Nanocrystalline TiO2 Solar Cells Research Articles

Binary Polyethylene Oxide/Titania Solid-State Redox Electrolyte for Highly Efficient Nanocrystalline TiO2 Photoelectrochemical Cells

Poly(ethylene oxide)/titania polymer electrolyte based photoelectrochemical cells have been fabricated with Ru(dcbpy)2(NCS)2 complex as the sensitizer and nanoporous TiO2 films as photoanodes. The introduction of the titania filler into the poly(ethylene oxide) matrix reduces the crystallinity of the polymer and enhances the mobility of the I-/I3- redox couple, resulting in outstanding overall conversion efficiency (4.2% under direct sunlight illumination) of the corresponding dye-sensitized nanocrystalline TiO2 solar cell, one of the best efficiencies reported to date for a solid-state device.

High efficiency dye-sensitized nanocrystalline solar cells based on ionic liquid polymer gel electrolyte.

An ionic liquid polymer gel containing 1-methyl-3-propylimidazolium iodide (MPII) and poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) has been employed as quasi-solid-state electrolyte in dye-sensitized nanocrystalline TiO2 solar cells with an overall conversion efficiency of 5.3% at AM 1.5 illumination.

Low-Cost, Large-Area Nanocrystalline TiO2 -Polymer Solar Cells on Flexible Plastics

ABSTRACTThis paper describes our recent research on the development of fully flexible and low-cost dye-sensitized nanocrystalline TiO2 solar cells (DSSC). At EIC Laboratories, we have developed various large-area solid-state versions, which include both ionically, and hole-conducting allpolymer DSSCs made by continuous coating and lamination process. Various critical steps involve ∼10 micron thick nanocrystalline TiO2 film deposition on conducting PET plastics by various methods such as spraying, spin coating, and screen printing, a low temperature sintering (∼150°C) process, and polymer laminated electrolyte have been demonstrated as valuable active components. The photovoltaic (PV) performance presented in this paper show the fabricated solar cells of ∼1.2 cm2 area with reproducible AM1.5 (Air Mass 1.5) efficiencies of 4.7%. A prototype solar cell with a new hole conducting star polymer with AM 1.5 efficiency ∼2.12% has been thoroughly characterized and discussed.

Effect of the Ligand Structure on the Efficiency of Electron Injection from Excited Ru−Phenanthroline Complexes to Nanocrystalline TiO2 Films

We previously reported that the number of anchoring carboxyl groups affects the solar cell performance of dye-sensitized nanocrystalline TiO2 solar cells using Ru−phenanthroline complexes as the sensitizer. To understand the mechanism in detail, the electron injection efficiency of sensitizing dyes adsorbed on nanocrystalline TiO2 films has been studied by transient absorption spectroscopy. We found that the efficiency of electron injection is strongly affected by the number of carboxyl groups of the sensitizing dye, i.e., the efficiency of cis-bis(4,7-dicarboxy-1,10-phenanthroline)dithiocyanato ruthenium(II) (with four carboxyl groups) adsorbed on nanocrystalline TiO2 films (DCP2/TiO2) being 4 times as large as that of cis-(4-monocarboxy-1,10-phenanthroline)(1,10-phenanthroline)dithiocyanato ruthenium(II) (with one carboxyl group) adsorbed on the same films (MCPP/TiO2). From the analysis of the time profile of the transient absorption, we conclude that the low efficiency of MCPP/TiO2 is due to the presen...

A coumarin-derivative dye sensitized nanocrystalline TiO2 solar cell having a high solar-energy conversion efficiency up to 5.6%

It is found that newly synthesized coumarin derivatives work as highly efficient photosensitizers for dye-sensitized nanocrystalline TiO2 solar cells producing a 5.6% solar-light-to-electricity conversion efficiency, the highest efficiency so far among organic dye-sensitized solar cells, with a short-circuit current density of 13.8 mA cm−2, an open-circuit photovoltage of 0.63 V, and a fill factor of 0.63 under standard AM 1.5 irradiation (100 mW cm−2).

Spectral response and IV-characterization of dye-sensitized nanocrystalline TiO2 solar cells

Dye-sensitized nanocrystalline TiO2 solar cells (nc-DSCs) are based on a fundamentally different working principle than solar cells based on semiconductors. This could have implications for the characterization of nc-DSCs. In this study a comparison is made between two methods for determination of the spectral response of nc-DSCs. The standard method for determination of the spectral response according to the ASTM E1021-84 norm appears to be valid for the nc-DSC. The response of the solar cell to pulsed irradiation plays an important role in this determination, since pulsed illumination of the solar cell is involved. The response time of the nc-DSC is related to electron trapping in the TiO2 and depends on illumination conditions and also on chemical composition of the cell. For this reason, prior to measurements of spectral response of nc-DSCs, the response time of the cell should be measured under the same illumination conditions that are applied during spectral response measurements.

Effect of the Surface-State Distribution on Electron Transport in Dye-Sensitized TiO2 Solar Cells: Nonlinear Electron-Transport Kinetics

Analytical expressions describing electron transport in dye-sensitized nanocrystalline TiO2 solar cells are derived and verified by intensity-modulated photocurrent spectroscopy measurements. An exponential distribution of surface states can account for the observed power law dependence of the electron-transport rate on the electron population. Use of an effective electron diffusion coefficient to describe the electron transport kinetics is found to be inadequate. A slope of 69 meV is inferred for the surface-state distribution curve.

Intensity Dependence of the Back Reaction and Transport of Electrons in Dye-Sensitized Nanocrystalline TiO2Solar Cells

The lifetime τn and diffusion coefficient Dn of photoinjected electrons have been measured in a dye-sensitized nanocrystalline TiO2 solar cell over 5 orders of magnitude of illumination intensity using intensity-modulated photovoltage and photocurrent spectroscopies. τn was found to be inversely proportional to the square root of the steady-state light intensity, I0, whereas Dn varied with I00.68. The intensity dependence of τn is interpreted as evidence that the back reaction of electrons with I3- may be second order in electron density. The intensity dependence of Dn is attributed to an exponential trap density distribution of the form Nt(E) ∝ exp[−β(E − Ec)/(kBT)] with β ≈ 0.6. Since τn and Dn vary with intensity in opposite senses, the calculated electron diffusion length Ln = (Dnτn)1/2 falls by less than a factor of 5 when the intensity is reduced by 5 orders of magnitude. The incident photon to current efficiency (IPCE) is predicted to decrease by less than 10% over the same range of illumination in...

New platinum(II) polypyridyl photosensitizers for TiO2 solar cells

A square-planar platinum(II) based dye containing 4,4′-dicarboxy-2,2′-bipyridine and quinoxaline-2,3-dithiolate ligands achieves efficient sensitization of nanocrystalline TiO2 solar cells over a wide visible range, generating a short-circuit photocurrent of 6.14 mA cm−2 and an open-circuit potential of 600 mV under simulated AM 1.5 solar irradiation, with a solar energy conversion efficiency of 2.6%.

RU(II) sensitized Nb2O5 solar cell made by the sol-gel process

Since the development of dye sensitized nanocrystalline TiO2 solar cells by Grätzel et al., several other semiconducting electrode materials have been tested. The results obtained for solar cells of similar configuration using Nb2O5 layers are presented. 6μm thick Nb2O5 films have been deposited on conducting ITO or FTO glass by spin and dip coating process and sintered in air at 520°C. The layers are porous and crystalline with particle size ranging between 20 and 100 nm. Spectral sensitization of the films was carried out with a ruthenium(II)-complex, cis-Di(thiocyanato)-N,N′-bis(2,2′-bipyridyl-4,4′dicarboxylic acid)-ruthenium(II) dihydrate). The spectral incident photon to current conversion efficiency (IPCE) measured with a photoelectrochemical cell for a 4.9 cm2 electrode has a maximum value of 40% at 520 nm. Closed solar cells of different sizes have been built and their photocurrent, open circuit voltage, fill factor and efficiency have been measured under tungsten halogen lamp irradiation up to 1000 W/m2. The results obtained with a 0.2 cm2 closed cell for a 100 W/m2 (1/10 Sun) are isc=1.7 mA/cm2, Uoc=0.57 V, FF=0.55, η=5%. The conversion efficiency decreases with the light intensity. The influence of the Nb2O5 microstructure on the performance of the solar cell and a comparison with nanocrystalline TiO2 solar cell are presented.

Evaluation of the Charge-Collection Efficiency of Dye-Sensitized Nanocrystalline TiO2 Solar Cells

Intensity modulated photovoltage spectroscopy (IMVS) and intensity modulated photocurrent spectroscopy (IMPS) are used to evaluate the charge-collection efficiency of dye-sensitized nanocrystalline TiO2 solar cells. The charge-collection efficiency of the photoinjected electrons from dye sensitization is estimated from the respective time constants for charge recombination at open circuit τoc and the combined processes of charge collection and charge recombination at short circuit τsc obtained by IMVS and IMPS measurements. Three models are developed for relating the charge-collection efficiency to τoc/τsc. The first model determines the charge-collection efficiency from τoc/τsc without considering the underlying physical processes measured by IMVS and IMPS. The second model obtains τoc/τsc by simulating the frequency response of IMVS and IMPS from the time-dependent continuity equation for simplified conditions. The third model determines the time constants for IMVS and IMPS from electron-concentration p...

Estimation of the Charge-Collection Efficiency of Dye-Sensitized Nanocrystalline TiO2 Solar Cells*

Intensity modulated photovoltage spectroscopy (IMVS) and intensity modulated photocurrent spectroscopy (IMPS) are used to evaluate the charge-collection efficiency of dye-sensitized nanocrystalline TiO2 solar cells. The charge-collection efficiency of the photoinjected electrons from dye sensitization is estimated from the respective time constants for charge recombination at open circuit τoc and the combined processes of charge collection and charge recombination at short circuit τsc obtained by IMVS and IMPS measurements. Three models are developed for relating the charge-collection efficiency to τoc/τsc. The first model determines the charge-collection efficiency from τoc/τsc without considering the underlying physical processes measured by IMVS and IMPS. The second model obtains τoc/τsc by simulating the frequency response of IMVS and IMPS from the time-dependent continuity equation for simplified conditions. The third model determines the time constants for IMVS and IMPS from electron-concentration p...

Estimation of the Charge-Collection Efficiency of Dye-Sensitized Nanocrystalline TiO2 Solar Cells*

Article Estimation of the Charge-Collection Efficiency of Dye-Sensitized Nanocrystalline TiO2 Solar Cells* was published on January 1, 1998 in the journal Zeitschrift für Physikalische Chemie (volume 1, issue 1).

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...

Artificial Photosynthesis. 2. Investigations on the Mechanism of Photosensitization of Nanocrystalline TiO2 Solar Cells by Chlorophyll Derivatives

The mechanism of photosensitization of colloidal TiO 2 electrodes with chlorin e 6 and copper chlorophyllin is deduced from static and time-resolved fluorescence quenching as well as laser flash photolysis and photocurrent/ voltage transients in combination with cyclic voltammetry and spectroelectrochemistry. The fluorescence of chlorin e 6 on TiO 2 decays to 80% within 0.4 ns, indicating efficient electron injection from the singlet excited state with k et =2.2×10 9 s -1