High-performance Dye-sensitized Solar Cells Research Articles

Sandwich-like octahedral cobalt disulfide/reduced graphene oxide as an efficient Pt-free electrocatalyst for high-performance dye-sensitized solar cells

A novel sandwich-like hierarchical structure composed of reduced graphene oxide (RGO) and uniform cobalt disulfide (CoS2) octahedrons is successfully prepared by a simple one-step solvothermal process, in which Co2+ cations attracted into graphene framework by the electrostatic adsorption induce the growth of octahedral CoS2 nanoparticles between the layers of graphene. The fascinating sandwich-like structured CoS2/RGO hybrid inherits excellent electrical conductivity of graphene skeletons. Meanwhile, CoS2 octahedrons intercalated between the layers of graphene provide both rich inner active sites for the reduction of triiodide and abundant mesoporous structure for effective electrolyte diffusion. Benefit from the synergistic effects of CoS2 octahedrons and RGO, the dye-sensitized solar cell (DSSC) assembled with this CoS2/RGO counter electrode (CE) manifests excellent photoelectric conversion efficiency (7.69%), even higher than that of DSSC with conventional noble metal Pt CE (7.38%). Furthermore, CoS2/RGO composite displays outstanding electrochemical stability in I3−/I− redox electrolyte. Overall, this design provides a new strategy for the development of alternative Pt-free counter electrode materials in a DSSC system.

Three-dimensional porous vanadium nitride nanoribbon aerogels as Pt-free counter electrode for high-performance dye-sensitized solar cells

Three-dimensional (3D) porous vanadium nitride nanoribbon aerogels (PVNNRAs) are prepared by hydrothermal synthesis and subsequent nitridation in ammonia/argon atmosphere and investigated as Pt-free counter electrode in dye-sensitized solar cells (DSCs). 3D porous nanoribbon aerogel can simultaneously offer more electrocatalytic active sites, a fast electron-transport pathway, and a favorable electrolyte diffusion channel, which endows the PVNNRA electrode with high electrocatalytic activity for the reduction of I3−. Under full-sun illumination (AM 1.5, 100mWcm−2), the DSC fabricated with PVNNRA counter electrode achieves a conversion efficiency of 7.05%, which is comparable to that of DSCs fabricated with Pt counter electrode. In addition, the PVNNRA electrode exhibits good stability in I−/I3− redox electrolyte. Thus, 3D PVNNRAs can be considered as a cost-effective alternative to Pt as the counter electrode of DSCs.

Electropolymerized polyaniline/graphene nanoplatelet/multi-walled carbon nanotube composites as counter electrodes for high performance dye-sensitized solar cells

Polyaniline (PANI)/graphene nanoplatelet (GNP)/multi-walled carbon nanotube (MWCNT) composite films deposited on fluorine-doped tin oxide (FTO) substrates were successfully fabricated through electrochemical method without pre-treatment of GNP and MWCNT to provide a lower cost counter electrode (CE) for dye-sensitized solar cells (DSSCs). By varying the contents of GNP and MWCNT in the PANI composite CE, the short-circuit current density of DSSC was found to linearly relate to the reduction current density of I−/I3− redox couples measured by cyclic voltammetry. The open-circuit voltage (VOC) is also highly dependent on the reduction potential of redox couples. Besides, the charge transfer resistance at the electrolyte/CE interface measured by electrochemical impedance spectroscopy has an approximately linear relationship with the sheet resistance of PANI composite CE. Notably, the DSSC with the CE fabricated by the weight ratio of PANI/GNP/MWCNT at 1:0.003:0.0045 yielded the highest power conversion efficiency of 7.67±0.05%, which is comparable with the conventional Pt cell (7.62±0.07%).

Benzimidazole/Pyridoimidazole-Based Organic Sensitizers for High-Performance Dye-Sensitized Solar Cells.

A new series of benzimidazole (BIm)-based dyes (SC32 and SC33) and pyridoimidazole-(PIm) based dyes (SC35, SC36N and SC36) were synthesized as sensitizers for dye-sensitized solar cells (DSSCs). The N-substituent and C-substituent at the BIm and PIm cores were found to be the dominating factor in determining the electronic properties of the dyes and their DSSCs performance. The efficiency of BIm-based dyes (SC35 and SC36) was found to be higher than that of the PIm-based dyes (SC32 and SC33) due to better light harvesting. The C-substituents in SC36, a 4-hexylloxybenzene and a hexyl chain, are beneficial to dark current suppression, and hence SC36 achieves the best efficiency of 7.38 % (≈85 % of N719). The two BIm dyes have better cell efficiencies than their congeners with a bithiophene entity between the BIm and the anchor due to better light harvesting of the former.

Synergistic effect of TiO2 hierarchical submicrospheres for high performance dye-sensitized solar cells

The performance of dye-sensitized solar cells (DSCs) could be improved by using rationally designed mesoporous film structure for electron collection, dye adsorption and light scattering. The development of a novel double layer film prepared by TiO2 hierarchical submicrospheres and nanoparticles was reported in this article. The submicrospheres were composed of rutile nanorods of 10 nm diameter and the length of 150–250 nm, which facilitated fast electron transport, charge collection and light scattering. Using a double layer structure consisting of the 10 wt% film as a dye loading layer and the 50 wt% film as the light scattering layer, C101 sensitizer and liquid electrolyte, DSC yielded power conversion efficiency of 9.68% under 1 sun illumination.

Comparative study of N719 dye on two different photo-anodes

Nano-composites of TiO2 and ZnO were successfully prepared using the doctor blade application and high temperature sintering on indium-doped tin oxide (ITO) glass substrate. They were used as efficient photo anode in high performance dye-sensitized solar cells (DSSCs) assembled with N719 dye. The high-density frameworks of TiO2 and ZnO were synthesized on separate ITO conducting glass using a facile and cost-effective two-step approach to compare the output efficiency. We report on the interfacial boundary relationships, charge – collection conversion efficiency and I-V characteristics of the DSSCs with different electrolytes. The TiO2 photo anode demonstrated an enhanced solar-to-electrical energy conversion of approximately 5.41 % with KCl electrolyte which was far less than that of a ZnO photo anode with KCl electrolyte which had about 21 % increase under conditions of 1.5 AM. Because of the enhanced solar energy conversion of the ZnO photo anode, l.arboreus with KI sensitizer records 9.78 % is a promising candidate for large manufacture of high performance DSSCs modules.

Transparent Conductive Oxide Films for High-Performance Dye-Sensitized Solar Cells

In this paper, atmospheric pressure chemical vapor deposition of fluorine-doped tin oxide (FTO) thin films of various thicknesses and dopant levels is reported. The deposited coatings are used to fabricate dye-sensitized solar cells, which exhibited reproducible power conversion efficiencies in excess of 10%. No surface texturing of FTOs or any additional treatment of dye-covered films is applied. In comparison, the use of commercial FTOs showed a lower cell efficiency of 7.11%. Detailed analysis showed that the cell efficiencies do not simply depend on the resistivity of FTOs but instead rely on a combination of carrier concentration, thickness, and surface roughness properties.

High-Performance Porphyrin-Based Dye-Sensitized Solar Cells with Iodine and Cobalt Redox Shuttles.

Recently, enormous research passion has been devoted to enhance the power conversion efficiency (PCE) of porphyrin sensitizers for dye-sensitized solar cells (DSSCs), but the major stumbling block is the absorption defect in the visible-light region. To address this challenge, high-performance DSSCs are reported based on a new donor-π-acceptor sensitizer FW-1, 7H-dibenzo[c,g]carbazole-substituted and fused zinc porphyrin, co-sensitized with a benzotriazole-containing dye (WS-5) in iodine and cobalt redox systems, and high PCEs of 10.21 and 10.42 %, respectively, were obtained. An unprecedented breakthrough was obtained by making one sensitizer suitable for several electrolyte systems because of its appropriate molecular orbitals and co-sensitizer.

Fine-tuning π-spacer for high efficiency performance DSSC: A theoretical exploration with [formula omitted] based organic dye

Based on density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches, a series of triphenylamine based organic dyes that modified by electron-withdrawing (EW) or electron-deficient (ED) substituent groups are investigated. The properties of all the isolated dyes, including frontier molecular orbital, intramolecular charge transfer, absorption spectra, maximal photon generated current (Jph) and intermolecular interaction between dye and I2 are investigated theoretically to confirm which dyes can produce great performance for dye-sensitized solar cell (DSSC). Subsequently, the structures of dye combined with (TiO2)64 cluster are optimized by means of Vienna ab initio simulation package (VASP) code. Then the interfacial interaction between the dye and semiconductor is further discussed to reveal the interfacial charge injection process by means of interfacial electron transfer code. The importance of fine-tuning π-spacer is also demonstrated by the density of state (DOS) plot and photo-induced charge transfer dynamics. Compared with other dyes, TA-CN dye shows outstanding performance because of the strong coupling of the absorbed dye's orbitals with substrate orbitals and the fast as well as complete charge injection process. The purpose of our study is expected to provide a promising way to design possible candidate sensitizers for DSSC.

Highly uniform hierarchical Zn2SnO4 microspheres for the construction of high performance dye-sensitized solar cells

3D hierarchical Zn2SnO4 with different sizes are fabricated via a one-step hydrothermal method. And the DSSCS devices based on Zn2SnO4 microspheres photoanode are designed. The 1.20 μm Zn2SnO4 microspheres show the best power conversion efficiency.

Significant light absorption enhancement by a single heterocyclic unit change in the π-bridge moiety from thieno[3,2-b]benzothiophene to thieno[3,2-b]indole for high performance dye-sensitized and tandem solar cells

Thieno[3,2-b]indole-based organic sensitizers were synthesized to enhance the light absorption ability and exhibited superior performance for dye-sensitized solar cells.

Metal-free branched alkyl tetrathienoacene (TTAR)-based sensitizers for high-performance dye-sensitized solar cells

New branched alkyl tetrathienothiophene (TTAR)-based organic sensitizers with power conversion efficiency up to 11%.

A graphene quantum dot decorated SrRuO3mesoporous film as an efficient counter electrode for high-performance dye-sensitized solar cells

The predominant synergic effect of GQDs and SrRuO3CEs drives faster ion diffusions and electron transfer, thereby contributing to excellent catalytic activity of the SRO–GQD CE towards I3−reduction.

Efficiency enhancement in dye-sensitized solar cells using the shape/size-dependent plasmonic nanocomposite photoanodes incorporating silver nanoplates.

In this work, we describe the efficiency enhancement in dye-sensitized solar cells (DSSCs) by using TiO2/silver nanoplate plasmonic nanocomposite photoanodes. The nanocomposite photoanodes with tunable plasmonic properties assembled from shape/size-selected silver (Ag) nanoplates were applied to enhance the light absorption for high-performance DSSCs. It was found that the localized surface plasmon resonance can be tuned over a range from 500 to 1000 nm, which is strongly dependent on the shape and size of Ag nanoplates and the refractive index of the surrounding dielectric. The effects of the size and shape of Ag nanoplates on the surface plasmonic resonance and the efficiency of DSSCs were evaluated experimentally. Furthermore, a three-dimensional finite element method was employed to investigate the localized surface plasmon resonance (LSPR) for the shape and size effect of Ag nanoplates.

High performance dye-sensitized solar cells based on platinum nanoroses counter electrode

In this study, we controlled the growth of crystalline plane to synthesize the vertical platinum nanopelts onto fluorine doped tin oxide (FTO) glass to construct the platinum nanoroses (PtNRs) by an easy electrochemical deposition (ECD) method at room temperature in the normal atmospheric environment, and applied the PtNRs as a counter electrode (CE) for dye-sensitized solar cell (DSSC). The morphologies and crystalline nanostructures of the ECD PtNRs were examined by field emission scanning electron microscopy and the high-resolution transmission electron microscopy. The electrocatalytic properties of the ECD PtNRs were analyzed by cyclic voltammetry and electrochemical impedance spectrum. The power conversion efficiency (PCE) of the DSSC assembled with the ECD PtNRs CE was examined under the illumination of AM 1.5 (100mWcm−2). The ECD PtNRs showed well contact behavior with FTO surface and offered a large surface area to promote the redox reaction rates therefore increased the exchange current density. Due to the PtNRs showed the macroporous structure, the electrolyte can easily diffuse through the open space between the nanopelts, resulting in improved kinetics for charge-transfer processes and reduced the charge-transfer resistance. Our findings suggest that the catalytic efficiency of PtNRs with a specific crystal plane was significantly greater than that of a traditional Pt film catalyst. In combination with a N719 dye-sensitized TiO2 working electrode and an iodine-based electrolyte, the DSSC assembled with the PtNRs CE achieved a PCE of 6.58%, almost 10% higher than that of a cell prepared with a conventional sputtering Pt film CE (6.00%). These results provide a potential strategy for electrochemical catalytic applications.

Design of high-performance dye-sensitized solar cells by variation of the dihedral angles of dyes

Two new metal-free organic sensitizers (i.e., IAH and IDH) based on a D−π−A configuration were designed to elucidate the effect of the alkyl chain location at the thiophene π-bridge on their photovoltaic performance. IAH, in which the alkyl chain is closer to the acceptor moiety, is more planar than IDH, in which the alkyl chain is closer to the donor moiety. Therefore, IAH induces more effective π-conjugation and electron injection from the dye excited state to the TiO2 conduction band, leading to a higher short-circuit photocurrent (Jsc). In contrast, IDH more effectively inhibits electron transfer from the conduction band of TiO2 to the dye excited state, resulting in a higher open-circuit photovoltage (Voc). Under standard AM 1.5 simulated sunlight, the IAH-based cells exhibited an overall conversion efficiency of 6.90%; this value is higher than that of the IDH-sensitized cells, which reached 86% of the conversion efficiency of N719 cells.

First-Principle Characterization of the Adsorption Configurations of Cyanoacrylic Dyes on TiO2 Film for Dye-Sensitized Solar Cells.

The loading of sensitizers on a semiconductor is crucial for determining the light-harvesting efficiency of dye-sensitized solar cells (DSSCs). The interfacial properties of dyes adsorbed on a TiO2 film, such as adsorption configurations and adsorption energy, can influence the total amount of dye sensitizers that loads and the stability of a DSSC device. Therefore, it is important to characterize the adsorption properties of sensitizers on TiO2 films atomically and electronically to ensure rational structure-based dye design for high-performance DSSCs. Due to the complex properties of interfacial dyes, previous works on the identification of adsorption configurations of dyes on TiO2 have sometimes been controversial, in particular, the essential IR band assignments. In this study, we employed density functional theory to investigate the adsorption energies, geometries, and vibrational frequencies of various adsorption configurations of 2-cyano-3-(thiophen-2-yl)acrylic acid adsorbed on TiO2. We performed a comparative assignment of the calculated vibrational peaks of tridentate and bidentate configurations to the experimental FT-IR spectra simultaneously. Our work backs up the coexistence of tridentate and bidentate bridging configurations, first proposed by Meng and co-workers. Moreover, our comparative IR mode assignments provide clues for further studies of the interfacial properties of dyes adsorbed on TiO2. Study of the transformation mechanisms between tridentate and bidentate modes suggests that the bidentate bridging configuration is a kinetically trapped adsorption mode and the tridentate configuration is thermodynamically the most stable one. Finally, we investigated the photophysical properties of a D-π-A dye in tridentate and bidentate adsorption configurations.

Novel poly(vinylidene fluoride-co-hexafluoro propylene)/polyethylene oxide based gel polymer electrolyte containing fumed silica (SiO2) nanofiller for high performance dye-sensitized solar cell

Novel gel polymer electrolytes (GPEs) are prepared using poly(vinylidene fluoride-co-hexafluoro propylene) copolymer (PVdF-HFP) and polyethylene oxide (PEO) in presence of fumed silica nanofiller with the designated system of PVdF-HFP:PEO:EC:PC:NaI:SiO2:I2. GPEs are examined using electrochemical impedance spectroscopy (EIS) and the highest ionic conductivity of 8.84mScm−1 is achieved after incorporation of 13wt.% of fumed silica (SiO2). Temperature-dependent ionic conductivity study confirms that GPE system follows Arrhenius thermal activated model. GPEs are characterized for structural studies using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. GPEs are used to fabricate dye-sensitized solar cells (DSSCs) and tested under 1 Sun irradiation, obtaining the highest energy conversion efficiency of 9.44% after the incorporation of 13wt.% fumed silica. Cyclic voltammetry has been performed to analyse electrochemical properties of gel polymer electrolytes.

Regulation of Microstructure and Composition of Cobalt Selenide Counter Electrode by Electrochemical Atomic Layer Deposition for High Performance Dye-Sensitized Solar Cells

By means of electrochemical atomic layer deposition (ECALD), cobalt selenide counter electrodes have been successfully prepared on FTO substrate for the first time. The as-grown films presented amorphous structure and their composition and microstructure could be regulated effectively by adjusting the depositing potential of Se via the route of ECALD. Cycle voltammograms and Tafel polarization measurements revealed that the cobalt selenide counter electrode exhibited an excellent catalytic activity and stability in the I−/I3− system. Due to the more active catalytic sites and less charge-transfer resistance, the Co1.2Se counter electrode yielded faster and more complete reduction of I3− to I− than the Pt and other compositions of cobalt selenide. As a result, the dye-sensitized solar cell based on the Co1.2Se counter electrode yielded a photoconversion efficiency of 9.28%, which improved by 136% than that of the DSSC based on the Pt electrode (6.84%). Taking the facility and cost efficiency into consideration, ECALD has great potential in preparing high efficient counter electrode for high performance DSSCs.

Cyclopentadithiophene bridged organic sensitizers with different auxiliary acceptor for high performance dye-sensitized solar cells

A series of triphenylamine-based dye sensitizers were designed by modifying the auxiliary acceptors and their positions for the potential use in dye-sensitized solar cells (DSSCs). The geometrical structures, photoinduced charge transfer character together with optical properties for these dyes adsorbed on (TiO2)6 have been investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. The effects of auxiliary units and their positions on the optoelectronic properties of the dyes are demonstrated. The results illustrate that the dyes with auxiliary acceptors close to the cyanoacrylic acid show very narrow band gap (HOMO-LUMO), leading to an obvious red-shifted absorption band in contrast to the dyes with additional acceptors next to the donor part. Further analyses of the dye-(TiO2)6 systems manifest that there has strong electronic coupling between the dyes and the (TiO2)6 surface. The results are expected to provide a useful reference to the future design and optimization for new highly efficient metal-free organic dyes.