorption quantity. By contrast, the DSCs composed of ZnO arrays prepared by hydrothermal method have optimal performance, the corresponding short circuit photocurrent density (Jsc), open circuit voltage (Voc), fill factor (FF) and photoelectric conversion efficiency (η) are 4.89 mA/cm2, 0.650V, 0.39 and 1.25 %, respectively.

Hydrothermal Preparation and Characterization of ZnO with Various Morphologies for Dye-Sensitized Solar Cells

Zinc oxide (ZnO) with various morphologies consisting of nanoparticles with a diameter of approximately 20 nm have been successfully prepared by hydrothermal method from zinc nitrate (Zn (NO3)2)/carbamide (CO(NH2)2) solution. The morphologies and phase structures of the as-prepared ZnO samples were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD). Results show that the morphologies of the as-prepared ZnO are successively present in broom-like, cabbage-like, chinese cabbage-like, honeycomb-like with the increase of the CO(NH2)2 concentration from 0.1 M to 1 M. The photovoltaic performances of dye-sensitized solar cells, based on ZnO with various morphologies as the photoelectrodes, are unobvious. With the morphologies of ZnO evolving, the short circuit photocurrent density (Jsc) increases from 2.35 to 3.72 mA/cm2, the fill factor (FF) increases from 0.400 to 0.570, and the corresponding conversion efficiency (η) varies from 0.520 % to 1.200 %. The low η may be due to the formation of the Zn2+/dye polymers.

Influence of highly efficient PbS counter electrode on photovoltaic performance of CdSe quantum dots-sensitized solar cells

PbS electrode with high catalytic activity to Sn 2− reduction certificated by the measurements of electrochemical impedance spectroscopy and cyclic voltammetry was prepared by a simple method. The high catalytic activity makes it be a low-cost alternative counter electrode to platinum (Pt) to be used in quantum dots-sensitized solar cells (QDSSCs) based on polysulfide electrolyte. The photovoltaic performance enhancement of the quantum dots (QDs)-sensitized semiconductor thin films due to the PbS counter electrode was evaluated by fabricating QDSSCs based on CdSe QDs-sensitized ZnO (SnO2) thin film. CdSe QDs-sensitized ZnO thin film has the lower internal total series resistance and electron transmission time, the higher electron lifetime and electron collection efficiency than the CdSe QDs-sensitized SnO2 thin film. Replacing the Pt counter electrode with the PbS counter electrode leads to more improvement on the short circuit photocurrent density for QDSSC based on the ZnO thin film than the SnO2 thin film. Therefore, the process to limit the photovoltaic performance of CdSe QDs-sensitized solar cell and the possible way to improve the photovoltaic performance were analyzed.

Synthesis and Photoelectrochemical Performance of Chalcogenopyrylium Monomethine Dyes Bearing Phosphonate/Phosphonic Acid Substituents

Chalcogenopyrylium monomethine dyes were prepared via condensation of a 4-methylchalcogenopyrylium compound with a chalcogenopyran-4-one bearing a 4-(diethoxyphosphoryl)phenyl substituent (or the phosphonic acid derivative). The dyes have absorbance maxima of 603-697 nm in the window where the solar spectrum is most intense. The dyes formed H-aggregates on TiO2, increasing the light-harvesting efficiency of the dyes. Shortcircuit photocurrent action spectra were acquired to evaluate the influence of dye structure on the photoelectrochemical performance.

Effect of a novel self-assembly based on coordination polymer with zinc porphyrin in supramolecular solar cells

Within this work, we firstly report the self-assemblies of zinc porphyrin coordination polymers (CPs) appended isonicotinic acid ligands by metal–ligand axial coordination approach immobilized on the nanostructured TiO2 electrode surfaces in photoelectrochemical devices. Compared to the assemblies based on zinc porphyrins integrated isonicotinic acid ligands via metal–ligand axial coordination or metal–ligand edged binding approach, the CPs-based assemblies exhibit significantly improved photovoltaic performances. Especially, the assembly based on iminazole-substituted zinc porphyrin coordination polymer exhibits an excellent photovoltaic performance with a short circuit photocurrent density (Jsc) of 3.8mAcm−2, an open circuit voltage (Voc) of 0.31V, a fill factor (FF) of 0.67 and an overall conversion efficiency (η) of 0.48% under AM 1.5 conditions. The results serve as another good testing ground for the fabrication of supramolecular devices techniques in future.

Efficient solar water splitting by enhanced charge separation in a bismuth vanadate-silicon tandem photoelectrode

Metal oxides are generally very stable in aqueous solutions and cheap, but their photochemical activity is usually limited by poor charge carrier separation. Here we show that this problem can be solved by introducing a gradient dopant concentration in the metal oxide film, thereby creating a distributed n(+)-n homojunction. This concept is demonstrated with a low-cost, spray-deposited and non-porous tungsten-doped bismuth vanadate photoanode in which carrier-separation efficiencies of up to 80% are achieved. By combining this state-of-the-art photoanode with an earth-abundant cobalt phosphate water-oxidation catalyst and a double- or single-junction amorphous Si solar cell in a tandem configuration, stable short-circuit water-splitting photocurrents of ~4 and 3 mA cm(-2), respectively, are achieved under 1 sun illumination. The 4 mA cm(-2) photocurrent corresponds to a solar-to-hydrogen efficiency of 4.9%, which is the highest efficiency yet reported for a stand-alone water-splitting device based on a metal oxide photoanode.

Photovoltaic performance of bithiazole-bridged dyes-sensitized solar cells employing semiconducting quantum dot CuInS2 as barrier layer material

In this work, the quantum dot CuInS2 layer was deposited on TiO2 film using successive ionic layer absorption and reaction (SILAR) method, and then two bithiazole-bridged dyes (BTF and BTB) were sensitized on the CuInS2/TiO2 films to form dye/CuInS2/TiO2 photoanodes for DSSCs. It was found that the quantum dots CuInS2 as an energy barrier layer not only could effectively improve open-circuit voltage (Voc) of solar cell, but also increase short-circuit photocurrent (Jsc) compared to the large decrease in Jsc of ZnO as energy barrier layer. The electrochemical impedance spectroscopy (EIS) measurement showed that the CuInS2 formed a barrier layer to suppress the recombination from injection electron to the electrolyte and improve open-circuit voltage. Finally, the open-circuit voltage increased about 22 and 27mV for BTF and BTB-/CuInS2/TiO2-based cells, the overall conversion efficiencies also reached to 7.20% and 6.74%, respectively.

Efficiency enhancement in dye sensitized solar cells based on PAN gel electrolyte with Pr4NI + MgI2 binary iodide salt mixture

The effect of using a binary iodide salt mixture in N719 dye-sensitized TiO2 solar cells (DSSCs) is investigated. The cells use tetrapropylammonium iodide (Pr4NI) and magnesium iodide (MgI2) in a plasticized polyacrylonitrile gel in glass/FTO/nano-porous TiO2/gel, I-2/Pt/FTO/glass solar cell structure. The salt composition in the gel electrolyte is varied to optimize the efficiency of DSSCs. The DSSCs with MgI2 or Pr4NI as the only iodide salt showed the efficiencies 2.56 and 4.16 %, respectively, under AM 1.5 (100 mW cm(-2)) illumination while the DSSC with mixed cations with 18.4:81.6 MgI2:Pr4NI molar ratio shows the highest efficiency of 5.18 %. Thus the efficiency enhancement, relative to the high efficiency end member is about 25 %. DC polarization measurements establish the predominantly ionic behavior of the electrolytes, and show that the variation of efficiency with salt composition correlates with the change in short circuit photocurrent density (J (sc)), which appears to be governed by the iodide ion conductivity. It is also found that J (sc) correlates with the iodide ion transference number estimated from DC polarization data taken with non-blocking iodine electrodes. This study suggests that binary iodide mixtures may be used to obtain efficiency enhancement in different types of DSSCs based on polymeric, gel, or solvent electrolytes.

Interfacial polymer ferroelectric dipole induced electric field effect on the photovoltaic performance of organic solar cells

Effect of a dipolar electrical field on the photovoltaic properties of polymer solar cell devices in the bulk heterojunction structure based on 1:1 blend of donor-regioregular poly(3-hexylthiophene), P3HT, and acceptor-phenyl-C61-butyric acid methyl ester, PCBM, polymer semiconductor material is studied. With a thin layer of poled ferroelectric P(VDF + TrFE) copolymer film having oriented dipoles inserted at the interface between poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) and the P3HT:PCBM composite layer, significant improvement in the short-circuit photocurrent and open circuit voltage was observed consistent with the increase in the poling voltage. Remnant polarization charge due to dipoles produces localized electric field of 300–700 V · μm−1. The presence of the electric field helps increase the charge transfer exciton dissociation rates at the P3HT (donor)–PCBM (acceptor) interfaces, reduces the exciton recombination probability and increases the carrier extraction yield resulting in the enhancement in the photocurrent. Solar cell device in a structure having a poled P(VDF + TrFE) copolymer film sandwiched between the two P3HT:PCBM composite layers shows only a marginal improvement in the photovoltaic properties. This is mainly attributed to shielding of dipolar field from free charge carries and the inferior nanoscale morphology of the P3HT:PCBM composite layer.

Deposition of Cu<sub>2</sub>ZnSnS<sub>4</sub> Thin Film by Pulsed Laser Deposition and Assembly of Thin Film Solar Cell with the Novel Structure of FTO/CdS/Cu<sub>2</sub>ZnSnS<sub>4</sub>/Mo

Cu2ZnSnS4(CZTS) thin film was successfully prepared by pulsed laser deposition using CZTS nanocrystal as a source and the thin film solar cell with the novel structure of FTO/CdS/CZTS/Mo was assembled. At the laser incident energy of 6 J·cm-2, the chemical composition of the CZTS thin film was Cu1.74Zn0.80Sn1.00S4.04,near to stoichiometric ratio. The thin film solar cell with the novel structure of FTO/CdS/CZTS/Mo gave short circuit photocurrent density of 1.01 mA·cm-2, open circuit voltage of 0.39 V, and fill factor of 0.485, corresponding to the photoelectric conversion efficiency of 0.19% at the illumination (Air Mass 1.5, 100 mW·cm-2).

Layer-by-Layer Growth and Photocurrent Generation in Metal–Organic Coordination Films

A series of metal–organic coordination films with tetra(4-carboxyphenyl)porphyrin (TCPP) and trimesic acid (TMA) ligands and Cu2+ ion linkers were grown layer-by-layer on TiO2-modified indium tin oxide electrodes and the cathodic short-circuit photocurrent that they generate was studied. The layer-by-layer growth was verified by using absorption spectroscopy in the visible and X-ray photoelectron spectroscopy, highlighting the consistent coverage of TCPP in each layer. The photocurrent increases nonlinearly with the number of TCPP layers and with the number of TMA layers introduced as a buffer between TCPP and substrate. These observations are rationalized by considering substrate screening of the TCPP photoexcited state and charge transport across the metal–organic multilayers.