Roles of electrolytes on charge recombination in dye-sensitized TiO(2) solar cells (2): the case of solar cells using cobalt complex redox couples

Dye-sensitized solar cells (DSC) were prepared from nanoporous TiO(2) electrodes with two different cobalt complex redox couples, propylene-1,2-bis(o-iminobenzylideneaminato)cobalt(II) {Co(II)(abpn)} and tris(4,4'-di-tert-buthyl-2,2'-bipyridine)cobalt(II) diperchlorate {Co(II)(dtb-bpy)(3)(ClO(4))(2)}. The performances of the DSCs were examined with varying the concentrations of the redox couples and Li cations in methoxyacetonitrile. Under 1 sun conditions, short-circuit currents (J(sc)) increased with the increase of the redox couple concentration, and the maximum J(sc) was found at the Li(+) concentration of 100 mM. To rationalize the observed trends of J(sc), electron diffusion coefficients and lifetimes in the DSCs were measured. Electron diffusion coefficients in the DSCs using cobalt complexes were comparable to the previously reported values of nanoporous TiO(2). Electron lifetime was independent of the concentration of the redox couples when the concentration ratio of Co(II)(L) and Co(III)(L) was fixed. With the increase of Li(+) concentration, the electron lifetime increased. These results were interpreted as due to their slow charge-transfer kinetics and the cationic nature of Co complex redox couples, in contrast to the anionic redox couple of I(-)/I(3)(-). The increase of the lifetimes with Li(+) was interpreted with the decrease of the local concentration of Co(III) near the surface of TiO(2). The addition of 4-tert-butylpyridine (tBP) with the presence of Li(+) increased J(sc) significantly. The observed increase of the electron lifetime by tBP could not explain the large increase of J(sc), implying that tBP facilitates the charge transfer from Co(II)(L) to dye cation, with the association of the change of the reorganization energy between Co(II) and Co(III).     

Effects of 4-tert-butylpyridine on the quasi-Fermi levels of TiO2 films in the presence of different cations in dye-sensitized solar cells

The effects of additives on the quasi-Fermi levels (QFL) of TiO(2) films in dye-sensitized solar cells (DSCs) were investigated by a direct method. We observed that the values of QFL of TiO(2) at short circuit and open circuit are different and found for the first time the linear relationships between QFL shifts at short circuit and open circuit induced by 4-tert-butylpyridine (TBP), and that the slopes of the lines were significantly influenced by the nature of cations in the electrolyte. Different QFL shifts at short circuit and open circuit were observed in the presence of TBA(+). These quantitative results suggest that the QFL of TiO(2) films at short circuit and open circuit can be adjusted separately by developing suitable additives and cations, which will be helpful to further improve the efficiency of DSCs.     

Tuning the HOMO energy levels of organic dyes for dye-sensitized solar cells based on Br-/Br3- electrolytes

A series of novel metal-free organic dyes TC301-TC310 with relatively high HOMO levels were synthesized and applied in dye-sensitized solar cells (DSCs) based on electrolytes that contain Br(-)/Br(3)(-) and I(-)/I(3)(-). The effects of additive Li(+) ions and the HOMO levels of the dyes have an important influence on properties of the dyes and performance of DSCs. The addition of Li(+) ions in electrolytes can broaden the absorption spectra of the dyes on TiO(2) films and shift both the LUMO levels of the dyes and the conduction band of TiO(2), thus leading to the increase of J(sc) and the decrease of V(oc). Upon using Br(-)/Br(3)(-) instead of I(-)/I(3)(-), a large increase of V(oc) is attributed to the enlarged energy difference between the redox potentials of electrolyte and the Fermi level of TiO(2), as well as the suppressed electron recombination. Incident photon to current efficiency (IPCE) action spectra, electrochemical impedance spectra, and nanosecond laser transient absorption reveal that both the electron collection yields and the dye regeneration yields (Φ(r)) depend on the potential difference (the driving forces) between the oxidized dyes and the Br(-)/Br(3)(-) redox couple. For the dyes for which the HOMO levels are more positive than the redox potential of Br(-)/Br(3)(-) sufficient driving forces lead to the longer effective electron-diffusion lengths and almost the same efficient dye regenerations, whereas for the dyes for which the HOMO levels are similar to the redox potential of Br(-)/Br(3)(-), insufficient driving forces lead to shorter effective electron-diffusion lengths and inefficient dye regenerations.     

Quantification of the effect of 4-tert-butylpyridine addition to I-/I3- redox electrolytes in dye-sensitized nanostructured TiO2 solar cells

Addition of 4-tert-butylpyridine (4TBP) to redox electrolytes used in dye-sensitized TiO2 solar cells has a large effect on their performance. In an electrolyte containing 0.7 M LiI and 0.05 M I2 in 3-methoxypropionitrile, addition of 0.5 M 4TBP gave an increase of the open-circuit potential of 260 mV. Using charge extraction and electron lifetime measurements, this increases could be attributed to a shift of the TiO2 band edge toward negative potentials (responsible for 60% of the voltage increase) and to an increase of the electron lifetime (40%). At a lower 4TBP concentration the shift of the band edge was similar, but the effect on the electron lifetime was less pronounced. The working mechanism of 4TBP can be summarized as follows: (1) 4TBP affects the surface charge of TiO2 by decreasing the amount of adsorbed protons and/or Li+ ions. (2) It decreases the recombination of electrons in TiO2 with triiodide in the electrolyte by preventing triiodide access to the TiO2 surface and/or by complexation with iodine in the electrolyte.     

Investigation of cation-induced degradation of dye-sensitized solar cells for a new strategy to long-term stability

Current-voltage characteristics, electron lifetimes (tau), and electron diffusion coefficients (D) of dye-sensitized TiO2 solar cells (DSCs) composed of liquid electrolytes were repeatedly measured over a period of time. It was found that the energy conversion efficiency of the DSCs using electrolytes composed of Li+ or tetrabutylammonium cation as the counter charges of I-/I3- redox couples decreased with the lapse of time. On the other hand, such a decrease was not observed for the DSC consisting of 1,2-dimethyl-3-propylimidazolium cation or of Li+ coupled with the addition of tert-butylpyridine. The decrease of the efficiency was in accordance with a decreased electron lifetime. The notable decrease in the presence of Li+ is probably caused by the excess amount of Li+ adsorption on the TiO2 surface.     

Bulk heterojunction photoelectrochemical cells consisting of oxotitanyl phthalocyanine nanoporous films and I(3)(-)/I(-) redox couple

Photoelectrochemical cells based on oxotitanylphthalocyanine (TiOPc) films and an I(3)(-)/I(-) redox couple have been constructed. The TiOPc films were prepared on an indium-tin oxide coated glass plate (ITO) by the micellar disruption method and characterized by their unique nanoporous structure. A photocurrent action spectrum for input radiation directed through the ITO/TiOPc film, film-thickness dependence, and morphological investigation revealed that the cells consisted of a bulk heterojunction formed between the nanoporous TiOPc films and the liquid I3-/I- electrolyte, resulting in a larger short-circuit current (J(sc)= 2.1 mA/cm(2)), open-circuit voltage (V(oc)= 0.11 V), fill factor (ff= 0.31), and hence a larger energy conversion efficiency (eta= 0.13% for an incident white-light intensity of 53 mW/cm2) than the bilayer structure composed of the vaccum-evaporated TiOPc compact film and the I(3)(-)/I(-) electrolyte (J(sc)= 0.16 mA/cm(2), V(oc)= 0.018 V, ff = 0.27, and eta = (1.5 x 10(-3)%).     

Stepped light-induced transient measurements of photocurrent and voltage in dye-sensitized solar cells: application for highly viscous electrolyte systems

To measure electron diffusion coefficients (D) and electron lifetimes (tau) of dye-sensitized solar cells (DSC), we introduced stepped light-induced transient measurements of photocurrent and voltage (SLIM-PCV), which can simplify the optical setup and reduce measurement time in comparison to conventional time-of-flight and frequency-modulated measurements. The method was applied to investigate the influence of the viscosity of a thermally stable high-boiling-point solvent on the energy conversion efficiency of DSCs. By systematic study of the influence of the viscosity, the species of cations as the counter charge of I(-)/I(3)(-), and the concentrations of electrolytes, we concluded that a lower dye cation reduction rate due to slower iodine diffusion is a limiting factor for a highly viscous electrolyte system. On the other hand, comparable values of D and increased values of tau were observed in a highly viscous electrolyte. By employing 0.5 M TBAI and 0.05 M I(2) in propylene carbonate, the efficiency of the DSC became comparable to that of a DSC using conventional electrolytes consisting of LiI, imidazolium iodide, and 4-tert-butylpyridine in methoxyacetonitrile. The simultaneous evaluation of D and tau through the appropriately simple measurement realizes fast optimization of the efficient and reliable DSC composed of thermally stable but often viscous electrolytes.     

Electron transport analysis for improvement of solid-state dye-sensitized solar cells using poly(3,4-ethylenedioxythiophene) as hole conductors

Dye-sensitized solar cells (DSCs) using solid-state hole conductor, poly(3,4-ethylenedioxythiophene) (PEDOT), were fabricated using in-situ photoelectrochemical polymerization giving short-circuit photocurrent density of 3.20 mA cm-2, open-circuit voltage of 0.77 V, and fill factor of 0.50, and the resulting overall conversion efficiency of 1.25% on average under air mass 1.5 conditions. Furthermore, the electron transport properties of the DSCs based on PEDOT (PEDOT/DSCs) were analyzed using light intensity modulation induced photocurrent and photovoltage decay (SLIM-PCV) measurements and electrochemical impedance spectroscopy (EIS) measurements, and then compared to those of the DSCs based on organic liquid electrolyte containing I-/I3- as redox couple (liquid iodide/iodine electrolyte-DSCs, iodide/DSCs for short). The effective filling of PEDOT in the mesopores of dyed TiO2 layers is an important key to achieve the respectable conversion efficiency of PEDOT/DSCs that is comparable with iodide/DSCs.     

Theoretical study of quinolines-I(2) intermolecular interaction and implications on dye-sensitized solar cell performance

The monomer and intermolecular charge-transfer complexes of 13 different quinoline derivatives with diiodine were studied using ab initio molecular orbital (MO) and density functional theory (DFT) methods. Calculations revealed that the sigma* orbital of iodine interacts with the nitrogen lone pair in the quinoline ring. The open-circuit photovoltage (V(oc)) values of an Ru(II) complex dye-sensitized nanocrystalline TiO(2) solar cell with an I(-)/I(3) (-) redox electrolyte in acetonitrile using quinoline additives were compared to the computational calculations on the intermolecular interaction between quinolines and I(2). The optimized geometries, frequency analyses, Mulliken population analyses, natural bond orbital (NBO) analyses, and interaction energies indicate that the V(oc) value of the solar cell is higher when quinoline complexes more favorably interact with I(2). Therefore, the interaction between the quinoline additives and iodine redox electrolyte is an important factor for controlling dye-sensitized solar cell performance.     

Panchromatic sensitization of nanocrystalline TiO2 with cis-Bis(4-carboxy-2-[2'-(4'-carboxypyridyl)]quinoline)bis(thiocyanato-N)ruthenium(II)

We compared the spectral (IR and Raman), electrochemical, and photoelectrochemical properties of nanocrystalline TiO(2) sensitized with the newly synthesized complex [NBu(4)](2)[cis-Ru(Hdcpq)(2)(NCS)(2)] (1; [NBu(4)](+) = tetrabutylammonium cation; H(2)dcpq = 4-carboxy-2-[2'-(4'-carboxypyridyl)]quinoline) with those of TiO(2) sensitized with [NBu(4)](2)[cis-Ru(Hdcbpy)(2)(NCS)(2)] (2; H(2)dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) and [NBu(4)](2)[cis-Ru(Hdcbiq)(2)(NCS)(2)] (3; H(2)dcbiq = 4,4'-dicarboxy-2,2'-biquinoline). Complex 1 achieved efficient sensitization of nanocrystalline TiO(2) films over a wide visible and near-IR region, generating a large short-circuit photocurrent. The absorbed photon-to-current conversion efficiency decreased in the order 2 > 1 > 3 with the decrease in the free energy change (-Delta G(inj)) of the electron injection from the ruthenium complex to TiO(2). The open-circuit photovoltages (V(oc)'s) of dye-sensitized solar cells decreased in the order 2 > 1 > 3 with the increase in the dark current resulting from reverse electron transfer from TiO(2) to I(3)(-). The sensitizer-dependent V(oc) value can be interpreted as a result of reverse electron transfer through the sensitizing dye molecules.     

Successful demonstration of an efficient I(-)/(SeCN)2 redox mediator for dye-sensitized solar cells

A new I(-)/(SeCN)(2) redox mediator has favorable properties for dye-sensitized solar cells (DSCs) such as less visible light absorption, higher ionic conductivity, and downward shift of redox potential than I(-)/I(3)(-). It was then applied for DSCs towards increasing energy conversion efficiency, giving a new potential for improving performance.     

Effect of additives on the photovoltaic performance of coumarin-dye-sensitized nanocrystalline TiO2 solar cells

The effects of deoxycholic acid (DCA) and 4-tert-butylpyridine (TBP) as additives on the photovoltaic performance of coumarin-dye-sensitized nanocrystalline TiO2 solar cells were investigated. DCA coadsorption improved both the photocurrent and photovoltage of the solar cells, even though it decreased the amount of dye adsorbed on the TiO2 electrode. The improved photocurrent may arise from suppression of the deactivation of the excited state via quenching processes between dye molecules or a more negative LUMO level of the dye in the presence of DCA, resulting in a high electron-injection yield from the dye into TiO2. The increased photovoltage is probably due to suppression of recombination between the injected electrons and I3- ions on the TiO2 surface (dark current). The addition of TBP to the electrolyte also markedly improved the photovoltage and fill factor of the solar cell, and consequently, the total conversion efficiency increased from 3.6% to 7.5%. FT-IR spectroscopy indicated that a large amount of TBP was adsorbed on the dye-coated TiO2 films in the presence of Li cations. This result suggests that TBP, like DCA, suppressed the dark current on the TiO2 surface, which resulted in the improved photovoltage.     

N3-sensitized TiO2 films: in situ proton exchange toward open-circuit photovoltage enhancement

Protons of N3, cis-bis(thiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylic acid)ruthenium(II), were in situ exchanged on N3-loaded TiO2 films with alkali-metal, tetrabutylammonium, and guanidinium cations. This simple strategy improved the open-circuit photovoltage (V(oc)) significantly, resulting in enhancement of the power conversion efficiency by 10-25%. Electrochemical impedance spectra revealed that the in situ proton exchange of the N3-loaded film suppressed charge recombination between injected electrons and I(3-) ions in the electrolyte, which, together with the negative shift of the conduction band edge for TiO2, may account for the remarkably increased V(oc) upon proton exchange of N3.     

Dye molecular structure device open-circuit voltage correlation in Ru(II) sensitizers with heteroleptic tridentate chelates for dye-sensitized solar cells

Dicarboxyterpyridine chelates with π-conjugated pendant groups attached at the 5- or 6-position of the terminal pyridyl unit were synthesized. Together with 2,6-bis(5-pyrazolyl)pyridine, these were used successfully to prepare a series of novel heteroleptic, bis-tridentate Ru(II) sensitizers, denoted as TF-11-14. These dyes show excellent performance in dye-sensitized solar cells (DSCs) under AM1.5G simulated sunlight at a light intensity of 100 mW cm(-2) in comparison with a reference device containing [Ru(Htctpy)(NCS)(3)][TBA](3) (N749), where H(3)tctpy and TBA are 4,4',4"-tricarboxy-2,2':6',2"-terpyridine and tetra-n-butylammonium cation, respectively. In particular, the sensitizer TF-12 gave a short-circuit photocurrent of 19.0 mA cm(-2), an open-circuit voltage (V(OC)) of 0.71 V, and a fill factor of 0.68, affording an overall conversion efficiency of 9.21%. The increased conjugation conferred to the TF dyes by the addition of the π-conjugated pendant groups increases both their light-harvesting and photovoltaic energy conversion capability in comparison with N749. Detailed recombination processes in these devices were probed by various spectroscopic and dynamics measurements, and a clear correlation between the device V(OC) and the cell electron lifetime was established. In agreement with several other recent studies, the results demonstrate that high efficiencies can also be achieved with Ru(II) sensitizers that do not contain thiocyanate ancillaries. This bis-tridentate, dual-carboxy anchor configuration thus serves as a prototype for future omnibearing design of highly efficient Ru(II) sensitizers suited for use in DSCs.     

Effect of iodine addition on solid-state electrolyte LiI/3-hydroxypropionitrile (1:4) for dye-sensitized solar cells

It was observed that the ionic conductivity of the solid-state electrolyte LiI/3-hydroxypropionitrile (HPN) = 1:4 (molar ratio) decreased dramatically with increasing iodine (I(2)) concentration, which differs from the conduction behavior of the Grotthuss transport mechanism observed in liquid or gel electrolytes. The short-circuit photocurrent density (J(sc)) of the dye-sensitized solar cell (DSSC) based on this electrolyte system increases with increasing I(2) concentration until LiI/I(2) is 1:0.05 (molar ratio). Beyond this limitation, the J(sc) decreases. At low I(2) concentrations (I(2)/LiI < or = 0.05), the J(sc) is mainly affected by the diffusion of I(3)(-). An increase of the I(2) concentration leads to the enhancement of the diffusion of I(3)(-) and an increase of the J(sc). At high I(2) concentrations (I(2)/LiI > 0.05), the factors, including the increased light absorption by the I(3)(-), the increased recombination of electrons at the photoanode with I(3)(-), and the reduced ionic conductivity of the electrolyte, lead to a decrease of J(sc). At the same time, the open-circuit voltage (V(oc)) of the DSSC decreases monotonically with the ratio of I(2)/LiI due to increased dark current in the DSSC. The increased absorption of visible light by the electrolyte, the enhanced dark current, and the reduced ionic conductivity of the electrolyte contribute to the performance variation of the corresponding solid-state DSSC with increasing I(2) concentration.     

Liquid-liquid distribution of ion-associates of dichlorocuprate(I) with quaternary ammonium counter-ions

The dichlorocuprate(I) anion CuCl(-)(2) can be extracted as its ion-associates Q(+).CuCl(-)(2) with quaternary ammonium cations (Q(+)) into chloroform. The extraction constants K(ex) have been determined, and the log K(ex) values found for the various counter-ions used are 1.93 for (C(3)H(7))(4)N(+), 4.10 for (C(4)H(9))(4)N(+), 6.57 for (C(5)H(11))(4)N(+), 1.57 for C(8)H(17)N(+) (CH(3))(3), 2.83 for C(10)H(21)N(+) (CH(3))(3) 4.12 for C(12)H(25)N(+) (CH(3))(3) and 5.21 for C(14)H(29)N(+)(CH(3))(3), respectively. A linear relationship was found between log K(ex) and the total number of carbon atoms in Q(+); from the slope of the line, the contribution of a methylene group to log K(ex) was calculated to be 0.59. The extractability with alkyltrimethylammonium cations was larger than that with symmetrical tetra-alkylammonium cations and the difference in log K(ex) for two cations (one of each type) with the same number of carbon atoms was about 0.4. From the extraction constants obtained, the extractability of CuCl(-)(2) was found to lie between that of ReO(-)(4) and ClO(-)(4).     

Influence of mesoporosity on lithium-ion storage capacity and rate performance of nanostructured TiO2(B)

Here, we present the Li(+) insertion behavior of mesoporous ordered TiO(2)(B) nanoparticles (meso-TiO(2)(B)). Using presynthesized 4 nm TiO(2)(B) nanoparticles as building blocks and a commercially available ethylene glycol-propylene glycol block copolymer (P123) as a structure-directing agent, we were able to produce mesoporous structures of high-purity TiO(2)(B) with nanocrystallinity and mesopore channels ranging from 10 to 20 nm in diameter. We compared the Li(+) insertion properties of nontemplated TiO(2)(B) nanoparticles (nano-TiO(2)(B)) to meso-TiO(2)(B) via voltammetry and galvanostatic cycling and found significant increases in overall Li(+) insertion capacity for the latter. While nano-TiO(2)(B) and meso-TiO(2)(B) both show surface charging (pseudocapacitive) Li(+) insertion behavior, meso-TiO(2)(B) exhibits a higher overall capacity especially at high charge rates. We attribute this effect to higher electrode/electrolyte contact area as well as the improved electron and ion transport in meso-TiO(2)(B). In this study, we have demonstrated the influence of both nanostructuring and mesoporosity on Li(+) insertion behavior by rationally controlling the overall architecture of the TiO(2)(B) materials.     

Photovoltage improvements and recombination suppression by montmorillonite addition to PEO gel electrolyte for dye-sensitized solar cells

Montmorillonite (MMT) added to electrolytes has been reported in the literature to facilitate the transport of I(-)/I(3)(-), and improve the ionic conductivity and consequent photocurrent of dye-sensitized solar cells (DSCs). This paper firstly observes, investigates and reports that MMT addition to a poly(ethylene oxide) (PEO)-based gel electrolyte not only improves the ionic conductivity of the gel electrolyte, but also increases the photovoltage and decreases the dark current. From the results of electrochemical impedance spectroscopy (EIS) and transient photovoltage spectra, we evidence that MMT in the polymer gel electrolyte can efficiently retard the charge recombination that occurs at the TiO(2)/dye/electrolyte interfaces.     

Ultrafast excited state dynamics controlling photochemical isomerization of N-methyl-4-[trans-2-(4-pyridyl)ethenyl]pyridinium coordinated to a {Re I(CO)3(2,2'-bipyridine)} chromophore

Two multifunctional photoactive complexes [Re(Cl)(CO)(3)(MeDpe(+))(2)](2+) and [Re(MeDpe(+))(CO)(3)(bpy)](2+) (MeDpe(+)=N-methyl-4-[trans-2-(4-pyridyl)ethenyl]pyridinium, bpy=2,2'-bipyridine) were synthesized, characterized, and their redox and photonic properties were investigated by cyclic voltammetry; ultraviolet-visible-infrared (UV/Vis/IR) spectroelectrochemistry, stationary UV/Vis and resonance Raman spectroscopy; photolysis; picosecond time-resolved absorption spectroscopy in the visible and infrared regions; and time-resolved resonance Raman spectroscopy. The first reduction step of either complex occurs at about -1.1 V versus Fc/Fc(+) and is localized at MeDpe(+). Reduction alone does not induce a trans-->cis isomerization of MeDpe(+). [Re(Cl)(CO)(3)(MeDpe(+))(2)](2+) is photostable, while [Re(MeDpe(+))(CO)(3)(bpy)](2+) and free MeDpe(+) isomerize under near-UV irradiation. The lowest excited state of [Re(Cl)(CO)(3)(MeDpe(+))(2)](2+) has been identified as the Re(Cl)(CO)(3)-->MeDpe(+ 3)MLCT (MLCT=metal-to-ligand charge transfer), decaying directly to the ground state with lifetimes of approximately 42 (73 %) and approximately 430 ps (27 %). Optical excitation of [Re(MeDpe(+))(CO)(3)(bpy)](2+) leads to population of Re(CO)(3)-->MeDpe(+) and Re(CO)(3)-->bpy (3)MLCT states, from which a MeDpe(+) localized intraligand (3)pipi* excited state ((3)IL) is populated with lifetimes of approximately 0.6 and approximately 10 ps, respectively. The (3)IL state undergoes a approximately 21 ps internal rotation, which eventually produces the cis isomer on a much longer timescale. The different excited-state behavior of the two complexes and the absence of thermodynamically favorable interligand electron transfer in excited [Re(MeDpe(+))(CO)(3)(bpy)](2+) reflect the fine energetic balance between excited states of different orbital origin, which can be tuned by subtle structural variations. The complex [Re(MeDpe(+))(CO)(3)(bpy)](2+) emerges as a prototypical, multifunctional species with complementary redox and photonic behavior.     

Improved performance in dye-sensitized solar cells employing TiO2 photoelectrodes coated with metal hydroxides

The performance of dye-sensitized solar cells (DSCs) was compared before and after processing the TiO(2) electrodes by minute-order electrochemical reactions with metal nitrates, where the metals were Mg, Zn, Al, and La, in 2-propanol. An overcoating of metal hydroxide was formed without the need for a sintering process, and magnesium hydroxide was found to give the largest improvement in photovoltage, fill factor, and eventually overall conversion efficiency of the DSCs. To analyze the nature of the improvement, the diffusion coefficient (D) and electron lifetime (tau) were determined. While little influence of overcoating on D was seen, a correlation between the increase in tau and V(oc) was observed for the metals examined here. The remarkable improvement in the electron lifetime of the DSCs suggests that an overcoating with magnesium hydroxide species function as the blocking layers at the fluorine-doped tin oxide and TiO(2) interfaces, thus contributing to the suppression of electron leakage, i.e., recombination processes between unidirectional transporting electrons and poly-iodides such as tri-iodide in the processed TiO(2) photoelectrode systems. The increase in V(oc) can be explained by the increased electron density caused by the increase in electron lifetime.