Electrochemistry of P450cin: new insights into P450 electron transfer

Electrochemistry of bacterial cytochrome P450cin (CYP176A) reveals that, unusually, substrate binding does not affect the heme redox potential, although a marked pH dependence is consistent with a coupled single electron/single proton transfer reaction in the range 6 < pH < 10.     

Alkylpyrrolidiniumtrialkoxysilyl iodides as organic iodide sources for dye-sensitised solar cells

Two new alkylpyrrolidiniumtriethoxysilyl iodides have been developed as iodide sources for DSSCs; the compound with an undecyl spacer between the siloxane and the pyrrolidinium moieties furnished higher open circuit voltages than the propyl analogue and higher efficiencies at low light intensity.     

Porphyrin dye-sensitised solar cells utilising a solid-state electrolyte

We describe a porphyrin dye-sensitised solar cell utilising a solid state electrolyte containing the I(-)/I(3)(-) redox couple, which yields a performance of 5.3% under moderate light intensity and 4.8% at full sun.     

Proton-coupled electron transfer in dye-sensitized solar cells: a theoretical perspective

The functionality of the proton-coupled electron transfer (PCET) model was tested on a squaraine-sensitized solar cell. The geometrical parameters, excitations, and electronic structures of free and Ti⁺⁴-bound squaraine dye were monitored using a set of pure and hybrid density functional theory (DFT) functionals with diffuse and polarization functions. The infrared spectra showed the dye-metal proton transfer. The UV-Vis spectra of unbound and bound squaraine dye using the pure functional (PBEPBE) are in excellent agreement with the experimental ones. The first photoexcited state charge transfer enhanced the charge density around the anchoring group of neat and bound squaraine dye. The injection of electronic charge into the titanium complex was confirmed by density of states (DOS) and natural bond orbital (NBO) analyses. The comparatively high total hyperpolarizability of the squaraine dye is indicative of a potent nonlinear optical (NLO) devise.     

Characterisation of electron transport and back reaction in dye-sensitised nanocrystalline solar cells by small amplitude laser pulse excitation

The characterisation of the transport and interfacial reaction of electrons in dye-sensitised nanocrystalline solar cells is complicated by the non-linearity of these processes. This problem has been overcome by superimposing small amplitude pulsed laser excitation on steady background illumination. The laser perturbation of the photostationary state is sufficiently small that the photocurrent and photovoltage responses can be fitted using constant values of the electron diffusion coefficient D_n and electron lifetime τ_n. Analytical and finite difference solutions of the continuity equation have been used to analyse the experimental photocurrent, photocharge and photovoltage transients, and the intensity dependence of D_n and of τ_n has been established by varying the bias illumination level, and hence the dc photocurrent density, j_dc. The intensity dependence of D_n (D_n∝j_dc^0.68) is attributed to trapping/detrapping involving a distribution of trapping levels. The intensity dependence of τ_n (τ_n∝j_dc^−0.62) may indicate that the back reaction of electrons with I₃⁻ is not first order in electron concentration. Other possible explanations are that the interfacial electron transfer rate constant depends on trap occupancy or on the rate of surface or bulk electron diffusion.     

Interface engineering for solid-state dye-sensitised nanocrystalline solar cells: the use of an organic redox cascade

We demonstrate the formation of a charge transfer cascade at a nanostructured TiO2/dye/polymer/molecular hole transport multilayer interface. Charge recombination dynamics at this interface are shown to be retarded when the ionisation potential of the polymer layer exceeds that of the molecular hole transport layer.     

Photosensitized electron transfer processes of nanocarbons applicable to solar cells

Photosensitized electron-transfer processes of nanocarbon materials hybridized with electron donating or electron accepting molecules have been surveyed in this tutorial review on the basis of the recent results reported mainly from our laboratories. As nano-carbon materials, fullerenes and single wall carbon nanotubes (SWCNTs) have been employed. Fullerenes act as photo-sensitizing electron acceptors with respect to a wide variety of electron donors; in addition, the fullerenes act as good ground state electron acceptors in the presence of light-absorbing electron donors such as porphyrins and phthalocyanines. In the case of SWCNTs, their ground states act as electron acceptor and electron donors, depending on the photosensitizers. For example, with respect to the photoexcited porphyrins and phthalocyanines, SWCNTs usually act as electron acceptors, whereas for the photoexcited fullerenes, SWCNTs act as electron donors. The diameter sorted semi-conductive SWCNTs have been used to verify the size-dependent electron transfer rates. For the confirmation of the electron transfer processes, the transient absorption methods have been widely used, in addition to the time-resolved fluorescence spectral measurements. The kinetic data thus obtained in solution are found to be quite useful to predict the efficiencies of photovoltaic cells constructed on semiconductor nanoparticle modified electrodes and their photocatalytic processes.     

On-line monitoring and active control of dye uptake in dye-sensitised solar cells

Real-time monitoring of dye loading (N3 and N719) under continuous flow conditions on TiO(2) photoanodes for dye-sensitized solar cells has been applied to quantitatively investigate dye uptake kinetics, demonstrating that static impregnation provides in all cases higher dye loading and, as a consequence, better working devices.     

Composite liquid crystal-polymer electrolytes in dye-sensitised solar cells: effects of mesophase alkyl chain length

The doping of polymer electrolytes (PEs) with liquid crystal (LC) materials has been shown to improve the performance of dye-sensitised solar cells (DSSCs). This is achieved by promoting ionic conduction and increasing optical path length through multiple-light scattering within the photovoltaic devices. In LCs, it is well known that the length of the alkyl chain plays an important role since the LC morphology and mesophase stabilisation depend strongly on the alkyl group. In this work, liquid crystal-polymer composite electrolytes (LC-PEs) are prepared using nematic LCs with different alkyl chain lengths. The morphology of the LC-PEs is investigated and correlated with their electrical properties. Subsequently, DSSCs are prepared using the LC-PEs as a direct example of its application. It is shown that increasing the alkyl chain length of the LCs reduces the efficiency of the solar devices. The longer alkyl chains are speculated to intertwine, thus trapping the mobile ions and reducing the bulk ionic conductivity. For the same reason, longer alkyl chain LCs are thought to be unable to passivate the TiO₂ surface through the adsorption of cyanobiphenyl groups and hence the higher probability of back recombination reaction between the electrons in TiO₂ and PE.     

Purification-free synthesis of a highly efficient ruthenium dye complex for dye-sensitised solar cells (DSSCs)

A novel Ru(II) sensitiser A597 containing the 4,4'-dioctylamido-2,2'-bipyridine ancillary ligand is synthesised without the need for purification steps. It shows an irreversible oxidation at 0.92 V in the cyclic voltammogram and an absorbtion at 539 nm in the UV-vis spectrum corresponding to an (1)MLCT transition. Preliminary DFT calculations reveal that the HOMO is localised on the ruthenium metal centre and the thiocyanate ligands, whereas the LUMO is predominantly on the 4,4'-carboxy-2,2'-bipyridine ligand. The ruthenium complex exhibits a maximum power conversion efficiency (7.25%) compared with the known Z907 (8.32%) in dye-sensitised solar cells.     

X-shaped oligothiophenes as a new class of electron donors for bulk-heterojunction solar cells

Four X-shaped oligothiophenes with different conjugation length were investigated as novel electron donors in single-layer bulk-heterojunction solar cells. The UV-vis absorption spectra of blends of compounds 1-4 with 1-(3-methoxycarbonyl)propyl-1-phenyl[6,6]C(61) show a remarkably red shift and broadening with increasing thiophene number at each of the four branches. The performance of the photovoltaic cells varied significantly with molecular structures of the four oligothiophenes. Conversion efficiencies increased from 0.008% to 0.8% with changing the electron donors from 1 to 4. The maximum incident photon-to-current conversion efficiency of the device based on 4 reaches 31.6%, much higher than those of three other compounds 1-3. Remarkable improvement of the device performance was achieved with increasing the substituted thiophene number. The results show that the photovoltaic effect is dependent on the structural characteristics and the film forming abilities of the X-shaped thiophenes.     

Charge transfer in organic molecules for solar cells: theoretical perspective

This tutorial review primarily illustrates rate theories for charge transfer and separation in organic molecules for solar cells. Starting from the Fermi's golden rule for weak electronic coupling, we display the microcanonical and canonical rates, as well as the relationship with the Marcus formula. The fluctuation effect of bridges on the rate is further emphasized. Then, several rate approaches beyond the perturbation limit are revealed. Finally, we discuss the electronic structure theory for calculations of the electronic coupling and reorganization energy that are two key parameters in charge transfer, and show several applications.     

Calculation of the vibrationally non-relaxed photo-induced electron transfer rate constant in dye-sensitized solar cells

In this paper we shall show how to calculate the single vibronic-level electron-transfer rate constant, which will be compared with the thermal averaged one. To apply the theoretical results to the dye-sensitized solar cells, we use a simple model to describe how we model the final state of the electron-transfer process. Numerical calculations will be performed to demonstrate the theoretical results.     

Nb2O5 as a new electron transport layer for double junction polymer solar cells

Nb(2)O(5) as a new electron transport layer (ETL) was used for double junction polymer solar cells. The Nb(2)O(5) ETL was prepared by spin coating a Nb(2)O(5) sol-gel solution onto the active layer of the optical front subcell. The double junction devices using Nb(2)O(5) ETL exhibit an open circuit voltage (V(oc)) of 1.30 V, which is close to the sum of the s of the individual subcells. The current density-voltage (J-V) simulation showed that the double junction device performance using Nb(2)O(5) as ETL could be significantly increased by reducing the series resistance (R(se)) and matching the current densities of the individual subcells.     

Photoinduced intramolecular electron transfer in ruthenium and osmium polyads: insights from theory

Ru(II) and Os(II) complexes (P) of [4'-(p-phenyl)]terpyridyl ligand (ptpy) derivatized with an electron acceptor (A) of the triphenylpyridinium (H3TP+) type have been recently proposed as functional models for electron-transfer (ET) processes in the context of artificial photosynthesis. These inorganic dyads, P-A, are expected to undergo intramolecular photoinduced ET to form a charge separated (CS) state of pivotal interest. To draw a complete picture of possible ET processes, the ground- and excited-state properties of these complexes, both in their native and monoreduced forms, have been studied by the means of density functional theory (DFT). A time-dependent-DFT approach (TDDFT) was used to interpret the electronic spectra, while additional spectroscopic measurements have been carried out in order to complete the available experimental information and to further confirm the theoretical issues. Besides the noticeable quantitative agreement between computed and experimental absorption spectra, our results allow us to clarify, by first principles, the actual nature and interplay of the electronic and geometrical coupling between the acceptor moiety and the photosensitizer. The possibility of a direct (optical) ET from the ground state to the targeted *[P+-A-] CS state is theoretically postulated and found to be consistent with available photophysical data (transient absorption spectroscopy). Concerning backward ET (from the CS state), the occurrence of a quinoidal-like electronic redistribution inherent to the photoreduced acceptor-ligand is proposed to favor efficient charge recombination.     

New insight into hydrogen bond-mediated electron transfer

<正>Electron transfer (ET) is one of the most fundamental processes in nature, biological systems, and optoelectronic devices. The in-depth ET investigations of synthetic materials are of great significance for the understanding of those occurring in natural systems. Mixed-valence (MV) compounds,consisting of two bridged redox motifs that are structurally identical but different in valence, provide an appealing     

A near-infrared porphyrin-based electron acceptor for non-fullerene organic solar cells

A star-shaped electron acceptor with porphyrin as core and rhodanine-benzothiadiazole as end groups linked with ethynyl units was developed for non-fullerene solar cells, in which a PCE of 1.9% with broad photo response was achieved when combining with a diketopyrrolopyrrole-polymer as electron donor.     

Perspectives on ab initio molecular simulation of excited-state properties of organic dye molecules in dye-sensitised solar cells

In this mini-review, we summarise and critique the emerging field of quantum-based molecular simulation of dye-sensitised solar cells (DSSCs), with particular focus on the deployment of organic-based dyes therein. We assess the underlying methodologies, including developments, pitfalls and challenges, whilst gauging predictive performance vis-à-vis experimental performance. The predictive capabilities of simulation methods with respect to elucidation of underlying methods is considered in the light of progress towards the ultimate goal of predictive in silico design of DSSCs, to complement hand-in-hand experimental approaches in the development of state-of-the-art DSSC devices.     

A microelectrode study of triiodide diffusion coefficients in mixtures of room temperature ionic liquids, useful for dye-sensitised solar cells

The diffusion coefficients of triiodide in binary mixtures of ionic liquids at 25 ± 0.05 °C were determined via steady-state cyclic voltammetry at platinum disk microelectrodes in five different electrolyte systems, all representing potential ionic liquid based electrolytes for dye-sensitised solar cells. These electrolytes were composed of iodine, 1-methyl-3-propylimidazolium iodide (acting as iodide source) and a second lower viscous ionic liquid, namely 1-ethyl-3-methylimidazolium dicyanamide, 1-ethyl-3-methylimidazolium tetrafluoroborate or 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) and were investigated either at fixed ionic liquid composition and varying iodine concentration or at fixed iodine concentration and varying 1-methyl-3-propylimidazolium iodide content. To check and optimise our measurement set-up, four Pt disk microelectrodes with four different electrode radii (0.3–5 μm) were tested at a well known system (ferrocene/tetraethylammonium tetrafluoroborate/acetonitrile solutions). The radius of each electrode was controlled by scanning electron microscopy at the beginning and during the work. Correspondence: H. J. Gores, Institut für Physikalische und Theoretische Chemie der Universit?t, 93053 Regensburg, Germany     

New A-A-D-A-A-type electron donors for small molecule organic solar cells

Two A-A-D-A-A-type molecules (BCNDTS and BDCDTS), where two terminal electron-withdrawing cyano or dicyanovinylene moieties are connected to a central dithienosilole core through another electron-accepting 2,1,3-benzothiadiazole block, have been synthesized, characterized, and employed as electron donors for small molecule organic solar cells. Vacuum-deposited bilayer and planar mixed heterojunction devices based on BCNDTS and fullerene acceptors (C(60) or C(70)) exhibited decent power conversion efficiencies of 2.3% and 3.7%, respectively.