In this study, we demonstrated the synthesis of vanadium sulfide (VS2) via an in situ hydrothermal route, which was subsequently employed as a counter electrode (CE) for Pt-free dye-sensitized solar cells (DSSCs) for the first time. It was demonstrated from scanning electron microscopy that the size of VS2 increased with the increasing temperature, and the morphology was also affected by temperature. Extensive electrochemical performance analysis, including cyclic voltammetry, electrochemical impedance, and Tafel polarization, revealed that the VS2 CE possesses a high electrocatalytic activity for the reduction of triiodide to iodide and a low charge-transfer resistance at the electrolyte/CE interface. The DSSC based on the VS2 CE exhibited a conversion efficiency of 6.24% under an illumination of 100 mW cm−2 as compared to the DSSC based on the Pt CE.

•Quasi-solid-state flexible DSSCs.•The CoS/Ag/Ti electrode showed high catalytic ability as well as Pt electrode.•The novel gel electrolytes displayed significant improvement in electrochemical and photoelectrochemistry capability.•The flexible DSSC with novel gel electrolytes showed significantly enhanced photovoltaic performance.A series dual function of quasi-solid-state gel electrolytes with high conductivity and good catalytic ability were prepared by integrating the carbon nanotubes (CNTs) and conducting polymers including polypyrrole (PPy), polyaniline (PANI) and poly (3,4-ethylenedioxythiophene) (PEDOT) into poly (acrylic acid) (PAA) gel, showing significant improvement in electrochemical and photoelectrochemistry capability used in dye-sensitized solar cells (DSSCs). These novel electrolytes provide three dimensional network structures for transporting electrons, giving a similar conduction mechanism to that of I−/I3− liquid electrolyte system. The electrochemical performance of the CoS/Ag/Ti counter electrode (CE) was evaluated by electrochemical impedance spectroscopy, which revealed that the CoS/Ag/Ti CE exhibited excellent electrocatalytic ability for these novel electrolytes as well as that of in I−/I3− liquid system. The quasi-solid-state flexible DSSC fabricated with the CoS/Ag/Ti CE and novel gel electrolytes integrated PPy, PANI and PEDOT achieved enhanced power conversion efficiency of 6.89%, 7.01% and 7.20% under the irradiation of 100 mW cm−2, which have much approached that of the DSSC (7.35%) based on Pt electrode and I−/I3− liquid electrolyte.Download high-res image (212KB)Download full-size image

•The CNTs/VS2 composite were first time prepared and served as counter electrode (CE) for Pt-free DSSC.•The CNTs/VS2 CE showed perfect electrocatalytic ability for I–/I3– electrolyte.•The power conversion efficiency of the DSSC reached 8.02% based on the CNTs/VS2 CE.A hybrid counter electrode (CE) of vanadium sulfide decorated with carbon nanotubes (CNTs/VS2) for efficient dye-sensitized solar cells (DSSCs) was prepared by using an in situ hydrothermal route, and the DSSC based on the CNTs/VS2 CE prepared at 180 °C and contained 0.05 g CNTs exhibits a power conversion efficiency of 7.72% under illumination of 100 mW cm−2. The surface morphology of the VS2 and CNTs/VS2 changed from nanoparticles to one-dimensional (1D) structure was significantly affected by temperature. The electrochemical performance analyses including cyclic voltammetry, electrochemical impedance and Tafel curves for the CNTs/VS2 CEs with different temperatures and CNT contents reveal that the CNTs/VS2 CE possesses the better electrocatalytic activity and lower charge transfer resistance at the electrolyte|CE interface for I−/I3− liquid electrolyte at 180 °C and 0.05 g CNTs.Much higher photovoltaic performance of dye-sensitized solar cell with CNTs/VS2 counter electrode as well as that of Pt configuration device.Download high-res image (171KB)Download full-size image

•Pt-free dye-sensitized solar cells.•The CMTS/CNTs electrode showed excellent catalytic activity as well as Pt.•The enhanced catalytic activity was attributed to synergistic effect of CMTS and CNTs.•The DSSC with the CMTS/CNTs electrode showed a 8.97% photovoltaic performance.An effieient hybrid counter electrode (CE) of CuMnSnS4 (CMTS)/carbon nanotubes (CMTS/CNTs) was prepared by using an in situ solvothermal route, and the dye-sensitized solar cells (DSSCs) based on the CMTS/CNTs CE contained 0.05 g CNTs exhibited an improved power conversion efficiency of 8.97% under illumination of 100 mW·cm−2. The crystal structure, elemental composition and morphology of samples were characterised by using XRD, EDS, TEM and SEM, and we found that the CMTS nanoflowers have no changing with and without polyvinylpyrrolidone particioation except the larger particle size for the latter. The CNTs distributed uniformly in the CMTS nanoflowers and formed a new microsphere. The extensive electrichemical characterizations including cyclic voltammetry, electrochemical impedance and Tafel curves for the CMTS/CNTs were implemented, and it showed better electrocatalytic activity and lower charge transfer resistance at the electrolyte|CE interface for I−/I3− liquid electrolyte compared to the Pt electrode under the optimized condition.Download high-res image (263KB)Download full-size image

Graphene/nickel cobalt oxide (Gr/NiCo2O4) hybrids with a nanostructure were prepared by the use of an in situ hydrothermal route, and applied as a counter electrode (CE) with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) assisted preparation (here abbreviated as P-A) in dye-sensitized solar cells (DSSCs) for the first time. The surface morphology of the bilayer TiO2 photoanode was confirmed using scanning electron microscopy. The superior structural characteristics of the photoanode were advantageous to fast mass transport for the electrolyte, increasing the contact area between the electrolyte and active materials, and enabling the (P-A) Gr/NiCo2O4 CE to speed up the reduction of triiodide to iodide. Also, the CE with a superior nanostructure was evaluated by electrochemical characterization, which indicated that the (P-A) Gr/NiCo2O4 CE possessed excellent electrocatalytic activity in the iodide/triiodide electrolyte and a lower charge transfer resistance of 3.04 ± 0.02 Ω cm2 compared to that of the Pt electrode (3.63 ± 0.02 Ω cm2). Under optimum conditions, the DSSC based on the (P-A) Gr/NiCo2O4 CE achieved a remarkable power conversion efficiency of 8.10%, which is about 8.7% higher than that of the Pt-based DSSC (7.45%). The (P-A) Gr/NiCo2O4 CE can be considered as a promising alternative CE for Pt-free DSSCs.

Nickel sulfide decorated polyaniline (NiS/PANI) co-deposition onto fluorine-doped tin oxide (FTO) substrate using an in situ electropolymerization route and served as the counter electrode (CE) for polysulfide electrolyte in cadmium selenide (CdSe) quantum dots sensitized solar cells (QDSSCs). The NiS/PANI CE provided great electrocatalytic activity and lower charge-transfer resistance compared to the platinum (Pt), NiS and PANI CEs under the same preparation conditions prepared using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization plots characterization. It was because the photoanode was modified with a TiO2 dense layer and thioglycolic acid that the QDSSC exhibited an improved fill factor and short-circuit current density. Under optimum conditions, the QDSSC featuring a NiS/PANI counter electrode provided an enhanced power conversion efficiency of 4.15% under an illumination of 100 mW cm−2.

•The (G-P-A) MoS2/SWCNTs composite were first time prepared and employed as counter electrode (CE) in Pt-free DSSC;.•The (G-P-A) MoS2/SWCNTs CE showed the low Rct of 1.46 Ω·cm2;.•The photo-electric conversion efficiency of the DSSC reached 8.14% based on the (G-P-A) MoS2/SWCNTs CE.A flower-like structure complexes of molybdenum disulfide/single-wall carbon nanotubes (MoS2/SWCNTs) are for the first time synthesized with glucose and poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS) assisted (G-P-A) by the use of an in situ hydrothermal route, and proposed as counter electrode (CE) catalyst for Pt-free dye-sensitized solar cells (DSSCs). The DSSC assembled with the (G-P-A) MoS2/SWCNTs CE exhibits a high photo-electric conversion efficiency of 8.14% under the illumination of 100 mW·cm−2, comparable to that of the DSSC Pt-based (7.78%). Furthermore, the surface morphology of the (G-P-A) MoS2/SWCNTs complexes with flower-like structure is confirmed by using the scanning and transmission electron microscopes (SEM). The superior structural characteristic along with 3D large interconnected interstitial volume is advantageous fast mass transport for the electrolyte, and enables the (G-P-A) MoS2/SWCNTs CE to speed up the reduction of triiodide to iodide. The electrochemical performance of the sample is analyzed from cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It indicates that the (G-P-A) MoS2/SWCNTs CE possesses excellent electrocatalytic activity in iodide/triiodide electrolyte and lower charge transfer resistance of 1.46 Ω·cm2 compared to the Pt electrode (2.44 Ω·cm2). Sum up, the (G-P-A) MoS2/SWCNTs CE can be considered as a promising alternative CE for Pt-free DSSCs.Much higher photovoltaic performance of dye-sensitized solar cell with (G-P-A) MoS2/SWCNTs counter electrode than that of Pt configuration device.

•The NiS/PANI/Ti composite were first time prepared and employed as counter electrode (CE) for Pt-free flexible DSSC.•The NiS/PANI/Ti CE showed great electrocatalytic ability and low resistance of 1.48 ± 0.02 Ω · cm2 for I–/I3–electrolyte.•The power conversion efficiency of the FDSSC reached 7.35% based on the NiS/PANI/Ti CE.A novel titanium foil substrate strategy for the synthesis of high electrocatalytic activity nickel sulfide/polyaniline/titanium (NiS/PANI/Ti) composite film with one-dimensional (1D) net-work structure by using an in situ electropolymerization route, and proposed as platinum (Pt)-free counter electrode (CE) catalyst for flexible dye-sensitized solar cells (FDSSCs). The photovoltaic performance of the FDSSC based on the NiS/PANI/Ti CE exhibits Jsc of 14.56 mA · cm−2, Voc of 0.743 V, FF of 0.68, and corresponding to the η of 7.35%, much higher photoelectric conversion efficiency than that of Pt/Ti CE (6.24%). The NiS/PANI/Ti CE with 1D net-work structure is characterized by using the scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization plots. The NiS/PANI/Ti CE presents multiple functions, i.e., excellent conductivity, great electrocatalytic ability for iodine/triiodine, and lower charge transfer resistance of 1.48 ± 0.02 Ω · cm2 compared to the Pt/Ti electrode (2.25 ± 0.02 Ω · cm2). The photocurrent-photovoltage (J-V) character curves are further used to calculate theoretical short-current densities and open-circuit voltage of the devices. Therefore, the NiS/PANI/Ti CE with 1D net-work structure can be considered as a promising and efficient CE for FDSSCs.Much higher photovoltaic performance of flexible dye-sensitized solar cell with NiS/PANI/Ti counter electrode as well as that of Pt configuration device.

•Pt-free dye-sensitized solar cells.•The nanographite/PPy composite film showed high catalytic activity as well as Pt electrode.•The enhanced catalytic activity was attributed to increased active sites.•The DSSC based on the nanographite/PPy electrode showed a high photovoltaic performance.Nanographite/polypyrrole (NG/PPy) composite film was successfully prepared via in situ polymerization on rigid fluorine-doped tin oxide substrate and served as counter electrode (CE) for dye-sensitized solar cells (DSSCs). The surface morphology and composition of the composite film were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectra and Fourier transform infrared spectroscopy (FTIR). The electrochemical performance of the NG/PPy electrode was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results of CV and EIS revealed that the NG/PPy electrode possessed excellent electrocatalytic activity for the reduction reaction of triiodide to iodide and low charge transfer resistance at the interface between electrolyte and CE, respectively. The DSSC assembled with the novel NG/PPy CE exhibited an enhanced power conversion efficiency of 7.40% under full sunlight illumination as comparing to that of the DSSC based on sputtered-Pt electrode. Thus, the NG/PPy CE could be premeditated as a promising alternative CE for low-cost and high- efficient DSSCs.Much higher photovoltaic performance of dye-sensitized solar cell with nanographite/PPy counter electrode as well as that of Pt configuration device.