Review—Single-Walled Carbon Nanohorn-Based Dye-Sensitized Solar Cells

Efforts in the broad field of dye-sensitized solar cells (DSSC) are governed by four key challenges: i) the development of photoelectrodes with high charge injection yields and charge collection efficiencies, ii) the development of low-cost buffer layers, which effectively reduce the back reaction of electrons from the transparent conductive oxide (TCO) to the electrolyte, iii) the design of platinum-free counter electrodes (CE), which feature good electrolyte regeneration yields, and iv) the implementation of (quasi) solid-state and iodine-free electrolytes featuring excellent ionic diffusion and conductivity. The introduction of nanocarbons into each component of DSSCs has emerged as a promising strategy to tackle all the aforementioned challenges. Leading examples of nanocarbons are graphene, carbon black (CB), multi-walled carbon nanotubes (MWCNT), and single-walled carbon nanotubes (SWCNT). Here, we focus on single-walled carbon nanohorns (SWCNH), which were successfully integrated into each of the aforementioned parts of DSSCs

Expanding the Chemical Space of Tetracyanobuta-1,3-diene (TCBD) through a Cyano-Diels-Alder Reaction: Synthesis, Structure, and Physicochemical Properties of an Anthryl-fused-TCBD Derivative

Tetracyanobuta-1,3-diene (TCBD) is a powerful and versatile electron-acceptor moiety widely used for the preparation of electroactive conjugates. While many reports addressing its electron-accepting capability have appeared in the literature, significantly scarcer are those dealing with its chemical modification, a relevant topic which allows to broaden the chemical space of this interesting functional unit. Here, we report on the first example of a high-yielding cyano-Diels-Alder (CDA) reaction between TCBD, that is, where a nitrile group acts as a dienophile, and an anthryl moiety, that is, acting as a diene. The resulting anthryl-fused-TCBD derivative, which structure was unambiguously identified by X-ray diffraction, shows high thermal stability, remarkable electron-accepting capability, and interesting electronic ground- and excited-state features, as characterized by a thorough theoretical, electrochemical, and photophysical investigation. Moreover, a detailed kinetic analysis of the intramolecular CDA reaction transforming the anthryl-TCBD-based reactant into the anthryl-fused-TCBD product was carried out at different temperatures

A multicomponent molecular approach to artificial photosynthesis – the role of fullerenes and endohedral metallofullerenes

In this review article, we highlight recent advances in the field of solar energy conversion at a molecular level. We focus mainly on investigations regarding fullerenes as well as endohedral metallofullerenes in energy and/or electron donor–acceptor conjugates, hybrids, and arrays, but will also discuss several more advanced systems. Hereby, the mimicry of the fundamental processes occurring in natural photosynthesis, namely light harvesting (LH), energy transfer (EnT), reductive/oxidative electron transfer (ET), and catalysis (CAT), which serve as a blue print for the rational design of artificial photosynthetic systems, stand at the focalpoint. Importantly, the key processes in photosynthesis, that is, LH, EnT, ET, and CAT, define the structure of this review with the only further differentiation in terms of covalent and non-covalent systems. Fullerenes as well as endohedral metallofullerenes are chosen by virtue of their small reorganization energies in electron transfer processes, on the one hand, and their exceptional redox behaviour, on the other hand

Facile and quick preparation of carbon nanohorn-based counter electrodes for efficient dye-sensitized solar cells

For the first time, Pt-free counter electrodes based on carbon nanohorns for highly efficient dye-sensitized solar cells were assembled by a facile and fast drop cast technique. These novel electrodes feature an effective catalytic behavior towards the reduction of I3− and, as such, afford even higher short-circuit current densities compared to Pt-based references. In a final device, solar cells with 7.7% efficiency were achieved

Synthesis of Novel Porphyrin and its Complexes Covalently Linked to Multi-Walled Carbon Nanotubes and Study of their Spectroscopy

Novel covalent porphyrin and its complexes (Co2+, Zn2+) functionalized multi-walled carbon nanotubes (MWNTs) have been successfully synthesized by the reaction of the carboxyl on the surface of MWNTs which was synthesized to use carbon radicals generated by the thermal decomposition of azodiisobutyronitrile (AIBN) with 5-p-hydroxyphenyl-10,15,20-triphenyl-porphyrin and its complexes (Co2+, Zn2+). Three resulting nanohybrids were characterized by spectroscopy (FT-IR, Raman, and UV-vis), TGA, and TEM. The quality of porphyrin attached to the MWNTs was determined from thermogravimeric analysis (TGA) of the MWNTs, which showed a weight loss of about 60%. The Raman and absorption spectroscopy data showed that the electronic properties of modified MWNTs were mostly retained, without damaging their one-dimensional electronic properties. From fluorescence measurements, it was observed that the porphyrin and its complexes (Co2+, Zn2+) were nearly quenched by MWNTs, indicating that this covalently modified mode facilitated the effective energy or electron transfer between the excited porphyrin moiety and the extended π-system of MWNTs

Enhanced Performance of Dye-Sensitized Solar Cells based on TiO2 Nanotube Membranes using Optimized Annealing Profile

We use free-standing TiO2 nanotube membranes that are transferred onto FTO slides in front-side illuminated dye-sensitized solar cells (DSSCs). We investigate the key parameters for solar cell arrangement of self-ordered anodic TiO2 nanotube layers on the FTO substrate and namely the influence of the annealing procedure on the DSSC light conversion efficiency. The results show that using an optimal temperature annealing profile can significantly enhance the DSSC efficiency (in our case 9.8 %), as it leads to a markedly lower density of trapping states in the tube oxide, and thus to strongly improved electron transport properties

Clay-fulleropyrrolidine nanocomposites

In this work, we describe the insertion of a water-soluble bisadduct fulleropyrrolidine derivative into the interlayer space of three layered smectite clays. The composites were characterized by a combination of powder X-ray diffraction, transmission electron microscopy, X-ray photoemission and FTIR spectroscopies, and laser flash photolysis measurements. The experiments, complemented by computer simulations, give insight into the formation process, structural details, and properties of the fullerene/clay nanocomposites. The reported composite materials constitute a new hybrid system, where C-60 differs from its crystals or its solutions, and open new perspectives for the design and construction of novel C-60-based organic/clay hybrid materials.</p

Excited states and electron transfer reactions of C₆₀(OH)₁₈ in aqueous solution

Dynamic light scattering of fullerenol solutions [C60(OH)18] reveals evidence for the formation of fullerene aggregates at high solute concentration (up to 3.85×10-2 mol dm-3). This hydrophilic fullerene derivative emits very weak fluorescence regardless of its concentration. Photolysis (35 ps; &#955;ex=355 nm) of C60(OH)18 in aqueous solution yields the immediate formation of a transient singlet excited state with broad absorption in the 550–800 nm region with &#949;670nm=2130 d mol-1 cm-1. The energetically higher-lying singlet excited state transforms via intersystem crossing (i.e., with &#964;1/2=500 ps) to the also broadly absorbing (550-800 nm), triplet excited state. In contrast, at low solute concentration, the features of the (&#8727;T1&#8594;&#8727;Tn) absorption differ significantly exhibiting an absorption maximum at 650 nm concomitant to a shoulder at 570 nm. The &#960;-radical anion of fullerenol, [C60(OH)18]&#183;&#8722;, generated by electron transfer from hydrated electrons and (CH3)2C(OH) radicals, absorbs with &#955;max at 870, 980 and 1050 nm. Based on electron transfer studies with suitable electron donor/acceptor substrates, the reduction potential of the C60(OH)18/[C60(OH)18]&#183;&#8722; couple was estimated to be in the range between -0.358 and -0.465 V vs. NHE

Controlling electronic events through rational structural design in subphthalocyanine–corrole dyads: synthesis, characterization, and photophysical properties

Porphyrinoids are considered perfect candidates for their incorporation into electron donor–acceptor (D–A) arrays due to their remarkable optoelectronic properties and low reorganization energies. For the first time, a series of subphthalocyanine (SubPc) and corrole (Cor) were covalently connected through a short-range linkage. SubPc axial substitution strategies were employed, which allowed the synthesis of the target molecules in decent yields. In this context, a qualitative synthetic approach was performed to reverse the expected direction of the different electronic events. Consequently, in-depth absorption, fluorescence, and electrochemical assays enabled the study of electronic and photophysical properties. Charge separation was observed in cases of electron-donating Cors, whereas a quantitative energy transfer from the Cor to the SubPc was detected in the case of electron accepting Cors

En route towards panchromatic light harvesting: photophysical and electrochemical properties of Bodipy–porphyrazine conjugates

The concept of panchromatic light harvesting, that is, broad absorption cross sections throughout most of the visible range and excited state funnelling, has been realized in a novel set of porphyrazines. On one hand, zinc, copper, or magnesium ions were complexed by porphyrazines to tune their ground and excited state features. On the other hand, up to eight Bodipys were covalently attached to the periphery of the porphyrazines to enhance the ground state absorption. The corresponding star-shaped conjugates were probed by advanced photophysical measurements, that is, time-resolved fluorescence and femtosecond transient absorption spectroscopy. From the latter we derive spectroscopic and kinetic evidence in support of a fast and unidirectional energy transfer from the photoexcited Bodipy at the periphery to the porphyrazine at the core. In addition, the impact of the different metal centers is demonstrated