Enhanced surface hydroxylation of nanocrystalline anatase films improves photocurrent output and electron lifetime in dye sensitized solar cell photoanodes

Tunable Composition Aqueous-Synthesized Mixed-Phase TiO2 Nanocrystals for Photo-Assisted Water Decontamination: Comparison of Anatase, Brookite and Rutile Photocatalysts

Mixed-phase nanoTiO2 materials attract a lot of attention as advanced photocatalysts for water decontamination due to their intrinsic structure that allows better photo-excited e−cb-h+vb charge separation, hence improved photocatalytic efficiency. Currently, the best-known mixed-phase TiO2 photocatalyst is P25 with approximate composition 80% Anatase/20% Rutile (A/r). Apart from Anatase (A) and Rutile (R) phases, there is Brookite (B) which has been evaluated less as photocatalyst in mixed-phase nanoTiO2 systems. In this work we present a sustainable solution process to synthesize tunable composition mixed-phase nanotitania photocatalysts in a continuously stirred tank reactor (CSTR) by modulating conditions like pH, CTiCl4 and time. In particular three mixed-phase TiO2 nanomaterials were produced, namely one predominantly anatase with brookite as minor component (A/b), one predominantly brookite with minor component rutile (B/r), and one predominantly rutile with minor component brookite (R/b) and evaluated as photocatalysts in the degradation of methyl orange. The three semiconducting nanomaterials were characterized by XRD and Raman spectroscopy to quantify the phase ratios and subjected to nano-morphological characterization by FE-SEM and TEM/HR-TEM. The new mixed-phase nanoTiO2 materials are shown to be endowed with large specific surface area, ranging from 90–125 m2 g−1, double of that of P25, to be mesoporous and be surface-rich in Ti–OH molecular groups varying from 12%–20% versus 4% for P25. These properties though impact the adsorptive capacity with R/b and B/r removing > 50% of MO but not photocatalytic activity. The latter depends on nanograined mixed-phase structure and not mere assembly of different phase nanoparticles. First-order rate constants reveal essentially equivalent photocatalytic activity for anatase nanocrystals with either rutile (P25) or brookite (this work) domains.

Enhanced Power Conversion Efficiency of Dye-Sensitized Solar Cells by Band Edge Shift of TiO2 Photoanode

By simple soaking titanium dioxide (TiO₂) films in an aqueous Na₂S solution, we could prepare surface-modified photoanodes for application to dye-sensitized solar cells (DSSCs). An improvement in both the open-circuit voltage (V_oc) and the fill factor (FF) was observed in the DSSC with the 5 min-soaked photoanode, compared with those of the control cell without any modification. The UV–visible absorbance spectra, UPS valence band spectra, and dark current measurements revealed that the Na₂S modification led to the formation of anions on the TiO₂ surface, and thereby shifted the conduction band edge of TiO₂ in the negative (upward) direction, inducing an increase of 29 mV in the V_oc. It was also found that the increased FF value in the surface-treated device was attributed to an elevation in the shunt resistance.

Photovoltaic Performance of Dye-Sensitized Solar Cells Containing ZnO Microrods

At an elevated temperature of 90 °C, a chemical bath deposition using an aqueous solution of Zn(NO₃)₂·6H₂O and (CH₂)₆N₄ resulted in the formation of both nanoflowers and microrods of ZnO on F-doped SnO₂ glass with a seed layer. The nanoflowers and microrods were sensitized with dyes for application to the photoelectrodes of dye-sensitized solar cells (DSSCs). By extending the growth time of ZnO, the formation of nanoflowers was reduced and the formation of microrods favored. As the growth time was increased from 4 to 6 and then to 8 h, the open circuit voltage (V_oc) values of the DSSCs were increased, whilst the short circuit current (J_sc) values varied only slightly. Changes in the dye-loading amount, dark current, and electrochemical impedance were monitored and they revealed that the increase in V_oc was found to be due to a retardation of the charge recombination between photoinjected electrons and I₃^- ions and resulted from a reduction in the surface area of ZnO microrods. A reduced surface area decreased the dye contents adsorbed on the ZnO microrods, and thereby decreased the light harvesting efficiency (LHE). An increase in the electron collection efficiency attributed to the suppressed charge recombination counteracted the decreased LHE, resulting in comparable J_sc values regardless of the growth time.

The double perovskite structure effect of a novel La2CuNiO6-ZnSe-graphene nanocatalytic composite for dye sensitized solar cells as a freestanding counter electrode

Currently, the development of sensitized solar cells (DSSCs) with high power conversion efficiency and low cost is a major challenge in the academic and industrial fields.

Reactive Porphyrin Adsorption on TiO2 Anatase Particles: Solvent Assistance and the Effect of Water Addition

The surface functionalization of metal oxide nanoparticles with complex organic molecules can lead to optoelectronically very different material properties, depending on whether adsorption occurs at the solid-gas or solid-liquid interface. Here, we report on two different approaches to decorate anatase TiO₂ nanoparticle powders with 2 H-tetraphenylporphyrin (2HTPP) molecules: (i) porphyrin adsorption in dispersions of organic liquids and (ii) gas-phase functionalization where evaporated porphyrin molecules attach to dehydrated particle surfaces in the absence of solvent molecules. In the latter case, a bottom-up approach is pursued to explore both the impact of organic solvent molecules and the impact of spurious water on the surface chemistry of porphyrin-sensitized TiO₂ nanoparticles. Vis diffuse reflectance and photoluminescence emission spectroscopy provide clear evidence for the promotion of interfacial reorganization processes of the adsorbate species by coadsorbed solvent molecules in liquids. Moreover, traces of spurious water were found to induce protonation-deprotonation reactions on the adsorbed porphyrins with a strong impact on the optical properties of the resulting hybrid materials.

Influence of anchoring group numbers in an efficient pyridine-anchor co-adsorbent of pyridinecarboxaldimine substituted aminonaphthalene on the performance of N719 sensitized solar cells

The anchoring group numbers in pyridine-anchor co-adsorbent has important effect on the performance of co-sensitized solar cells.

Synthesis and characterization of substituted Schiff-base ligands and their d10 metal complexes: structure-induced luminescence tuning behaviors and applications in co-sensitized solar cells

The structure-induced luminescence tuning behaviors of Schiff-base ligand based d¹⁰ metal complexes and their applications in co-sensitized solar cells.

Effect of different donor groups in bis(6-methoxylpyridin-2-yl) substituted co-sensitizer on the performance of N719 sensitized solar cells

The donor group of co-sensitizers has an important effect on the performance of co-sensitized solar cells.

Green-engineered all-substrate mesoporous TiO(2) photoanodes with superior light-harvesting structure and performance

Electrophoretic deposition (EPD) is employed successfully in a suspension of multicomponent TiO2 nanoparticulates of different sizes and morphologies to engineer a very robust bifunctional electrode structure for dye-sensitized solar cell (DSSC) applications that shows excellent light-harvesting and photoelectrochemical performance. Aqueous-synthesized anatase nanocrystallites and sub-micrometer-sized "sea urchin"-like rutile aggregates are formulated in a stable isopropanol suspension without resorting to binders or charging agents. Interestingly, extremely robust films are obtained because of the high surface reactivity, electrophoretic mobility, and unique morphology of the rutile aggregates. DSSCs built with the newly configured bifunctional electrode yielded a record efficiency (8.59 %) for EPD-fabricated devices without resorting to mechanical compression. Such green-engineered mesoporous electrode structures can be built on both metallic and plastic substrates and can find applications in various energy and environmental fields.

N,N′-Bis((6-methoxylpyridin-2-yl)methylene)-p-phenylenediimine based d10 transition metal complexes and their utilization in co-sensitized solar cells

New d¹⁰ transition metal complexes of ZnL, CdL and HgL enhanced the performance of DSSCs by co-sensitization with N719.