Hongshan He

8-Hydroxylquinoline as a strong alternative anchoring group for porphyrin-sensitized solar cells.

8-Hydroxylquinoline (OQ) is demonstrated for the first time as a strong alternative anchoring group porphyrin dyes to improve the long-term stability of solar cells.

Cobalt ferrite nanoparticles: Achieving the superparamagnetic limit by chemical reduction

An unanticipated superparamagnetic response has been observed in cobalt ferrite materials after thermal treatment under inert atmosphere. Cobalt ferrite particles were prepared via normal micelle precipitation that typically yields CoxFe3−xO4 nanoparticles (x=0.6−1.0). While samples thermally treated under oxygen show majority spinel phase formation, annealing in nitrogen gas yields materials consisting of Co-Fe alloy, FeS, and CoFe2O4 spinel. After thermal treatment, thermomagnetic studies reveal composition-insensitive, but highly treatment-sensitive, saturation magnetization, coercivity, blocking temperature, and Verwey transition temperature dependence. Extremely high saturation magnetization (159 emu/g) with low coercivity (31 Oe) was observed for one of the treated compositions, which drastically deviates from prototypical cobalt ferrite with large magnetocrystalline anisotropy. We attribute such unique magnetic response to Co-Fe alloy coexisting with FeS and CoFe2O4 spinel where the diameter of the...

Fine tuning of fluorene-based dye structures for high-efficiency p-type dye-sensitized solar cells.

We report on an experimental study of three organic push-pull dyes (coded as zzx-op1, zzx-op1-2, and zzx-op1-3) featuring one, two, and three fluorene units as spacers between donors and acceptors for p-type dye-sensitized solar cells (p-DSSC). The results show increasing the number of spacer units leads to obvious increases of the absorption intensity between 300 nm and 420 nm, a subtle increase in hole driving force, and almost the same hole injection rate from dyes to NiO nanoparticles. Under optimized conditions, the zzx-op1-2 dye with two fluorene spacer units outperforms other two dyes in p-DSSC. It exhibits an unprecedented photocurrent density of 7.57 mA cm(-2) under full sun illumination (simulated AM 1.5G light illumination, 100 mW cm(-2)) when the I(-)/I3(-) redox couple and commercial NiO nanoparticles were used as an electrolyte and a semiconductor, respectively. The cells exhibited excellent long-term stability. Theoretical calculations, impedance spectroscopy, and transient photovoltage decay measurements reveal that the zzx-op1-2 exhibits lower photocurrent losses, longer hole lifetime, and higher photogenerated hole density than zzx-op1 and zzx-op1-3. A dye packing model was proposed to reveal the impact of dye aggregation on the overall photovoltaic performance. Our results suggest that the structural engineering of organic dyes is important to enhance the photovoltaic performance of p-DSSC.

NiO nanosheets as efficient top hole transporters for carbon counter electrode based perovskite solar cells

Herein, we present fully printable carbon electrode based perovskite solar cells using highly crystalline NiO nanosheets as top hole transport layers, mesoporous TiO2 nanoparticles as a bottom electron transport layer and ZrO2 as an intermediate spacer layer, respectively. Time-resolved photoluminescence decay measurements, electron impedance spectroscopy and transient photovoltage decay measurements have revealed that the NiO nanosheets as top hole transporters exhibit superior charge collection efficiency and a prolonged charge lifetime. As a result, an impressive power conversion efficiency of 14.2% is achieved under standard testing conditions.

Modulated Charge Injection in p-Type Dye-Sensitized Solar Cells Using Fluorene-Based Light Absorbers

In this study, new pull-push arylamine-fluorene based organic dyes zzx-op1, zzx-op2, and zzx-op3 have been designed and synthesized for p-type dye-sensitized solar cells (p-DSCs). In zzx-op1, a di(p-carboxyphenyl)amine (DCPA) was used as an electron donor, a perylenemonoimide (PMID) as an electron acceptor, and a fluorene (FLU) unit with two aliphatic hexyl chains as a π-conjugated linker. In zzx-op2 and zzx-op3, a 3,4-ethylenedioxythiophene (EDOT) and a thiophene were inserted consecutively between PMID and FLU to tune the energy levels of the frontier molecular orbitals of the dyes. The structural modification broadened the spectral coverage from an onset of 700 nm for zzx-op1 to 750 nm for zzx-op3. The electron-rich EDOT and thiophene lifted up the HOMO (highest occupied molecular orbital) levels of zzx-op2 and zzx-op3, making their potential more negative than zzx-op1. When three dyes were employed in p-type DSCs with I(-)/I3(-) as a redox couple and NiO nanoparticles as hole materials, zzx-op1 exhibited impressive energy conversion efficiency of 0.184% with the open-circuit voltage (VOC) of 112 mV and the short-circuit current density (JSC) of 4.36 mA cm(-2) under AM 1.5G condition. Density functional theory calculations, transient photovoltage decay measurements, and electrochemical impedance spectroscopic studies revealed that zzx-op1 sensitized solar cell exhibited much higher charge injection efficiency (90.3%) than zzx-op2 (53.9%) and zzx-op3 (39.0%), indicating a trade-off between spectral broadening and electron injection driving force in p-type DSCs.

TiO2 nanotube membranes on transparent conducting glass for high efficiency dye-sensitized solar cells

Crack-free TiO(2) nanotube (NT) membranes were obtained by short time re-anodization of a sintered TiO(2) NT array on Ti foil, followed by dilute HF etching at room temperature. The resulting freestanding TiO(2) membranes were opaque with a slight yellow color having one end open and another end closed. The membranes were then fixed on transparent fluorine-tin-oxide glass using a thin layer of screen-printed TiO(2) nanoparticles (NPs) as a binding medium. It was found that low temperature treatment of the resulting NT/NP film under appropriate pressure before sintering at 450 °C was critical for successful fixation of the NT membrane on the NP layer. The resulting films with open-ends of NT membranes facing the NP layer (open-ends down, OED, configuration) exhibited better interfacial contact between NTs and NPs than those with closed-ends facing the NP layer (closed-ends down, CED, configuration). The cells with an OED configuration exhibit higher external quantum efficiency, greater charge transfer resistance from FTO/TiO(2) to electrolyte, and better dye loading compared to CED configurations. The solar cells with the OED configuration gave 6.1% energy conversion efficiency under AM1.5G condition when the commercial N719 was used as a dye and I(-)/I(3)(-) as a redox couple, showing the promise of this method for high efficiency solar cells.

Synthesis, Characterization, and Near-Infrared Photoluminescence of Novel Neodymium(III) Complexes

A series of monoporphyrinate neodymium(iii) complexes stabilized by the anionic tripodal ligand hydridotris(pyrazol-1-yl)borate were prepared and characterized. These complexes were characterized by elemental analysis and spectroscopy. The structure of resulting complex was determined by single-crystal X-ray diffraction. The complex crystallized in the monoclinic space group P21/c, with a 13.7347(11), b 27.156(2), c 15.5397(13) A, β 114.1490(10)°, and V 5288.8(7) A3. The neodymium(iii) ion is coordinated by four nitrogen atoms from the porphyrinate dianion and three nitrogen atoms from the anionic tripodal ligand. Photoluminescence studies showed that the porphyrinate dianion absorbed light and transferred energy to the Nd3+ centre, a process which then allowed the metal ion to emit efficiently at 885, 900, and 1071 nm. The effects of the substituent and the solvent on emission efficiency were also investigated.

Porphyrin dyes on TiO2 surfaces with different orientations: a photophysical, photovoltaic, and theoretical investigation.

Porphyrin dyes with a triphenylamino group as an electron donor, para- or meta-benzoic acids as electron acceptors, and hydrogen (H) or mesityl (M) substituents on the meso position as auxiliary groups were synthesized. Their photophysical properties and photovoltaic performance in dye-sensitized solar cells were investigated. All four porphyrins exhibited similar photophysical properties in the solution and dye-loading densities on the surface of TiO2 nanoparticles; however, the p-benzoic acid functionalized porphyrins, p-H(M)PZn, gave better photovoltaic performance than m-benzoic acid functionalized porphyrins, m-H(M)PZn. Theoretical calculations indicated that the electron density on the frontier molecular orbital was more delocalized to p-benzoic acid than to m-benzoic acid. Absorption spectra indicated the stronger H-aggregation in m-H(M)PZn than that in p-H(M)PZn on the surface of TiO2 nanoparticles. The mesityl groups in the meso positions reduced the dye-loading density due to steric hindrance between dyes. As a result, the p-MPZn exhibited the best energy conversion efficiency among the four porphyrins studied. This efficiency was further enhanced when a complementary dye BET was used.

8-Hydroxylquinoline-conjugated porphyrins as broadband light absorbers for dye-sensitized solar cells

Three porphyrin dyes, DPZn-HOQ, PZn-HOQ and DPZn-COOH, were synthesized and characterized for dye-sensitized solar cells. Both DPZn-HOQ and DPZn-COOH exhibited a donor–π–acceptor configuration with N,N-dimethylaniline as a donor and 8-hydroxylquinoline (HOQ) and para-benzoic acid (BZA) as acceptors, respectively. PZn-HOQ is an analogue of DPZn-HOQ without a donor. It was found that DPZn-HOQ exhibited broader and stronger light absorption capability in the red region than DPZn-COOH. Theoretical calculations showed that the electrons were delocalized to the 8-hydroxylquinoline ring in DPZN-HOQ. The DPZn-HOQ-sensitized solar cells exhibited higher energy conversion efficiency (3.09%) than DPZn-COOH-sensitized solar cells (1.76%) under the same conditions. The results were consistent with the incident photon to current conversion efficiency (IPCE) spectra. The electrochemical impedance spectroscopy studies revealed that HOQ-conjugated porphyrin exhibited high electron recombination resistance and a long electron lifetime, which was attributed to the effective shielding of DPZn-HOQ from the electrolyte due to its tilted orientation on the surface of TiO2 nanoparticles. The efficiency of DPZn-HOQ-sensitized solar cells was further increased to 3.41% when a complementary dye BET was used.

Synthesis, characterization and near-infrared photoluminescent studies of diethyl malonate appended mono-porphyrinate lanthanide complexes

A new unsymmetrical diethyl malonate appended porphyrin and its Yb3+, Er3+ and Nd3+ complexes were prepared and characterized by elemental analysis, NMR, IR, UV-visible and mass spectral methods. The results revealed that the porphyrinate behaved as a tri-deprotonated hexadentate ligand with the appended diethyl malonate group coordinated to the lanthanide ion as an anion. Photoluminescent studies showed that the porphyrin ring transferred the absorbed visible light to the metal ions, which led to emission characteristic of the lanthanide ions in the near-infrared region. The factors affecting the emission intensity were also investigated.