Dye-sensitized Nanocrystalline Semiconductor Research Articles

Recent Progress of Graphene-Based Photoelectrode Materials for Dye-Sensitized Solar Cells

Graphite with a single atomic layer known as graphene shows great capability in energy conversion and storage devices. Dye-sensitized solar cells (DSSCs) have attracted intense interests due to offering high photo-to-electric conversion efficiencies. DSSCs are built from a photoelectrode (a dye-sensitized nanocrystalline semiconductor), an electrolyte with redox couples, and a counterelectrode. In this review article, we outline the strategies to enhance the efficiency and reduce the cost by introducing graphene into the DSSCs as the photoelectrode. First, the development of DSSCs and the properties of graphene are briefly described. Then, the applications of graphene-based materials for photoelectrodes (transparent electrode, semiconductor layer, and dye sensitizer) in DSSCs are deeply discussed. Finally, an outlook for graphene materials in DSSCs is provided.

Exciton annihilation in dye-sensitized nanocrystalline semiconductor films

Exciton annihilation in dye-sensitized nanocrystalline semiconductor (Al2O3) films has been studied through laser-induced fluorescence spectroscopy. The relative quantum yield of the fluorescence decreases with increasing excitation light intensity, the indication being that exciton annihilation occurred. The rate constants of the annihilation were estimated for three dyes, N719, D149, and MK2, that are known to be sensitizing dyes for efficient dye-sensitized solar cells. The hopping time between dye molecules and the diffusion length of excitons within their lifetime were also estimated to facilitate discussion of the relevance of exciton annihilation to primary processes in dye-sensitized solar cells.

Fabrication of thin film nanocrystalline TiO2 solar cells using ruthenium complexes with carboxyl and sulfonyl groups

Two ruthenium complexes with carboxyl and sulfonyl groups have been synthesized, [RuII(L1)2(NCS)2] RuIIbis(4,7-diphenyl-1,10-phenanthroline-disulfonic acid disodium salt)-di(thiocyanate) [K313], [RuII(L1)2(dcbpy)] RuII bis(4,7-diphenyl-1,10-phenanthroline-disulfonic acid disodium salt)(4,4′-dicarboxy-2,2′-bipyridyl) [K314] as photosensitizers. UV–vis, fluorescence emission, AFM and CV measurements are also supplied for ruthenium complexes. Photovoltaic properties of dye sensitized nanocrystalline semiconductor solar cells based on Ruthenium complexes which bear carboxyl and sunfonyl groups have been tested under standard AM 1.5 sunlight. Under the standard global AM 1.5 solar conditions, K314 and K313-sensitized solar cells demonstrate short circuit photocurrent densities of 14.92mA/cm2 and 11.23mA/cm2 and overall conversion efficiencies of 5.09% and 4.02%, respectively.

Dye-Sensitized Nanocrystalline ZnO Solar Cells Based on Ruthenium(II) Phendione Complexes

The metal complexes ( (phen)2(phendione))(PF6)2(1), [ (phen)(bpy)(phendione))(PF6)2(2), and ( (bpy)2(phendione))(PF6)2(3) (phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine and phendione = 1,10-phenanthroline-5,6-dione) have been synthesized as photo sensitizers for ZnO semiconductor in solar cells. FT-IR and absorption spectra showed the favorable interfacial binding between the dye-molecules and ZnO surface. The surface analysis and size of adsorbed dye on nanostructure ZnO were further examined with AFM and SEM. The AFM images clearly show both, the outgrowth of the complexes which are adsorbed on ZnO thin film and the depression of ZnO thin film. We have studied photovoltaic properties of dye-sensitized nanocrystalline semiconductor solar cells based on Ru phendione complexes, which gave power conversion efficiency of (η) of 1.54% under the standard AM 1.5 irradiation (100 mW cm−2) with a short-circuit photocurrent density () of 3.42 mA cm−2, an open-circuit photovoltage () of 0.622 V, and a fill factor (ff) of 0.72. Monochromatic incident photon to current conversion efficiency was 38% at 485 nm.

Dye Sensitization of Single Crystal Semiconductor Electrodes

Even though investigations of dye-sensitized nanocrystalline semiconductors in solar cells has dominated research on dye-sensitized semiconductors over the past two decades, single crystal electrodes represent far simpler model systems for studying the sensitization process with a continuing train of studies dating back more than 40 years. Even today single crystal surfaces prove to be more controlled experimental models for the study of dye-sensitized semiconductors than the nanocrystalline substrates. This Account analyzes the scientific advances in the model sensitized single crystal systems that preceded the introduction of nanocrystalline semiconductor electrodes. It then follows the single crystal research to the present, illustrating both their striking simplicity of use and clarity of interpretation relative to nanocrystalline electrodes. Researchers have employed many electrochemical, photochemical, and scanning probe techniques for studying monolayer quantities of sensitizing dyes at specific crystallographic faces of different semiconductors. These methods include photochronocoulometry, electronic spectroscopy, and flash photolysis of dyes at potential-controlled semiconductor electrodes and the use of total internal reflection methods. In addition, we describe the preparation of surfaces of single crystal SnS(2) and TiO(2) electrodes to serve as reproducible model systems for charge separation at dye-sensitized solar cells. This process involves cleaving the SnS(2) electrodes and a photoelectrochemical surface treatment for TiO(2) that produces clean surfaces for sensitization (as verified by AFM) resulting in near unity yields for electron transfer from the molecular excited dyes into the conduction band. In recent experiments with ruthenium complexes at TiO(2) and with carboxylated cyanine dyes, we demonstrate the promise of this simple model for understanding dye-sensitized solar cells. In each of these systems, we can observe and analyze the complex photochemistry in a quantitative manner. Molecules of the well-known N3 ruthenium complex attach to four different crystallographic faces of anatase and rutile TiO(2) at different rates and to a different extent. With carboxylated cyanine dye sensitizers on these surfaces, molecular aggregation on the surface is a function of molecular structure and crystallographic face. In contrast with the N3 sensitizer these organic dyes undergo a photoinduced dimerization and desorption reaction when hydroquinone regenerators are present. With both classes of sensitizers, we demonstrate a new photochronocoulometric technique that quantifies the amount of attached dye on the electrode surface. We have completed initial experiments examining quantum dot sensitization of TiO(2) crystals, which could eventually lead to sensitizers with higher stability and absorption coefficients. Although these single crystal electrode models show promise for providing insights and predictive value in understanding the sensitization process, more sophisticated models will be needed to fully understand the charge transfer from the localized electronic states of the sensitizer to the extended states of the semiconductor.

Transparent solar cells based on dye‐sensitized nanocrystalline semiconductors

AbstractLow‐cost dye‐sensitized solar cells have attracted much attention because of their unique characteristics of transparency and various colors. A dye‐sensitized solar cell is composed of a dye‐coated nanocrystalline wide‐bandgap semiconductor, redox electrolyte and platinum counter‐electrode. Transparency and various colors are attributed to a 10–20 μm thick semiconductor film with particle size of about 10–20 nm and a difference in HOMO–LUMO energies of the dye molecules, respectively. A biomimetic working principle enables effective electron injection and regeneration. Recent research on dye‐sensitized solar cells has been focused on the improvement of solar‐to‐electricity conversion efficiency as well as long‐term stability. In this report, the recent advances of transparent solar cells based on dye‐sensitized semiconductors are reviewed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis and Modeling of Acridine Dyes as Potential Photosensitizers for Dye‐Sensitized Photovoltaic Applications†

We have synthesized novel aromatic amine‐substituted acridine dyes as potential candidates for the photosensitizers in dye sensitized nanocrystalline semiconductor based solar cells (DSSC) cells. The protonation and quaternization of the acridine nitrogen led to acridine dyes with extended absorption from 400–800 nm. Computational modeling was used to evaluate a variety of structures to achieve insights for correlating these types of molecular structures with predicted absorption spectra. Pertinent dihedral angles as well as bond lengths were evaluated to assess and compare planarity and conjugation for these dyes. Other predictions include plots of the HOMO and LUMO levels to qualitatively examine electron distributions and the potential for electron injection. The results from modeling along with the experimental data consisting of synthesis, characterization and UV‐visible absorption properties of the selected dyes are presented. †Dedicated to the memory of Professor Sukant K. Tripathy.

ELECTRON INJECTION AT DYE-SENSITIZED SEMICONDUCTOR ELECTRODES

Electron injection at dye-sensitized semiconductors is reviewed. Particular emphasis is placed on theoretical and photoelectrochemical studies of dye-sensitized planar and single-crystal electrodes. The accepted mechanism of electron injection, which was derived from these classical studies, is introduced. Selected photoelectrochemical studies of dye-sensitized nanocrystalline semiconductors are reviewed; emphasis is given to factors that influence the efficiencies of electron injection and charge recombination. The development of quasi-solid-state nanocrystalline dye-sensitized solar cells is also discussed. Recent time-resolved spectroscopic studies of electron injection and charge recombination are reviewed. These studies have led to a better understanding of electron injection mechanisms, and have revealed the limitations of the classical models.

Mechanism of Molecular Control of Recombination Dynamics in Dye-Sensitized Nanocrystalline Semiconductor Films

Recent experiments have shown that it is possible to switch between electron transport limited and interfacial electron transfer (IET) limited recombination dynamics of photoinjected electrons and the oxidized dye molecules anchored to the TiO2 under the same spectroscopic conditions, by appropriate design of the dye. The kinetics not only is slower in the IET limited case but also single exponential, in contrast to the highly dispersive transport limited recombination kinetics. We suggest that exponential kinetics could be a result of the Coulomb trap effect. Once an electron reaches the cation, electrostatic interaction keeps it near the cation until recombination takes place. Otherwise, dispersive transport would not allow for the exponential kinetics to develop. An analytical expression for the cation survival probability is derived that shows very good agreement with available experimental data. Physically, the Coulomb trap effect is justifiable if the relative dielectric constant of the surrounding ...

Kinetics and mechanism of electron injection and charge recombination in dye-sensitized nanocrystalline semiconductors

Kinetics and mechanism of electron injection and charge recombination in dye-sensitized nanocrystalline semiconductors

Photoinduced intra-molecular electron transfer in aniline-containing Ru(II) polypyridine complexes

The photoinduced intra-molecular electron transfer in three aniline-containing Ru(II) polypyridine complexes, [Ru(bpy) 2(bpy-bmam)](PF 6) 2 ( 2), Ru(dcbpy)(bpy-bmam)(NCS) 2 ( 3), and Ru(dcbpy)(bpy-mam)(NCS) 2 ( 4) (bpy-bmam=4,4′-bis( N-methyl-anilinomethyl)-2,2′-bipyridine, bpy-mam=4-methyl-4′-( N-methyl-anilinomethyl)-2,2′-bipyridine, dcbpy=4,4′-dicarboxyl-2,2′-bipyridine, bpy=2,2′-bipyridine), was investigated using steady-state and time-resolved absorption and emission spectra, and photoinduced inter-molecular electron transfer between [Ru(bpy) 2(dmbpy)](PF 6) 2 ( 1) (dmbpy=4,4′-dimethyl-2,2′-bipyridine) and N, N-dimethylaniline was also studied for comparison. While inter-molecular reductive quenching of 1’s emission by aniline was less efficient, nearly half emission was quenched intra-molecularly in 2. Upon photoinduced electron injection onto the conduction band of TiO 2 from 3 or 4 anchored on the TiO 2 surface, intra-molecular electron transfer from aniline moiety to Ru(III) orbital occurred rapidly with rate constants of 3.4×10 7 and 2.6×10 7 s −1, respectively, restricting the interfacial recombination of injected electrons with Ru(III) and as a result improving the photoelectrochemical behavior of 3 or 4 when used in dye-sensitized nanocrystalline semiconductor solar cells.

Mechanism of Charge Recombination in Dye-Sensitized Nanocrystalline Semiconductors: Random Flight Model

The trap-filling effect on the kinetics of charge recombination in dye-sensitized TiO2 nanoparticles is discussed on the basis of the random flight model. The model assumes that electrons move betw...

Dye-Sensitized Nanocrystalline TiO2 Solar Cells Based on Ruthenium(II) Phenanthroline Complex Photosensitizers

We have synthesized four carboxylated Ru(II) phenanthroline complexes with different numbers of carboxyl groups, cis-bis(4,7-dicarboxy-1,10-phenanthroline)dithiocyanato ruthenium(II) (Ru(dcphen)2(NCS)2), cis-bis(4-monocarboxy-1,10-phenanthroline)dithiocyanato ruthenium(II) (Ru(mcphen)2(NCS)2), cis-(4,7-dicarboxy-1,10-phenanthroline)(1,10-phenanthroline)dithiocyanato ruthenium(II) (Ru(dcphen)(phen)(NCS)2), and cis-(4-monocarboxy-1,10-phenanthroline)(1,10-phenanthroline)dithiocyanato ruthenium(II) (Ru(mcphen)(phen)(NCS)2), as photosensitizers for oxide semiconductor solar cells. We have studied photovoltaic properties of dye-sensitized nanocrystalline semiconductor solar cells based on Ru phenanthroline complexes and an iodine redox electrolyte. The photovoltaic performance of the TiO2 solar cell sensitized by Ru(dcphen)2(NCS)2(TBA)2 exceeded that of ZnO, SnO2, and In2O3 solar cells. A solar energy to electricity conversion efficiency (η) of 6.6% was obtained under the standard AM 1.5 irradiation (100 mW cm...

Photoelectric Response from Nanofibous Membranes

ABSTRACTElectrospinning has been used to prepare nanofibrous composite membranes of semi-conducting particles (TiO2) and photovoltaic dyes. Electrospinning is a relatively simple technique where electrical forces are used on polymeric solutions to produce nanoscale fibers. The resulting nanofibrous membranes have surface areas that are roughly one to two orders of magnitude higher than conventional thin films. It is believed that this higher surface will allow for more efficient light harvesting in photovoltaic devices. Our research has focused on the fabrication of organic/inorganic hybrid solar cells featuring dye sensitized nanocrystalline semiconductor particles using electrospinning. Phthalocyanine and N3 (cisdi(thiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylate) ruthenium(II)) photoactive dyes were electrospun with semi-conductive TiO2 nanoparticles into a matrix polymer, polyacrylonitrile (PAN). Electron microscopy and elemental analysis of the electrospun membranes shows that each component is present and uniformly dispersed in the nanofibrous membranes. In general, the dye membranes electrospun with the TiO2 nanoparticles exhibited a greater photoelectric response than the membranes with dye only. The N3 dye membranes however showed the greatest photoresponse in comparison to the phthalocyanine dyes, with or without the TiO2 nanoparticles. Photoelectric responses on the order of 30 μA and 280 mV were achieved with dye-sensitized membranes and are believed to be the first demonstration of a photoelectric response from an electrospun nanofibrous membrane.

Band Edge Movement and Recombination Kinetics in Dye-Sensitized Nanocrystalline TiO2 Solar Cells: A Study by Intensity Modulated Photovoltage Spectroscopy

The charge-recombination kinetics and band edge movement in dye-sensitized nanocrystalline TiO2 solar cells are investigated by intensity modulated photovoltage spectroscopy (IMVS). A theoretical model of IMVS for dye-sensitized nanocrystalline semiconductor electrodes is developed, and analytical expressions for the frequency dependence of the photovoltage response at open circuit are derived. The model considers charge trapping/detrapping and electron transfer from the conduction band and surface states of the semiconductor to redox species at the solid/solution interface. IMVS is shown to be valuable in elucidating the contributions of band edge shift and recombination kinetics to changes of the open-circuit photovoltage (Voc) resulting from surface modifications of the semiconductor. IMVS measurements indicate that surface treatment of [RuL2(NCS)2] (L = 2,2‘-bipyridyl-4,4‘-dicarboxylic acid)-sensitized TiO2 electrodes with 4-tert-butylpyridine or ammonia leads to a significant band edge shift concomit...