Larger Light-harvesting Efficiency Research Articles

Performance of dye-sensitized solar cells with mixed three natural pigments and reduced graphene oxide as a counter electrode

This work overviews the effect of combining three natural dyes as a photosensitizer for dye-sensitized solar cells (DSSC). Reduced graphene oxide in this work was used as a Pt-free counter electrode. The dyes consist of curcuminoid (Curcuma longa), chlorophyll (Justicia gendarussa), and anthocyanins (Clitoria ternatea). The effect of absorbance spectrum, Light Harvesting Efficiency (LHE), bandgap energy, and performance of DSSC were also studied. From the result, combination dyes have a broader absorbance spectrum and LHE than a single dyes solution, while the redox potential of the dye produces a similar gap energy (HOMO/LUMO) due to the solvent used to extract the dye, which is around 1.76–1.79 eV. The best result was achieved by a combination of three dyes, Yellow-Green-Blue, which has a short-circuit current density (Jsc) of 6.50 mA/cm2, an open-circuit voltage (Voc) of 0.94 V, a fill factor of 31.2 %, and efficiency of 1.91 %. The performance of the DSSC is not only due to a large amount of photon energy absorbed and adsorbed on the TiO2 surface and the fast electron diffusion rate due to the large LHE and narrow gap energy. Therefore, combining natural dye and using rGO as the counter electrode can improve the performance of DSSC optimally.

Theoretical design and characterization of D-A1-A based organic dyes for efficient DSSC by altering promising acceptor (A1) moiety

The electronic, optical and photovoltaic properties of dyes can be readily tuned by modifying the structure. Herein, the thieno[2,3-b]indole (Thi)-based molecules derived from dye NTU-2 (D-A1-A) have been designed by substituting BT by DPP(O), DPP(S), QuT and BBT units and dicyanovinylene by cyanoacetic acid. Based on density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, the regulation effect of acceptor groups on designed compounds was theoretically investigated. Indeed, in this context, the effects of various acceptor groups (A1) in D-A1-A dyes before and after binding to (TiO2)8 cluster on the electron injection have been studied. The optimized structures, electronic parameters, FMOs, NBO, PDOS analysis, the absorption spectra, and ICT parameters were evaluated to predict the suitable candidates for DSSC device. Our investigations reveal that all designed compounds have not only a significant λmax in the range of 593−824 nm, with a bandgap in the order, 2.31−1.56 eV, larger adsorption energies (Eads) and lower Λtotal, but also large light harvesting efficiency (LHE) and significant intramolecular charge transfer (ICT) properties compared to dye R. Accordingly, these theoretical calculations can provide an efficient strategy to design new promising sensitizers for DSSCs.

Solvent-dependent self-assembly of a ruthenium(II) complex bearing triazino-phenanthrenes and its applications in photocatalytic ascorbate fuel cells

The triazine-based metal-organic frameworks (MOFs) are of great significance in a photocatalytic or electrocatalytic system. This paper reports solvent-dependent self-assembly and photoelectrochemical properties of [Ru(ptp)2]2+ (ptp = 3-(1,10-phenanthrolin-2-yl)-as-triazino[5,6,f]phenanthrene) and its photoelectrocatalysis to ascorbate (AA) oxidation and oxygen reduction in photocatalytic fuel cells. [Ru(ptp)2]2+ can be dissolved in ethanol (E), ethanol/water mixtures (M), or water (W) to produce three forms of aggregates, which are further assembled into [Ru(ptp)2]2+ modified CdS photoanodes. The MOF form of [Ru(ptp)2]2+-M shows the maximum absorbance at ethanol/water of 1:1 (Ve/Vw), and the resulting [Ru(ptp)2]2+-M/CdS electrode has better conductivity, larger light-harvesting efficiency and photovoltaic response compared with that of [Ru(ptp)2]2+-E/CdS. Furthermore, [Ru(ptp)2]2+-M exhibits enhanced photoelectrocatalytic activity towards ascorbate oxidation and oxygen reduction. The simultaneous presence of [Ru(ptp)2]2+-M on CdS photoanode and single-walled carbon nanotubes (SWCNTs) cathode used in visible light-excited ascorbate fuel cells, leads to a 1.1-fold or 4.5-fold increase in the open-circuit voltage or maximum power density. This present study provides a significant platform for solvent-dependent self-assembly of triazino-phenanthrene-containing metal complexes and improvement of photocatalytic fuel cell performances.

Silole and selenophene-based D-π-A dyes in dye-sensitized solar cells: Insights from optoelectronic and regeneration properties

We report on the theoretical design of five new organic D−π−A sensitizers (JA1‒JA5) featuring silole and selenophene space π‒linker, and an evaluation of their performance for application in dye-sensitized solar cells (DSSCs). Their structural, spectral and electronic properties were investigated using density functional theory (DFT) and time-dependent (TD)-DFT calculations. We found that incorporation of a silole as a π‒bridge substituent in the five-membered heterocyclic dye, in particular to JA2 and JA4, remarkably improves the optical UV–Vis absorption spectra and achieves larger light-harvesting efficiency (LHE) relative to the conventional thiophene-based spacer (JA1), leading to a larger Jsc response. Interaction of these two theoretically designed dyes JA2 and JA4 in combination with iodide electrolytes was calculated and the LHE is significantly larger than that of their isolated dyes, both contribute to improving the DSSC performance. Calculated results give insight into the optoelectronic properties of the rationally substituted π-spacer D−π−A sensitizers concerning their regeneration and applicability for DSSCs.

Alcohol-Induced Synthesis of Photocatalytic TiO2 with Controlled Hierarchical Structure

Three-dimensional (3D) hierarchical TiO2 structures were obtained by a facile solvothermal process. Various analytical techniques were used to characterize the crystal phase, morphology and optical absorption of the obtained samples. The experimental results indicate that the morphology could be tailored by adjusting the volume ratio of glycerol to ethanol. The investigation of photocatalytic performance shows that all the as-prepared TiO2 samples possess an excellent photocatalytic activity superior to commercial P25 in the degradation of Rhodamine B (RhB) dye under UV-light irradiation. In addition, the optimized volume ratio of ethanol to glycerol is 20 : 15. The possible mechanism related to the photocatalytic activity of the sample is discussed in detail. The enhanced photocatalytic activities of TiO2 samples could result from their hierarchical structures assembled by 1D nanorods and large light-harvesting efficiency.

Theoretical insight on hybrid nanocomposites of graphene quantum dot and carbazole-carbazole dyes as an efficient sensitizer of DSSC.

The feasibility of the hybrid nanocomposites of the graphene quantum dot (GQD) and carbazole-carbazole dyes as the efficient sensitizer of dye-sensitized solar cells (DSSC) is investigated. By using the first principles density functional theory (DFT), we fully optimize the geometrical structures of GQD, the carbazole-carbazole dyes, and their hybrid nanocomposites. The harmonic frequency analysis is used to confirm the energy stability of the optimized structures. The optical absorptions of the structures are calculated with the time-dependent DFT (TDDFT). Using the I-/I3- electrolyte and the conduction band minimum of TiO2 electrode as a sample, we examine the feasibility of the nanocomposites as the sensitizer of DSSC with the charge spatial separation and the molecular orbital energy levels of the nanocomposites. The results demonstrate all the considered nanocomposites have suitable energy levels of the frontier orbitals and significantly charge spatial separation. TDDFT results show the oscillator strengths of all nanocomposites demonstrate the obvious enhancement in the visible light region. Moreover, the appropriate open-circuit voltage value, the larger light-harvesting efficiency, and larger driving force are also identified for these nanocomposites. Therefore, the nanocomposites could be the more promising candidates of sensitizer for DSSC in comparison with the separate carbazole-carbazole dyes.

Controlled preparation of TiO2 hollow microspheres constructed by crosslinked nanochains with high photocatalytic activity

TiO2 hollow microspheres were successfully synthesized via a controlled hydrolysis reaction, which involved the deposition of an inorganic coating of TiO2 on the surface of carbon spheres and subsequent removal of carbon spheres by calcination in air. The as-prepared TiO2 hollow microspheres with an average diameter of 200 nm presented a novel morphology, which was constructed by closely crosslinked TiO2 nanochains. The morphology of the hollow sphere can be controlled by varying the concentration of TiCl3 solution. A possible formation mechanism was also proposed. The photo-degradation of rhodamine B (RhB) aqueous solution showed that TiO2 hollow microspheres exhibited higher photocatalytic activity than that of TiO2 nanoparticles. The enhanced photocatalytic activity of the as-prepared TiO2 microspheres here could result from their hollow structures assembled by TiO2 nanochains and large light-harvesting efficiency.

Novel dipolar 5,5,10,10-tetraphenyl-5,10-dihydroindeno[2,1-a]-indene derivatives for SM-OPV: A combined theoretical and experimental study

In order to investigate the photo-physical, electrochemical, and optoelectronic properties of dipolar 5,5,10,10-tetraphenyl-5,10-dihydroindeno[2,1-a]-indene (TDI) derivatives, a facile synthesis has been developed to integrate arylamine (electron donor fragment, D) and aryl-2-methylenemalononitrile (electron acceptor fragment, A) into the TDI bridge. According to calculation results using the DFT/B3LYP/6-31G(d) method, the HOMO and LUMO energies of TDI derivatives are relevant to the extent of corresponding electron donating and accepting abilities, and influence the open-circuit voltage (Voc) and driving force (ΔE) in organic photovoltaics (OPV). The projected density of state (pDOS) analysis shows that the electron density distribution from the D fragment to TDI bridge in the HOMO is attributing to the electron-donating ability, whereas the electrons are mainly localized on A fragment in the LUMO. Calculations of the reorganization energy by the DFT/B3LYP/6-31G(d) method suggest these D-TDI-A derivatives are hole-transporting type materials. On the other hand, the calculated absorption spectra for these molecules in CH2Cl2 are simulated by using the TD-DFT/BH and HLYP/6-31G(d) method within the Polarizable Continuum Model (PCM) and provide the maximum absorption wavelength (λmax), which can be assigned to the HOMO to LUMO transition. HOMO is found to be the π orbital which is delocalized between the D fragment and the π-linker and LUMO is the π∗ orbital which is concentrated on the A fragment. The optical properties of D-TDI-A derivatives can be influenced by the D fragment and π-conjugated length. Calculated results of D-TDI-A derivatives also exhibited a large light harvesting efficiency related to the maximum absorption wavelength (RLHE)) and, according to these results, the D-TDI-A derivatives containing the Ab and Ad fragments would be useful electron donor materials for further development of new small molecular organic photovoltaic solar cell (SM-OPV) devices.

Theoretical study and design of triphenylamine-malononitrile-based p-type organic dyes with different π-linkers for dyes-sensitized solar cells

The geometries, electronic structures, absorption spectra and the character of excited state for the reported p-type sensitizers O2, O6 and O7 and designed 1–5 with different π-linkers were investigated by DFT and TDDFT calculations, to reveal the influences of π-linkers on the performance of DSSCs. It is found that the higher IPCE of O7 as compared to O6 stems from the improved light harvesting efficiency (LHE) and the efficient regeneration. And, for O2 and O6 with comparable IPCE, the slightly increased Jsc for O2 can be mainly ascribed to the better spectrum matching with solar spectrum. The results also revealed that the calculated charge transfer index (DCT, the metric of photoinduced electron–hole separation) for reported sensitizers is well correlated with the measured electron lifetime pertaining to Voc. Importantly, dye 4 may be a promising candidate for the p-type sensitizer due to the red-shifted absorption, larger LHE and longer DCT in comparison with prototype O7.

Broadband energy-harvesting hybrid solar cells employing nanocomposites of polythiophene:ternary PbSSe nanocrystals

Hybrid solar cells (HSCs) incorporating narrow band gap PbSSe nanocrystals (NCs) in a conjugated polymer were developed for the extensive use of solar radiation up to the near infrared (NIR) range. The developed cell, composed of poly(3-hexylthiophene) (P3HT):PbSSe NC composites with 1:1 weight ratio, exhibited a large light-harvesting efficiency over a broad range, in which the external quantum efficiency reached 0.3% at 1100 nm. These promising results were attributed to the well-assembled percolation networks with large interfacial junctions and the efficient use of broad solar spectrum due to the use of narrow band gap ternary NCs.

Hierarchical TiO2 spheres: facile fabrication and enhanced photocatalysis

Hierarchical TiO2 spheres were fabricated by means of Ti powders dissolved into HF solution following hydrothermal reaction with ammonia for the first time. The obtained TiO2 spheres had a good anatase structure and were composed of lots of nanoparticles and nanosheets. These hierarchical TiO2 spheres exhibited a high surface area and a large light harvesting efficiency. The photocatalytic activity of the hierarchical TiO2 spheres was determined by degradation of methylene blue in aqueous solution, and was compared to commercial P25 titania. It is revealed that the photocatalytic activity of hierarchical TiO2 spheres is enhanced a lot. The apparent rate constant of the hierarchical TiO2 spheres is as 1.5 times as that of P25 titania.

Fabrication and photocatalytical properties of flower-like TiO 2 nanostructures

Three-dimensional (3D) flower-like anatase TiO 2 nanostructures and flower-like titanate nanostructures were successfully synthesized via hydrothermal synthesis followed by post-treatment from titanium powder. The flower-like anatase TiO 2 nanostructures were characterized in detail with scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-vis spectrum and nitrogen adsorption-desorption measurement, respectively. It is found that the flower-like TiO 2 nanostructures have a high specific surface area and a large light-harvesting efficiency. The photocatalytical activity of the flower-like anatase TiO 2 nanostructures was determined by degradation of methylene blue in aqueous solution, and was compared with commercial P25 titania. It is revealed that the photocatalytical activity of the flower-like anatase TiO 2 nanostructures is enhanced a lot. The apparent rate constant of the flower-like anatase TiO 2 nanostructures is almost 2 times that of P25 titania.

Bis(2,2'-bipyridine)ruthenium(II)-hexacyanochromate(III) chromophore-luminophore complexes. Intramolecular energy transfer, excited-state intervalence transfer, and doublet-doublet annihilation

The binuclear (NC-Ru(bpy){sub 2}-NC-Cr(CN){sub 5}){sup 2{minus}} and trinuclear ((CN){sub 5}Cr-CN-Ru(bpy){sub 2}-NC-Cr(CN){sub 5}){sup 4{minus}} bimetallic complexes have been synthesized and their photophysical behavior has been studied. Visible light absorption by the Ru(bpy){sub 2}{sup 2+} chromophore leads to phosphorescence from the Cr(CN){sub 6}{sup 3{minus}} luminophore. The results demonstrate the occurrence of a fast ({tau} < 10 ns), efficient ({eta} = 1) intramolecular exchange energy transfer process from the MLCT triplet of the Ru(II) fragment to the doublet state of the Cr(CN){sub 6}{sup 3{minus}} fragment. Distinctive features of these chromophore-luminophore complexes with respect t the behavior of the isolated luminophore are as follows: (i) large light-harvesting efficiency (antenna effect); (ii) response to visible light (spectral sensitization); (iii) 100% efficient population of the emitting state; (iv) photostability. Intramolecular processes of the same type are probably responsible for the failure to observe doubly excited species upon two-photon excitation of the trinuclear complex.