Lithium ion-conducting polymer electrolytes based on PVA–PAN doped with lithium triflate

Ionics - Blend polymer electrolytes with optimized composition (92.5 PVA:7.5 PAN) doped with lithium triflate (LiCF3SO3) have been prepared in different concentrations by solution casting...     

Simulation design of P–I–N-type all-perovskite solar cells with high efficiency

According to the good charge transporting property of perovskite, we design and simulate a p–i–n-type all-perovskite solar cell by using one-dimensional device simulator. The perovskite charge transporting layers and the perovskite absorber constitute the all-perovskite cell. By modulating the cell parameters, such as layer thickness values, doping concentrations and energy bands of n-, i-, and p-type perovskite layers, the all-perovskite solar cell obtains a high power conversion efficiency of 25.84%. The band matched cell shows appreciably improved performance with widen absorption spectrum and lowered recombination rate, so weobtain a high J_(sc) of 32.47 m A/cm~2. The small series resistance of the all-perovskite solar cell also benefits the high J_(sc). The simulation provides a novel thought of designing perovskite solar cells with simple producing process, low production cost and high efficient structure to solve the energy problem.     

Synthesis of self-light-scattering wrinkle structured ZnO photoanode by sol–gel method for dye-sensitized solar cells

A special morphological zinc oxide (ZnO) photoanode for dye-sensitized solar cell was fabricated by simple sol–gel drop casting technique. This film shows a wrinkled structure resembling the roots of banyan tree, which acts as an effective self scattering layer for harvesting more visible light and offers an easy transport path for photo-injected electrons. These ZnO electrode of low thickness (~5 μm) gained an enhanced short-circuit current density of 6.15 mA/cm², open-circuit voltage of 0.67 V, fill factor of 0.47 and overall conversion efficiency of 1.97 % under 1 sun illumination. This shows a high conversion efficiency and a superior performance than that of ZnO nanoparticle-based photoanode (η ~ 1.13 %) of high thickness (~8 μm).     

Improved efficiency of dye-sensitized solar cells applied with nanostructured N–F doped TiO2 electrode

Dye-sensitized solar cells (DSSCs) were fabricated with N–F-doped TiO₂ electrodes. The XRD pattern of the N–F-doped TiO₂ is almost the same as that of pure TiO₂, showing that N and F doping has little influence on the formation of anatase titania. The influence of dopant N and F on band energetics and photoelectrochemical properties of nanostructured TiO₂ electrodes were investigated. Compared with pure TiO₂ electrodes, the E_fb of N–F-doped TiO₂ electrodes shifted a little in electrolytes containing LiClO₄. However the total trap densities were remarkably decreased as TiO₂ electrodes were doped with N and F. Finally the N–F-doped TiO₂ electrodes were sensitized with N3 and their photoelectrochemical properties were studied. Experimental results showed that the photoelectric conversion efficiency of N3 sensitized N–F-doped TiO₂ electrodes was 8.61% under irradiation of 100 mW cm^?2 white light, about 17.1% higher than that of a pure TiO₂ electrode.     

Efficiency enhancement of flexible dye-sensitized solar cell with sol–gel formed Nb2O5 blocking layer

We investigated the effect of a Nb₂O₅ blocking layer formed through the sol–gel method introduced to a titanium metal foil electrode in a flexible dye sensitized solar cell. The blocking layer formed directly on the working electrode physically separates the working electrode from the electrolyte, and prevents back transfer of electrons from the electrode to the electrolyte. The gel processing conditions (sol reaction time) and heat treatment temperature used in formation of the Nb₂O₅ blocking layer have been shown to affect the performance of the dye sensitized solar cell and optimal values of these parameters have been determined. A sol reaction time of 45 min and heat treatment temperature of 550 °C has been observed to result in optimal cell performance (η = 6.185%, J_sc = 13.233 mA/cm², V_oc = 0.672 V, ff = 0.694). Introduction of an Nb₂O₅ blocking layer enhances solar cell efficiency by 39.7%, which is much greater than the increase of 24.6% observed in a similar cell containing a TiO₂ blocking layer under standard illumination conditions. The results obtained via Nb₂O₅ have been observed to be superior to those obtained via a TiO₂ blocking layer.     

Characteraction of Ag-doped ZnO thin film synthesized by sol–gel method and its using in thin film solar cells

Pure 2% and 4% Ag-doped ZnO thin films have been synthesized on glass substrates by sol–gel method. The structure, morphology and optical properties of the samples have been studied by X-ray diffractometer (XRD), scanning probe microscope, UV–vis spectrophotometer, respectively. The XRD result shows that the pure ZnO has a wurtzite hexagonal structure, no phase segregation is observed. The surface morphology of pure ZnO thin film shows that the grains are growing preferentially along the c-axis orientation perpendicular to the substrates. The transmittance spectra reveal that all samples have high transmittance above 90% in visible region. With Ag doping content increase, a red shift is observed. The performance of Ag-doped ZnO films using in thin film solar cells are simulated. The results show that 4% Ag-doped ZnO thin film can greatly improve the absorption of the cells. Compare to pure ZnO, solar cell's energy conversion efficiency improvement of 2.47% is obtained with 4% Ag doped ZnO thin film.     

Effects of annealing rate and morphology of sol–gel derived ZnO on the performance of inverted polymer solar cells

The effects of annealing rate and morphology of sol–gel derived zinc oxide(ZnO)thin films on the performance of inverted polymer solar cells(IPSCs)are investigated.ZnO films with different morphologies are prepared at different annealing rates and used as the electron transport layers in IPSCs.The undulating morphologies of ZnO films fabricated at annealing rates of 10 C/min and 3 C/min each possess a rougher surface than that of the ZnO film fabricated at a fast annealing rate of 50 C/min.The ZnO films are characterized by atomic force microscopy(AFM),optical transmittance measurements,and simulation.The results indicate that the ZnO film formed at 3 C/min possesses a good-quality contact area with the active layer.Combined with a moderate light-scattering,the resulting device shows a 16%improvement in power conversion efficiency compared with that of the rapidly annealed ZnO film device.     

Conduction mechanism of lithium bis(oxalato)borate–cellulose acetate polymer gel electrolytes

Polymer gel electrolytes (PGE) belonging to salt–solvent–polymer hybrid systems are prepared using a mixture of lithium bis(oxalato)borate (LiBOB), γ-butyrolactone (γ-BL), and cellulose acetate (CA). The increase in ionic conductivity of PGE is due to the dissociation of ion aggregates, as confirmed by Fourier transform infrared analysis. The highest conductivity attained by the PGE is 7.05 mS cm^?1 at 2.4 wt.% CA. The plots of conductivity–temperature show a classical Arrhenius relationship. The electrical properties of the sample with the highest conductivity are analyzed using electrical permittivity and electric modulus formalism studies. Meanwhile, the frequency-dependent conductivity of the polymer gel electrolyte adheres to Jonscher’s power law. Conduction mechanism study also shows that the 2.4 wt.% CA PGE is in agreement with the small polaron hopping model.     

Numerical simulation of solar cells based on III–V nitride compounds

In this paper, we developed a numerical calculation program, using Turbo Pascal, to determine the current–voltage characteristics of a $\hbox {N}^{+}\hbox {P}$ solar cells in order to find the main parameters influencing the conversion efficiency. We adopted a one-dimensional numerical model for the resolution of the three semiconductor equations, which are: the Poisson’s equation and the two continuity equations of electrons and holes. Our system of equations is written in term of $\varphi ,\, \varphi _{n}$ , and $\varphi _{p}$ , and it’s resolved using the finite difference method. This code enables us to draw the current density versus the voltage for different layer thicknesses, the conversion efficiency versus the minority carrier life time and the spectral response versus the wavelength. In order to compare the conversion efficiency of two different solar cells, we simulated a solar cell based on III–V nitride compounds $(\hbox {In}_\mathrm{x}\hbox {Ga}_{1-\mathrm{x}}\hbox {N})$ and a monocrystalline silicon solar cell.     

Carrier transport in III–V quantum-dot structures for solar cells or photodetectors

According to the well-established light-to-electricity conversion theory,resonant excited carriers in the quantum dots will relax to the ground states and cannot escape from the quantum dots to form photocurrent,which have been observed in quantum dots without a p–n junction at an external bias.Here,we experimentally observed more than 88% of the resonantly excited photo carriers escaping from In As quantum dots embedded in a short-circuited p–n junction to form photocurrent.The phenomenon cannot be explained by thermionic emission,tunneling process,and intermediate-band theories.A new mechanism is suggested that the photo carriers escape directly from the quantum dots to form photocurrent rather than relax to the ground state of quantum dots induced by a p–n junction.The finding is important for understanding the low-dimensional semiconductor physics and applications in solar cells and photodiode detectors.     

Poly ethylene oxide (PEO)–LiI polymer electrolytes embedded with CdO nanoparticles

Improvement of electrical conductivity of poly ethylene oxide (PEO)–LiI polymer electrolytes is necessary for their use in solid state lithium ion battery. In this study a new kind of PEO–LiI-based polymer electrolytes embedded with CdO nanoparticles with improved electrical conductivity has been prepared and characterized. The electron microscopic studies confirm that CdO nanoparticles of average size 2.5 nm are dispersed in the PEO matrix. The glass transition temperature of the PEO–LiI electrolyte decreases with the introduction of CdO nanoparticle in the polymer matrix. X-ray diffraction, electron microscopic, and differential scanning calorimetry studies show that the amorphous phase of PEO increases with the introduction of CdO nanoparticle and that the increase in amorphous phase is maximum for 0.10 wt% CdO doping. The electrical conductivity of the sample with 0.10 wt% CdO increases by three orders in magnitude than that of the PEO–LiI electrolyte. The electrical conductivity of PEO–LiI electrolyte embedded with CdO nanoparticle exhibits VTF behavior with reciprocal temperature indicating a strong coupling between the ionic and the polymer chain segmental motions.     

Fabrication of Fe:CdSe solar rechargeable (semiconductor–septum) storage cells

The Fe:CdSe thin films have been electrodeposited potentiostatically onto the stainless steel substrates, from non-aqueous bath containing (CH₃COO)₂ · Cd · 2H₂O, SeO₂ and FeCl₃. The solar rechargeable (semiconductor–septum) storage cell is fabricated with the configuration C|1 M polysulphide|n-Fe:CdSe|stainless steel||1 M FeCl₃ or 1 M K₄Fe(CN)₆|C. The charging and discharging modes are studied and discussed. The comparison of FeCl₃ and K₄Fe(CN)₆ based solar rechargeable storage cells, showed that FeCl₃ based storage cell is superior than that of K₄Fe(CN)₆ based electrolyte because relatively charging time is minimum and discharging time is maximum. Thus it is concluded that the storage cell works not only as a generator but also as the storage of electricity.     

Multistep spin–spray deposition of large-grain-size CH3NH3PbI3 with bilayer structure for conductive-carbon-based perovskite solar cells

Large-grain-size and void-free CH₃NH₃PbI₃ films with bilayer structure are fabricated by spin-coating a PbI₂ layer onto a mesoporous TiO₂ layer and sequentially spraying CH₃NH₃I (methylammonium iodide, MAI) multilayers. The sprayer is controlled by a homemade three-axis computer numerical control machine; thus, the substrates are coated by successive parallel passes achieved by moving the nozzle. Spray deposition at the optimal spray rate and substrate temperature produces a large-grain-size and void-free methylammonium lead iodide (MAPbI₃) bilayer structure. The mesoporous TiO₂ layer plays an important role in electron transport by preventing the return of electrons to the perovskite layer and decreasing the contact resistance at the perovskite/compact TiO₂/fluorine tin oxide interface. When the films are incorporated into a solar cell device with a conductive carbon counter electrode, a maximum power conversion efficiency of 10.58% is realised.     

Dye-sensitized solar cells with 3D flower-like α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-decorated reduced graphenes oxide as photoanodes

For the first time, we report a one-step fabrication of an environment-friendly approach to synthesize flower-like α-Fe₂O₃ hierarchical nanoparticles (NPs)/reduced graphene oxide (RGO) hybrids by combining the graphene oxide (GO) with the growth of α-Fe₂O₃ NPs. The GO sheet which possesses the functional group, such as hydroxyl (–OH) and carbonyl groups (–OOH), can be easily incorporated with the petal of the flower-like α-Fe₂O₃ in ethanol and water solution through a solvothermal process, during which GO is reduced to RGO without the addition of any strong reducing agent or requiring any post-high-temperature annealing process. The as-prepared samples are loose and porous with flower-like structure, and the RGO hybrids were wrapped up uniformly on the sheet of α-Fe₂O₃ NPs. To demonstrate the potential applications, we have fabricated dye-sensitized solar cells (DSSCs) from the as-synthesized hierarchical flower-like α-Fe₂O₃/RGO and investigated it for the photoanode of DSSCs. Results show that the hierarchical α-Fe₂O₃/RGO solar cell exhibits improved performances in comparison with the free α-Fe₂O₃ NPs. The enhancement of photovoltaic properties is attributed to the unique porous nature and good conductivity which allow more efficient diffusion of I^? ions and facilitate the transfer of electron in the network.     

New type of inorganic–organic hybrid (heteropolytungsticacid–polyepichlorohydrin) polymer electrolyte with TiO2 nanofiller for solid state dye sensitized solar cells

A new type of inorganic–organic hybrid solid state polymer electrolyte consisting of heteropolytungsticacid impregnated polyepichlorohydrin with iodine/iodide and TiO₂ nanofiller have been prepared for their potential application in dye sensitized solar cells. The prepared polymer electrolytes were well characterized by FT-IR, Scanning electron microscopy (SEM), X-ray diffraction (XRD), Electrochemical Impedance analysis (EIS) and Thermal analysis (TGA). The prepared polymer electrolyte with TiO₂ nanofiller shows reasonable ionic conductivity (20.4 × 10⁻⁶ S cm⁻¹) compared to pure polyepichlorohydrin (2.0 × 10⁻⁹ S cm⁻¹) at ambient temperature. The presence of negatively charged redox species heteropolytungsticacid in the polymer matrix prevents the photo reduction of iodide (back electron transfer) and the presence of TiO₂ nanofiller increases the degree of amorphousity of the polymer which in turn prolongs the stability of the fabricated dye sensitized solar cell over a long period compared to bare polymer electrolyte.     

Correlation of band electronic structure with efficiency in perovskite solar cells with vanadium (Ⅳ) oxide thin film buffers

Perovskite solar cells have been studied extensively in the area of perovskite solar cells because they have a comparatively free hysteresis. Through fabrication of a perovskite solar cell based on a vanadium oxide buffer, this study clarified the mechanism of electron and hole transport in the laminated layer upon irradiation with light. The power conversion efficiency (PCE) of the Vanadium (Ⅳ) oxide (VO₂) sputtering process device was approximately 13% and with the spin-coating process was 8.5%. To investigate the physicochemical origin of such PCE differences depending on the process type, comprehensive band alignment and band structure analyses of the actual cell stacks were performed using X-ray photoelectron spectroscopy depth measurements. Accordingly, it was found that the inconsistent valence band offset between the perovskite absorption layer and V₂O₅ layer as a function of the VO₂ process type caused a difference in the hole transport, resulting in the difference in the efficiency.     

Enhanced efficiency of dye-sensitized solar cells by UV–O3 treatment of TiO2 layer

Solar conversion efficiency of dye-sensitized solar cells was improved by UV–O₃ treatment of TiO₂ before and/or after sintering. The enhancement was resulted from the removal of the residual organics originated from the TiO₂ precursor pastes, increased adsorption of dyes to the TiO₂, surface, and longer diffusion length and shorter electron transit time of electrons through the TiO₂ mesoscopic structure. The power conversion efficiency of the cells reaches to 7.2% with the open circuit voltage of 0.71 V, the short circuit current density of 15.2 mA/cm² and the fill factor of 0.67 under illumination with AM 1.5 (100 mW/cm²) simulated sunlight.