Miaoyu Li

High performance of Pt-free dye-sensitized solar cells based on two-step electropolymerized polyaniline counter electrodes

A two-step cyclic voltammetry (CV) approach is employed in a quick and controllable electropolymerization of polyaniline (PANI) nanofibers with a short-branched structure onto fluorinated tin oxide (FTO) glass substrates as counter electrodes (CEs) for Pt-free dye-sensitized solar cells (DSSCs). In the two-step CV method, a small quantity of PANI as a function of the crystal nucleus in the crystal growth, is pre-electropolymerized under a suitably high potential for one cycle at the first-step, then subjected to the second-step for PANI electropolymerization at a low potential for a small number of scans. The well-controlled PANI nanofibers with high performance can be electropolymerized quickly using the two-step mode. The extensive CVs demonstrate the two-step PANI CE has superior electrocatalytic activity for the I3− reduction. Moreover, electrochemical impedance spectroscopy shows that the two-step PANI CE has a lower series resistance and charge-transfer resistance than the PANI CE prepared by conventional one-step CV electropolymerization. Therefore, the DSSC assembled with the two-step PANI CE exhibits an enhanced photovoltaic conversion efficiency of 6.21% (compared to 5.01% for the DSSC with the one-step PANI CE), up to ∼97% of the level of the DSSC using Pt CE. As the result, the two-step CV electropolymerized PANI CE can be considered as a promising alternative CE for Pt-free DSSCs.

Electrospun lead-doped titanium dioxide nanofibers and the in situ preparation of perovskite-sensitized photoanodes for use in high performance perovskite solar cells

Lead-doped TiO2 nanofibers (TNFs) are fabricated by using an electrospun method, followed by the in situ preparation of perovskite-sensitized photoanode for use in perovskite solar cells (PSC). The electrospun TNFs can provide direct pathways for the rapid collection and transmission of photogenerated electrons. The photoanode based on the in situ method shows not only excellent contacting between the TNF and perovskite, but also abundant perovskite filling in it. These can be conducive not only to the separation and transmission of the electron and hole, but also to the absorption and utilization of sunlight. Finally, a high performance PSC with the cell efficiency of 9.03% is obtained without any hole transporting materials.

Preparation of high performance perovskite-sensitized nanoporous titanium dioxide photoanodes by in situ method for use in perovskite solar cells

Perovskite-sensitized nanoporous TiO2 photoanode of several micrometers thickness was prepared for the first time by an in situ technique. The excellent contact between the TiO2 and perovskite could be beneficial to the separation and transmission of the electron and hole while the sufficient filling and abundant CH3NH3PbI3 could enhance the absorption and utilization of sunlight to finally obtain an efficient perovskite solar cell. Note that 10.03% of cell efficiency was achieved without adding hole transporting material into the device.

Co-electrodeposition of MnO2/graphene oxide coating on carbon paper from phosphate buffer and the capacitive properties

MnO2/graphene oxide sheet composite (MnO2/GOS) has been co-electrodeposited on the thermally treated carbon paper (TTCP) in phosphate buffer solution containing GOS and KMnO4. The resulted samples have been characterized by scanning and transmission electron microscopy, Raman, X-ray diffraction, and X-ray photoelectron energy spectroscopy. The results show that the synthesized MnO2 may be δ-MnO2 and the morphology of MnO2/GOS is very different from that of MnO2, indicating that the introduction of GOS in electrolyte can influence the morphology during the deposition. The capacitive properties of the samples are investigated by using cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The specific capacitance of MnO2 for MnO2/GOS can reach about 829xa0Fxa0g−1 at discharged current density of 1.0xa0Axa0g−1 in 1xa0M Na2SO4 aqueous solution, which is larger than that of MnO2 deposited on TTCP. The composite of MnO2/GOS also exhibits excellent cyclic stability with a decrease of 18.5xa0% specific capacitance after 1,500xa0cycles.

Honeycomb-like polypyrrole/multi-wall carbon nanotube films as an effective counter electrode in bifacial dye-sensitized solar cells

AbstractHoneycomb-like polypyrrole/multi-wall carbon nanotube (PPy/MWCNT) film demonstrates as an efficient and semitransparent counter electrode (CE) in bifacial dye-sensitized solar cell (DSSC), which is first fabricated on fluorine-doped tin oxide glass by a facile method using a sacrificial template of poly(methyl methacrylate) (PMMA). The results from ultraviolet–visible spectrophotometer and cyclic voltammetry measurements testify that the honeycomb-like PPy/MWCNT film possesses high transparency for the backside illumination and wonderful electrocatalytic activity for the reduction of triiodide (I3−) to iodide (I−) in the bifacial DSSC. Electrochemical impedance spectroscopy results indicate that the honeycomb-like nanostructure combining with the MWCNT decreases the resistance of the PPy/MWCNT film for the transfer of electrons from the external circuit back to the redox electrolyte. The bifacial DSSC based on the honeycomb-like PPy/MWCNT CE achieves 7.07 and 4.11% of the front and rear efficiencies, respectively, which are higher than those of the bifacial DSSC based on the flat PPy CE (5.78 and 3.07%, respectively).n

Fabricating reduced graphene oxide films with high volumetric capacitive performances via thermal and acid treatment

AbstractnConsidering the growing requirement for high-performance energy storage devices, active electrode materials with high volumetric performance are urgently needed, but only few reports devote to the preparation of reduced graphene oxide (rGO) with high gravimetric specific capacitance (Cg) and volumetric specific capacitance (Cv). Here, the thermally treated dense rGO films are further treated with concentrated sulfuric acid to achieve the high Cg, Cv and cycling stability. The optimal film possesses high density of about 2.04xa0gxa0cm−3 and exhibits the maximal Cg and Cv of about 242.3 F g−1 and 494.3 F cm−3 in 1.0xa0mol L−1 H2SO4 electrolyte based on the two-electrode testing system. Furthermore, the optimal film shows excellent cycling stability in 1.0xa0mol L−1 H2SO4 (90.2% capacitance retention after 10000 cycles) and excellent rate capability. It is believed that this strategy can be developed as an effective process to prepare rGO-based materials with high capacitive performance for compact energy storage device.

Moiety effect on the luminescent property of star-shaped triphenylamine (TPA) derivatives as mechanochromic materials

Two TPA-based star-shaped mechanochromic materials, namely ester-TPA and COOH-TPA, were designed and synthesized using TPA as the core and benzoic acid and methyl benzoate as the arms, and then importantly the moiety effect on the luminescent property of the materials was investigated. They displayed similar solvatochromic effects in different solvents for the D–π–A motif with charge transfer from TPA to the benzoic acid or methyl benzoate moiety, which was confirmed by the consistent UV-vis absorption and large differences displayed when dropped into different solvents as well as by orbital distribution analysis using density functional theory. However, they showed different mechanochromism performances, which were investigated by analysing the fluorescent spectrum, fluorescent quantum yield and fluorescence lifetime. The COOH-based emitter showed a better performance with a relatively obvious red-shift for CIE (0.17, 0.35) to (0.26, 0.49) together with transformation from crystalline to amorphous states, indicating the molecular packing pattern had been destroyed, which could be speculated from single-crystal structure analysis and powder X-ray diffraction analysis. In addition, COOH-TPA could also respond to alkalis, leading to a blue-shift and band broadening of the spectra, which might be ascribed to a reduced charge transfer from TPA to benzoic acid owing to deprotonation.