Xiaqin Fang

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.

Efficient panchromatic inorganic–organic heterojunction solar cells with consecutive charge transport tunnels in hole transport material

A simple solution-processing method was employed to fabricate panchromatic mp-TiO2/CH3NH3PbI3/P3HT-MWNT/Au solar cells. MWNTs in a P3HT-MWNT composite acted as efficient nanostructured charge transport tunnels and induce crystallization of P3HT, hence significantly enhancing the conductivity of the composite. The fill factor of the hybrid solar cells was greatly enhanced by 26.7%.

New 2,6-modified BODIPY sensitizers for dye-sensitized solar cells

Abstract A series of new metal-free organic dyes with either a boron dipyrromethene (BODIPY)-phenylene or -thiophene as a π-conjugated bridge have been synthesized for application in dye-sensitized solar cells. The photophysical and electrochemical properties of these dyes were investigated and their performance as sensitizers in dye-sensitized solar cells has been measured. The structure–property relationship shows that the introduction of a methoxy group as the donor and a BODIPY-thiophene unit as the π-conjugated bridge are favorable to improve the efficiency of DSSCs. A combination of a methoxy modified donor and BODIPY-thiophene bridge possesses a stronger electron-donating ability and longer wavelength absorption band, and as a sensitizer reveals the best properties of DSSCs, whose conversion efficiency was 2.26%.

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.

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%.

Fourier transform infrared spectroscopy approach for measurements of photoluminescence and electroluminescence in mid-infrared

An improved Fourier transform infrared spectroscopy approach adapting to photoluminescence and electroluminescence measurements in mid-infrared has been developed, in which diode-pumped solid-state excitation lasers were adopted for photoluminescence excitation. In this approach, three different Fourier transform infrared modes of rapid scan, double modulation, and step scan were software switchable without changing the hardware or connections. The advantages and limitations of each mode were analyzed in detail. Using this approach a group of III-V and II-VI samples from near-infrared extending to mid-infrared with photoluminescence intensities in a wider range have been characterized at room temperature to demonstrate the validity and overall performances of the system. The weaker electroluminescence of quantum cascade lasers in mid-infrared band was also surveyed at different resolutions. Results show that for samples with relatively strong photoluminescence or electroluminescence out off the background, rapid scan mode is the most preferable. For weaker photoluminescence or electroluminescence overlapped with background, double modulation is the most effective mode. To get a better signal noise ratio when weaker photoluminescence or electroluminescence signal has been observed in double modulation mode, switching to step scan mode should be an advisable option despite the long data acquiring time and limited resolution.

Insight into the effects of modifying chromophores on the performance of quinoline-based dye-sensitized solar cells

A series of organic dyes based on quinoline as an electron-deficient π-linker, were designed and synthesized for dye sensitized solar cells (DSSC) application. These push-pull conjugated dyes, sharing same anchoring group with distinctive electron-rich donating groups such as N,N-diethyl (DEA-Q), 3,6-dimethoxy carbazole (CBZ-Q), bis(4-butoxyphenyl)amine (BPA-Q), were synthesized by Riley oxidation of CH3 followed by Knoevenagel condensation of the corresponding aldehyde precursors 2a-c with cyanoacrylic acid. The optical, electrochemical, theoretical calculation and photovoltaic properties with these three dyes were systematically investigated. Compared to DEA-Q and CBZ-Q, BPA-Q possesses better light harvesting properties with regard to extended conjugate length, red-shifted intramolecular charge transfer band absorption and broaden light-responsive IPCE spectrum, resulting in a greater short circuit photocurrent density output. BPA-Q also has improved open-circuit voltage due to the apparent large charge recombination resistance. Consequently, assembled with iodine redox electrolytes, the device with BPA-Q achieved the best overall conversion efficiency value of 3.07% among three dyes under AM 1.5G standard conditions. This present investigation demonstrates the importance of various N-substituent chromophores in the prevalent D-π-A type organic sensitizers for tuning the photovoltaic performance of their DSSCs.