Photoelectrochemical solar energy conversion based on blend of poly(3-hexylthiophene) and fullerene

A solid-state photoelectrochemical solar energy conversion device based on blend of poly(3-hexylthiophene) (P3HT) and fullerene (C₆₀) has been constructed and characterized. The photoelectrochemical performance parameters of the device were compared with pure P3HT solid-state photoelectrochemical cell. The current–voltage characteristics in the dark and under white light illumination and photocurrent spectra for front- and backside illuminations have been studied. The following device parameters were obtained: an open-circuit voltage of 97.8 mV and a short-circuit current of 7.28 μA/cm² at light intensity of 100 mW/cm²; IPCE% of 0.43% for front side illumination (ITO/PEDOT) and IPCE% of 0.01% for backside illumination (ITO/P3HT:C₆₀). The dependence of the short-circuit current and an open-circuit voltage on the light intensity and time have also been studied.     

A dye sensitized TiO2 photovoltaic cell constructed with an elastomeric electrolyte

A photovoltaic solar cell employing an elastomeric electrolyte and using a dye-sensitized nanoporous TiO₂ electrode has been assembled. The polymeric electrolyte is poly(epichlorohydrin-co-ethylene oxide) filled with NaI/I₂. This cell exhibits an open-circuit voltage of 0.71 V and a short-circuit current of 0.46 mA cm⁻² under 120 mW cm⁻² of white-light illumination. The overall conversion efficiency of the cell is 0.22%. The polymeric electrolyte behavior under different conditions of external resistance and intensity of light as well as the performance of this photoelectrochemical cell are discussed.     

Photosensitization of nanocrystalline TiO2 films by a polymer with two carboxylic groups, poly (3-thiophenemalonic acid)

Photovoltaic devices were assembled using a conducting polymer; poly (3-thiophenemalonic acid) sensitized TiO₂ electrodes and an electrolyte containing I₃⁻/I⁻ redox couple. This cell exhibited a short-circuit photocurrent (J_sc) of 6.65 mA cm⁻², an open circuit voltage (V_oc) of 355 mV and an efficiency of 1.5% under the illumination of 100 mW cm⁻² (AM 1.5). Addition of an ionic liquid, 1-methyl 3-n-hexylimidazolium iodide, into the electrolyte led to an improvement in the cell performances, achieving an overall efficiency of 1.8% under the same illumination. The average cell characteristics of the later devices are , with a fill factor of 0.65.     

Photoelectrochemical studies of the junction between poly[3-(4-octylphenyl)thiophene] and a redox polymer electrolyte

The photoelectrochemical properties of all-solid-state photoelectrochemical cell constructed from a conjugated polymer poly[3-(4-octylphenyl)thiophene] and an amorphous poly(ethylene oxide) complexed with iodide/triiodide redox couple were studied. In order to develop flexible photoelectrochemical cells, we have used a transparent polymeric metal, doped poly(3,4-ethylenedioxythiophene), as a counter electrode. It was shown that poly(3,4-ethylenedioxythiophene) improved the charge transfer between indium tin-oxide and iodide/triiodide redox couple. The spectral response, photocurrent time, and open-circuit voltage and short-circuit current dependence on light intensity have been studied. The photon to electron conversion efficiency obtained was low. The photocurrent and photovoltage dependence studies on light intensity indicate exciton recombination and/or traps as limiting factors.     

The obstructed diffusion of the I3 ion in mesoscopic TiO2 membranes

The diffusional permeability of I⁻₃ ion in acetonitrile in free standing TiO₂ membrane with a porosity of 55% was examined. The apparent diffusion coefficient, D_app at 25°C of the ion was found to be 3.4×10⁻⁶ cm^{2 −1}, an order of magnitude smaller than the free diffusion at the same temperature. The temperature dependency of D_app was measured in the range 0–30°C and analysed in terms of the Walden product. The diffusional activation energy was found to be 13.5 kJ/mol. The parameters of interest for the efficiency of mesoscopic wet solar cells are discussed. A back of an envelope calculation shows that although the obstructed diffusion coefficient of the I⁻₃ ion was an order of magnitude smaller than the free diffusion the diffusional flux is still sufficient to meet a current density of 50 mA cm⁻². At incident photon flux of 1 kW m⁻² and at a photopotential of 0.6 V this would correspond to a solar energy efficiency of approximately 30%.     

Characterization of N, N′-bis-2-(1-hydoxy-4-methylpentyl)-3, 4, 9, 10-perylene bis (dicarboximide) sensitized nanocrystalline TiO2 solar cells with polythiophene hole conductors

We have fabricated solid-state, dye-sensitized nanocrystalline TiO₂ solar cells (DSSC) based on perylene derivative dye, N,N′-bis-2-(1-hydoxy-4-methylpentyl)-3,4,9,10-perylene bis (dicarboximide) (HMPER) with two different polythiophenes as hole conductors; i.e. poly (3-octyl thiophene) (P3OT) and poly (3-hexyl thiophene) (P3HT), respectively. HMPER adsorbs strongly to the surface of nanocrystalline TiO₂ and inject electrons into TiO₂ conduction band upon absorption of light. Polythiophene derivatives are well-known materials as hole conductors in solid-state dye-sensitized solar cells. We obtained quite similar results with P3OT and P3HT yielding a short-circuit current density of around 80 μA/cm² and open-circuit voltage of around 0.7 V at 80 mW/cm² AM 1.5 light intensity. The results are compared with Ru-535 TBA-sensitized nc-TiO₂ cells prepared by using the same polythiophene derivatives.     

Comparative study of nanocrystalline TiO2 photoelectrodes based on characteristics of nanopowder used

A solid-state cell was fabricated by sandwiching poly[2-methoxy-5(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) in between micro-porous n-TiO₂ and p-CuI films. The photo-excited polymer is found inject electrons into the conduction band of n-TiO₂ and holes into the valance band of p-CuI. Maximum open-circuit voltage of 400 mV and short-circuit current of about 0.3 mA cm⁻² were observed for the TiO₂|MEH-PPV|CuI cell, under white light illumination (100 mW cm⁻²).     

Efficient hybrid carboxylated polythiophene/nanocrystalline TiO2 heterojunction solar cells

Efficient hybrid solar cells fabricated from TiO₂, novel carboxylated polythiophene poly (3-thiophenemalonic acid) P3TMA as sensitizer as well as hole conductor and poly (3-hexylthiophene) (P3HT) as hole transporter was described. UV-Vis absorption and morphology of the active layer were investigated. Device J/V characterizations with different P3HT layer thickness were measured and discussed. Efficiency improvements were observed in thinner P3HT layer thickness and with poly[3,4-(ethylenedioxy)-thiophene]:poly(styrene sulfonate) (PEDOT:PSS) as charge collection layer, and such device showed a short-circuit current density of 1.32 mA/cm², an open-circuit voltage of 0.44 V, a fill factor of 0.43, and a energy conversion efficiency of 0.25% at A.M. 1.5 solar illumination (100 mW/cm²).     

In2O3:Sn/TiO2/CdS heterojunction nanowire array photoanode in photoelectrochemical cells

The design of photoanode with highly efficient light harvesting and charge collection properties is important in photoelectrochemical (PEC) cell performance for hydrogen production. Here, we report the hierarchical In₂O₃:Sn/TiO₂/CdS heterojunction nanowire array photoanode (ITO/TiO₂/CdS-nanowire array photoanode) as it provides a short travel distance for charge carrier and long light absorption pathway by scattering effect. In addition, optical properties and device performance of the ITO/TiO₂/CdS-nanowire array photoanode were compared with the TiO₂ nanoparticle/CdS photoanode. The photocatalytic properties for water splitting were measured in the presence of sacrificial agent such as SO₃²⁻ and S²⁻ ions. Under illumination (AM 1.5G, 100 mW/cm²), ITO/TiO₂/CdS-nanowire array photoanode exhibits a photocurrent density of 8.36 mA/cm² at 0 V versus Ag/AgCl, which is four times higher than the TiO₂ nanoparticle/CdS photoanode. The maximum applied bias photon-to-current efficiency for the ITO/TiO₂/CdS-nanowire array and the TiO₂ nanoparticle/CdS photoanode were 3.33% and 2.09%, respectively. The improved light harvesting and the charge collection properties due to the increased light absorption pathway and reduced electron travel distance by ITO nanowire lead to enhancement of PEC performance.     

Solid-state photoelectrochemical cell using a polythiophene derivative as photoactive electrode

In this work, we investigated the photoelectrochemical behavior of poly(4,4′-dipentoxy-2,2′-bithiophene), poly(ET2), as a single electrode in a liquid electrolyte and also its use in a solid-state photoelectrochemical device using a polymeric electrolyte. The results showed a strong dependence of the photocurrent density on the type and concentration of the redox couple. The solid-state device exhibited a short-circuit current density of 4 μA cm⁻² and an open-circuit voltage of 9 mV. The maximum quantum yield of photocurrent in the visible range was 0.17%, high when compared to other photoelectrochemical devices based on organic materials; however, it is low in comparison to solid-state devices using inorganic materials. This paper shows the viability of using organic polymeric electrolytes in the construction of photoelectrochemical devices.     

Nanocomposite gel electrolyte with large enhanced charge transport properties of an I3/I redox couple for quasi-solid-state dye-sensitized solar cells

TiO₂ nanoparticles was introduced into quasi-solid-state Poly(vinylidenefluoride-co-hexafluoropropylene) (P(VDF-HFP)) based gel electrolyte to form nanocomposite gel electrolyte for quasi-solid-state dye-sensitized solar cells. The steady-state voltammograms revealed that the diffusion performance of the triiodide and iodide in the quasi-solid-state P(VDF-HFP) based gel electrolyte was greatly enhanced after the addition of TiO₂ nanoparticles. Especially, the apparent diffusion coefficient of I₃⁻ increased from 0.76×10⁻¹⁰ m²/s to 4.42×10⁻¹⁰ m²/s, reached the level of the liquid electrolyte (4.04×10⁻¹⁰ m²/s). By introducing TiO₂ nanoparticles, the photoelectric conversion efficiency of the gel based device increased from 5.72% to 7.18%, which reached the level of the liquid electrolytes based device (7.01%). The electrical impedance spectrum revealed that the addition of TiO₂ nanoparticles could reduce the charge recombination at the interface of dyed TiO₂ electrode/electrolyte. The results of the accelerated aging tests showed that the nano-TiO₂ composite gel electrolytes based devices could maintain 90% of their initial value after heating at 60 °C for 1000 h, which indicated that they had better thermostability than the corresponding normal gel electrolyte based devices and liquid electrolyte based devices.     

Preliminary photovoltaic response from a polymer containing p-vinylenephenylene amine backbone

Optoelectronic properties from a novel polymer, poly(p-phenylene N-4-n-butylphenyl-N,N-bis-4-vinylenephenylamine) (PNB) have been investigated. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the material were estimated to be −5.18 and −2.75 eV, respectively, measured with cyclic voltammetry. A single-layer device structure was prepared by spin-coating PNB thin films from a solution on top of an indium–tin oxide (ITO) substrate while aluminum was used as a top electrode. Current density–voltage (J–V) characteristic was measured which showed a typical rectifying behavior. Photovoltaic from a single-layered device was observed under a white arc lamp illumination. This was improved via a double-layer structure comprising vacuum evaporated copper phthalocyanine (CuPc) or N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C₁₃) as an additional layer. The open-circuit voltage, short-circuit current and hence the efficiency were improved in the double-layer devices. An ITO/PNB/PTCDI-C₁₃/Al device was estimated to have external quantum efficiency (EQE) around 1% at 330 nm. In a comparison of optical absorption and photocurrent spectra, it was demonstrated that the excitons could be separated and further, generated carriers drifting to the opposite electrodes more efficiently in the double-layer cells.     

Composition, surface topography, structure, Raman, and electrochemical/photoelectrochemical characterisation of CdxHg1−xTe films

Cd-rich Cd_xHg_{1 − x}Te films have been electrodeposited under potentiostatic conditions on conducting glass and Ti substrates from an acidic solution containing the respective ions as Cd²⁺:Hg²⁺:HTeO₂⁺ = 100:1:2. Six films one after another have been prepared from a single electrochemical cell. EDAX analysis of the air annealed films show decreasing Hg content in the deposit as the number of film preparation increases. SEM analysis indicate undulatory surface with Hg-rich clusters at the top surface. XRD analysis indicate the presence of Cd_xHg_{1 − x}Te along with . The Cd_xHg_{1 − x}Te alloy formation have been confirmed from Raman shift measurements which change with composition, x. The as-deposited films are n-type but converts to p-type after air annealing. Spectral response measurements gave band gap values that change with Hg content in the deposit. Band gap values ranging from 1.1 eV to 1.45 eV have been estimated. Photoelectrochemical solar cells using polysulphide electrolyte have been fabricated which gave an open-circuit photovoltage and short-circuit photocurrent, respectively, as 325 mV and 5.5 mA/cm² under 60 mW/cm² intensity of illumination.     

Effects of pH of a hybrid gel incorporated with 3-aminopropyltrimethoxysilane on the performance of a quasi-solid state dye-sensitized solar cell

Network hybrid gel prepared with tetraethyl orthosilicate, 3-aminopropyltrimethoxysilane (APS) and poly(ethylene glycol) was used as an electrolyte matrix in a quasi-solid state dye-sensitized solar cell (DSSC). Change in pH of this hybrid gel by varying the composition of APS was found to have remarkable effects on the photoelectrochemical performance of the cell. The hybrid gel matrix, having silane polymer backbones with free amine functionality, was characterized by FT-IR spectra and FE-SEM images, and the assembled DSSC by photocurrent-voltage and incident photon to current conversion efficiency curves. The unsealed, quasi-solid state DSSC with the hybrid gel has shown an increase in the open-circuit voltage (V_oc) and a steady decrease in the short-circuit photocurrent (J_sc), with increase in the content of APS. A maximum conversion efficiency of 4.5% was obtained for a DSSC by using 20% of APS in its hybrid gel at a light intensity of 100 mW cm⁻². Upon replacing the amino group of APS by bulkier aniline and benzophenoaniline groups, conversion efficiencies of the corresponding DSSCs were reduced. Variations in the V_oc and J_sc are explained in terms of shift of the flat band potential of TiO₂ and a complex formation between I₃⁻ and −NH₂ of APS of the electrolyte.     

Photoelectrochemical response and differential capacitance of poly(3-methylthiophene)

Following the theory used to study the semiconductor/electrolyte interface the differential capacitance of poly(3-methylthiophene) films has been determined from measurements with a lock-in amplifier and by electrochemical impedance spectroscopy (EIS). According to our findings, the best results were obtained by EIS because the space charge capacitance can be separated from the other capacitances. Using Mott–Schottky plots (C⁻² vs. E) we obtained the flat band potential E_fb=80 mV and the carrier density N=6×10¹⁷ cm⁻³ for the PMeT film in contact with the electrolyte, where dissolved O₂ played the role of the electron acceptor. The determined width of the depletion layer is 0.04 μm. We also investigated the photoelectrochemical response of the PMeT film. The plot of the square of the photocurrent vs. potential yields E_fb=90 mV, in good agreement with the EIS measurement. The dependence of the photocurrent with the frequency of the incident light shows that PMeT has a long response time (order of ms), compared to an inorganic semiconductor. The band gap was also determined from the photocurrent spectra. The value obtained, for a direct transition is 1.9 eV and is coincident with the value obtained from the absorption spectra.     

Au/Poly(3-methylthiophene)/10-(p-nitrobenzyl)-2(10H)-phenazinone/Al organic hetero-junction photovoltaic device

We proposed a novel concept of organic two-layer photovoltaic devices with D–σ–A molecule (Donor subunit–σ bond–Acceptor subunit)/conducting polymer heterojunction. Au/PMeT (poly(3-methylthiophene))/NBPN (10-(p-nitrobenzyl)-2(10H)-phenazinone)/Al was fabricated as a prototype of D–σ–A/polymer photovoltaic device. The power conversion efficiency of this photodiode was 5.1 × 10 ⁻²% under white illumination (8.46 mW/cm²). This value was larger than that of PMeT Schottky photodiode. This fact suggests that the concept of D–σ–A/polymer photovoltaic device is effective.     

Stable, easily sintered BaCe0.5Zr0.3Y0.16Zn0.04O3−δ electrolyte-based protonic ceramic membrane fuel cells with Ba0.5Sr0.5Zn0.2Fe0.8O3−δ perovskite cathode

A stable, easily sintered perovskite oxide BaCe_0.5Zr_0.3Y_0.16Zn_0.04O_3−δ (BCZYZn) as an electrolyte for protonic ceramic membrane fuel cells (PCMFCs) with Ba_0.5Sr_0.5Zn_0.2Fe_0.8O_3−δ (BSZF) perovskite cathode was investigated. The BCZYZn perovskite electrolyte synthesized by a modified Pechini method exhibited higher sinterability and reached 97.4% relative density at 1200 °C for 5 h in air, which is about 200 °C lower than that without Zn dopant. By fabricating thin membrane BCZYZn electrolyte (about 30 μm in thickness) on NiO–BCZYZn anode support, PCMFCs were assembled and tested by selecting stable BSZF perovskite cathode. An open-circuit potential of 1.00 V, a maximum power density of 236 mW cm⁻², and a low polarization resistance of the electrodes of 0.17 Ω cm² were achieved at 700 °C. This investigation indicated that proton conducting electrolyte BCZYZn with BSZF perovskite cathode is a promising material system for the next generation solid oxide fuel cells.     

Semiconductor-sensitized solar cells based on nanocrystalline In2S3/In2O3 thin film electrodes

A possibility of semiconductor-sensitized thin film solar cells have been proposed. Nanocrystalline In₂S₃-modified In₂O₃ electrodes were prepared with sulfidation of In₂O₃ thin film electrodes under H₂S atmosphere. The band gap (E_g) of In₂S₃ estimated from the onset of the absorption spectrum was approximately 2.0 eV. The photovoltaic properties of a photoelectrochemical solar cell based on In₂S₃/In₂O₃ thin film electrodes and I⁻/I₃⁻ redox electrolytes were investigated. This photoelectrochemical cell could convert visible light of 400–700 nm to electron. A highly efficient incident photon-to-electron conversion efficiency (IPCE) of 33% was obtained at 410 nm. The solar energy conversion efficiency, η, under AM 1.5 (100 mW cm⁻²) was 0.31% with a short-circuit photocurrent density (J_sc) of 3.10 mA cm⁻², a open-circuit photovoltage (V_oc) of 0.26 V, and a fill factor ( ff ) of 0.38.     

Investigation of influence of redox species on the interfacial energetics of a dye-sensitized nanoporous TiO2 solar cell

The photoelectrochemical behaviours of dye-sensitized nanoporous TiO₂ solar cells are studied under influences of light intensity, redox couple concentration, temperature, different cations and water in the nonaqueous solution. The value of the ideality factor of dyed nanoporous TiO₂ film is determined to be 1.08. The diode behaviour of the dyed nanoporous TiO₂ film approaches an ideal rectification characteristic. The rate of the reaction of I₃⁻ with the electron at the surface of the dyed TiO₂ electrode is of first order, like the reduction of I₃⁻ at the Pt electrode. By analysis of the relationship of the photovoltage with temperature, the activation energies of the back-reaction for dyed nanoporous TiO₂ electrodes in different solutions are obtained. Cations of different kinds and water are found to modify the interfacial properties of the dyed TiO₂ electrode. Finally, a quantitative relationship between the short-circuit photocurrent and the light intensity, the I₃⁻ concentration is obtained and used to explain the diffusion-controlled photocurrent. The corrected diffusion coefficient of I₃⁻ is 5.4–6.2×10⁻⁶ cm²/s in a CH₃OCH₂CN solution.     

Comparison of normal and inverse poly(3-hexylthiophene)/fullerene solar cell architectures

Polymer solar cells based on regioregular poly(3-hexylthiophene) (P3HT) and ([6,6]-phenyl-C61-butyric acid methyl ester) (PCBM) were fabricated with two different architectures (normal and inverse). Normal cells using indium tin oxide (ITO) as anode and Al as cathode were fabricated on polyester foils and illuminated from substrate side. Inverse cells using Ti as cathode and ultrathin Au layer as anode were illuminated from the top side covered by a transparent Au contact. Both Au layer and PET/ITO show comparable transmission in the spectral range where P3HT absorbs. Inverse cells showed comparable device parameters to normal cell (open circuit voltage 550 mV, short circuit current 6.25 mA/cm², fill factor 0.33 and white light power conversion efficiency 1.12%).