Changneng Zhang

Low molecular mass organogelator based gel electrolyte with effective charge transport property for long-term stable quasi-solid-state dye-sensitized solar cells.

Stable quasi-solid-state dye-sensitized solar cells (DSC) were fabricated using 12-hydroxystearic acid as a low molecular mass organogelator (LMOG) to form gel electrolyte. TEM image of the gel exhibited the self-assembled network constructed by the LMOG, which hindered flow and volatilization of the liquid. The formation of less-mobile polyiodide ions such as I 3 (-) and I 5 (-) confirmed by Raman spectroscopy increased the conductivity of the gel electrolytes by electronic conduction process, which should be rationalized by the Grotthuss-type electron exchange mechanism caused by rather packed polyiodide species in the electrolytes. The results of the accelerated aging tests showed that the gel electrolyte based dye-sensitized solar cell could retain over 97% of its initial photoelectric conversion efficiency value after successive heating at 60 degrees C for 1000 h and device degradation was also negligible after one sun light soaking with UV cutoff filter for 1000 h.

Enhanced photovoltaic performance of dye-sensitized solar cells using a highly crystallized mesoporous TiO2 electrode modified by boron doping

Highly crystallized boron-doped anatase TiO2 nanoparticles are prepared by a facile synthetic route and successfully used as the photoanode of dye-sensitized solar cells (DSCs). We have observed that the boron doping could improve the crystallinity of TiO2. Moreover, the highly crystallized anatase boron-doped TiO2 were analyzed by electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS) and UV-vis spectroscopy, and the internal resistances of the boron-doped DSCs were studied by measuring the electrochemical impedance spectra (EIS). The improved photocurrent density of the boron-doped DSCs is due to a significant enhancement of IPCE in the range 370–650nm in comparison with that of the undoped DSC. Meanwhile, the energy-conversion efficiency of the cell based on the B-doped TiO2 electrode is enhanced significantly, by about 9%, compared to that of the undoped DSC. Overall, DSCs based on B-doped electrodes show good stability and remain over 95% of their initial efficiency under visible light soaking for more than 2400 h.

A New Type of Electrolyte with a Light‐Trapping Scheme for High‐Efficiency Quasi‐Solid‐State Dye‐Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) are attracting both academic and industrial interest owing to their high-effi ciency and potential low-cost. [ 1 ] The electrolyte, containing the I − /I 3 − redox couple, is the one of the most-important components of a DSSC, and directly infl uences their performance and stability. [ 2,3 ] Generally, the role of the electrolyte in a DSSC is to fi nish the charge cycle, including the transport of the I − /I 3 − redox couple, [ 4 ] the regeneration of oxidized dye at the dyed TiO 2 /electrolyte interface and the reduction of I 3 − at the counter electrode. [ 5 ] However, I 3 − in the electrolyte will absorb visible light, [ 6 ] which results in energy loss. Furthermore, due to the inhomogeneous dye distribution, [ 7 ] a certain part of the incident light transmits through the photoanode, which decreases the light-harvesting effi ciency. As we know, although relatively large particles have already been used in DSSCs to help increase the light-harvesting effi ciency, still part of the incident light will transmit through the photoanode. Moreover. an excess of large particles will not only lower the light-harvesting effi ciency over the whole range of visible wavelengths owing to enhanced light refl ection at the conducting glass/TiO 2 interface, but also decrease the electron-transfer yield. [ 8 ] As reported previously, [ 9 ] light trapping has become a standard technique to increase the light absorption of incident light in the active layers of hydrogenated amorphous-siliconbased solar cells, based on the use of textured substrates and highly refl ective back contacts. This triggered our interest in exploring a new type of electrolyte with a light-trapping scheme to enhance the light-harvesting effi ciency of DSSCs. Liquid crystals (LCs), as the fourth state of matter, combining properties of liquids and solids, [ 10 ] are usually used as the medium for organic catalytic synthesis, [ 11 ] functional nanostructured materials, [ 12 ] and especially in the fi eld of polymer-dispersed liquidcrystal (PDLC) displays, due to the light-scattering properties of the LC. [ 13 ] Thus, we tried to introduce an LC to the liquid electrolyte of a DSSC. Furthermore, when the LC was added to the liquid electrolyte, a quasi-solid-state electrolyte was formed, which could help to resolve the sealing diffi culty in the DSSCs.

Superior energy band structure and retarded charge recombination for Anatase N, B codoped nano-crystalline TiO2 anodes in dye-sensitized solar cells

This work reports the preparation of N, B codoped TiO2 (N, B–TiO2) electrodes in dye-sensitized solar cells (DSCs) by a facial modified sol–gel method. After the nitrogen and boron dopants incorporated into the TiO2 electrodes, the cubic-like TiO2 nanocrystallites with diameters of 22∼24 nm were obtained efficiently. The back electron transfer of the DSC based on the N, B–TiO2 electrode was studied by measuring the electrochemistry impedance spectra (EIS) and the EIS for the DSCs showed that the enhanced electron lifetime for the dye-sensitized B, N–TiO2 solar cells could be attributed to the formation of an O–Ti–B–N bond in the TiO2 photoelectrode, which retards electron recombination at the dyed N, B–TiO2 photoelectrode/electrolyte interface after N, B codoping as compared to the undoped DSC. We found that a high efficiency of 8.4% for the DSC (active area:4 cm2) based on the N, B–TiO2 anode under 0.2 sun illumination was received. In particular, the photovoltaic performance of the DSC under high temperature conditions (60 °C) and one-sun light soaking over a time of more than 1100 h showed that the DSC based on the N, B–TiO2 electrode exhibited a better stability compared to the undoped DSC. The excellent photoelectrochemical performance could be attributed to the ideal combination of retarded electron recombination and superior energy band structure from the unique N, B–TiO2 particle structure.

Theoretical modeling of the series resistance effect on dye-sensitized solar cell performance

Based on the continuity equations and the equivalent circuit, the conductivity of substrates and the resistances of silver grid in dye-sensitized solar cell (DSC) are investigated. The complete I-V characteristics of DSC are obtained with different internal resistances. The theoretical and experimental results show internal resistances dominate the fill factor of DSC. At the same time, DSC module is investigated by numerical simulation under parallel connection with different illumination intensities. It can be found the high resistivity of substrates and the high illumination intensity lead to a lower optimal width in the DSC module.

Multiple adsorption of tributyl phosphate molecule at the dyed-TiO2/electrolyte interface to suppress the charge recombination in dye-sensitized solar cell

Electron recombination and dye aggregation at the dyed-TiO2/electrolyte interface are still problems in dye-sensitized solar cell (DSC) research. In this paper, tributyl phosphate (TBpp) as a special additive to modify the dyed-TiO2/electrolyte interface was introduced to enhance the photovoltaic performance. The adsorption mode of TBpp and the interaction between cis-dithiocyanate-N,N′-bis-(4-carboxylate-4-tetrabutylammonium carboxylate-2,2′-bi-pyridine) ruthenium(II) (N719) and TBpp were investigated. It was found that one TBpp parent molecule split into several smaller fragments and formed four anchoring modes on the TiO2 surface. It was very interesting that the molecular cleavage of TBpp and adsorption of N719 assisted each other on the sensitized TiO2 surface. The fragments distributed around N719 result in steric hindrance, consequently hydrogen-bonding among N719 molecules was decreased. The unstable type N719 transformed into stable type N719 accompanied by molecular cleavage of TBpp and the N719 aggregation was reduced. Furthermore, these new fragments were multiply adsorbed on the non-sensitized TiO2 surface to form an insulating barrier layer. Therefore, the electron recombination at the dyed-TiO2/electrolyte interface was restrained. Besides the change of surface configuration, the TiO2 band edge negatively shifted and the rate of electron transport in the TiO2 films decreased with the addition of TBpp. As a result, an increase in the photoelectric conversion efficiency (η) was obtained of almost 40%.

TiO2 Sub-microsphere Film as Scaffold Layer for Efficient Perovskite Solar Cells.

TiO2 sub-microspheres composed of anatase granular-like nanocrystallines with an average diameter ∼250 nm are synthesized using sol-gel method and employed as the scaffold layer for efficient mesocopic perovskite solar cells. Compared with mesoporous TiO2 films composed of ∼18 nm nanoparticles, the sub-microsphere films show superior light-trapping characteristics and significantly improve the light-harvesting capability of the solar cells. In addition, the charge-transport performance is also dramatically improved according to the transient photocurrent decay despite there being no significant difference in the perovskite layer surface morphology. As a result, an average power conversion efficiency of 15% with a highly uniform distribution is achieved for the solar cells with TiO2 sub-microsphere films, 12% higher than those with TiO2 nanoparticle films. The combination of light-harvesting capability and fast charge transfer make the TiO2 sub-microsphere film a good candidate as the scaffold layer for efficient perovskite solar cells.

Ionic liquid crystal-based electrolyte with enhanced charge transport for dye-sensitized solar cells

A room temperature ionic liquid crystal, 1-dodecyl-3-ethylimidazolium iodide (C12EImI), and an ionic liquid, 1-decyl-3-ethylimidazolium iodide (C10EImI), have been synthesized, characterized and employed as the electrolyte for dye-sensitized solar cells (DSSC). The physicochemical properties show that a smectic A (SmA) phase with a lamellar structure is formed in C12EImI. Both C12EImI and C10EImI have good electrochemical and thermal stability facilitating their use in DSSC. The steady-state voltammograms reveal that the diffusion coefficient of I3− in C12EImI is larger than that in C10EImI, which is attributed to the existence of the SmA phase in C12EImI. Because the iodide species are located between the layers of imidazolium cations in C12EImI, exchange reaction-based diffusion is increased with a consequent increase in, the overall diffusion. The electrochemical impedance spectrum reveals that charge recombination at the dyed TiO2/electrolyte interface of a C12EImI-based DSSC is reduced due to the increase in I3− diffusion, resulting in higher open-circuit voltage. Moreover, both short-circuit current density and fill factor of the C12EImI based DSSC increase, as a result of the increasing transport of I3− in C12EImI. Consequently, the photoelectric conversion efficiency of C12EImI-based DSSC is higher than that of the C10EImI-based DSSC.

TiO2 SUB-MICROSPHERES AS A BI-FUNCTIONAL SCATTERING LAYER FOR HIGH-PERFORMANCE DYE-SENSITIZED SOLAR CELLS

The sub-microspheres play multiple roles in enhancing dye adsorption and light-scattering to improve the performance of dye-sensitized solar cells (DSSCs). In this work, the well-defined TiO2 sub-microspheres with anatase granular-like nanocrystals are prepared in high yield by combining hydrolytic process with solvothermal treatment. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results indicated that plenty of rhombic nanoparticles with ~ 18 nm diameter having mutual contacts to neighboring nanoparticles were densely self-assembled into sub-microspheres, and abundant mesopores existed in the whole sub-microspheres with superior light scattering ability. The appropriate pore diameter and relatively high specific surface area of the as-obtained sub-microsphere result in a higher dye adsorption. As expected, by using the sub-microspheres as a scattering layer, a higher photovoltaic conversion efficiency of 10.15% is obtained for DSSCs.

Gel electrolyte materials formed from a series of novel low molecular mass organogelators for stable quasi-solid-state dye-sensitized solar cells

Electrolyte materials are the key components in dye-sensitized solar cells (DSCs) and are very crucial to the performance and long-term stability of DSCs. We developed a series of diamide derivatives as novel low molecular mass organogelators (LMOGs) for DSCs. These LMOGs contain different numbers (2, 6, 5 and 9) of methylene groups (–CH2–) between the two amide carbonyl groups and exhibit distinctive self-assembly behaviors. The gel electrolytes prepared by these LMOGs possess high gel-to-solution transition temperatures (over 100 °C) and the stability of DSCs is largely enhanced. More importantly, the parity of the number of –CH2– and their special molecular arrangements have a remarkable influence on the self-assembly of the gelators resulting in a significantly different morphology, and further influence the photovoltaic performances of DSCs. It is found that the LMOGs containing odd-numbered –CH2– lead to a much better charge transport of the gel electrolytes, inducing a longer electron lifetime and higher incident photon-to-electron conversion efficiency compared with the LMOGs containing even-numbered –CH2–. Finally, a superior quasi-solid-state DSC based on the gelator containing five –CH2– is obtained, which exhibits a photoelectric conversion efficiency of 7.53% and excellent thermal and light-soaking stabilities during accelerated aging tests.