Monolithic Quasi-Solid-State Dye Sensitized Solar Cells Prepared Entirely by Printing Processes

A complete printing process was developed to fabricate the quasi-solid-state dye-sensitized solar cells with monolithic structures (m-QS-DSSCs). First, a structure of m-DSSCs was constructed by sequentially printing TiO2 layers (main and scattering), a ZrO2 insulating layer, and a carbon counter electrode (CE) onto an FTO substrate (FTO/TiO2/ZrO2/carbon CE). Then, a quasi-solid-state printable electrolyte (QS-PE), prepared using polyethylene oxide/polymethyl methacrylate, was printed directly on top of the porous carbon counter electrode (CE), enabling the m-QS-DSSCs to be prepared entirely by printing processes. In this study, the porous structures and characteristics of the ZrO2 and carbon layers were optimized by controlling the film thicknesses and heat treatment conditions; furthermore, the Pt layer was coated to improve the catalytic activity of carbon CEs. The results revealed that an appropriate porous structure of carbon and ZrO2 films could be obtained by heating the films from 200 to 500 °C. Through these porous layers, the QS-PE can penetrate well into the photoelectrodes, increasing the charge transport in the cells and at the electrode/electrolyte interfaces; therefore, the m-QS-DSSCs can achieve an efficiency of 6.79% under 1 sun illumination. Furthermore, the structures can also be utilized to fabricate liquid cells for application in a dim light environment. The m-QS-DSSCs remained stable during a long-term stability test at room temperature

Performance Enhancement of Quantum-Dot-Sensitized Solar Cells by Potential-Induced Ionic Layer Adsorption and Reaction

Successive ionic layer adsorption and reaction (SILAR) technique has been commonly adopted to fabricate quantum-dot-sensitized solar cells (QDSSCs) in the literature. However, pore blocking and poor distribution of quantum dots (QDs) in TiO₂ matrices were always encountered. Herein, we report an efficient method, termed as potential-induced ionic layer adsorption and reaction (PILAR), for in situ synthesizing and assembling CdSe QDs into mesoporous TiO₂ films. In the ion adsorption stage of this process, a negative bias was applied on the TiO₂ film to induce the adsorption of precursor ions. The experimental results show that this bias greatly enhanced the ion adsorption, accumulating a large amount of cadmium ions on the film surface for the following reaction with selenide precursors. Furthermore, this bias also drove cations deep into the bottom region of a TiO₂ film. These effects not only resulted in a higher deposited amount of CdSe, but also a more uniform distribution of the QDs along the TiO₂ film. By using the PILAR process, as well as the SILAR process to replenish the incorporated CdSe, an energy conversion efficiency of 4.30% can be achieved by the CdSe-sensitized solar cell. This performance is much higher than that of a cell prepared by the traditional SILAR process

Graphene Oxide Sponge as Nanofillers in Printable Electrolytes in High-Performance Quasi-Solid-State Dye-Sensitized Solar Cells

A graphene oxide sponge (GOS) is utilized for the first time as a nanofiller (NF) in printable electrolytes (PEs) based on poly­(ethylene oxide) and poly­(vinylidene fluoride) for quasi-solid-state dye-sensitized solar cells (QS-DSSCs). The effects of the various concentrations of GOS NFs on the ion diffusivity and conductivity of electrolytes and the performance of the QS-DSSCs are studied. The results show that the presence of GOS NFs significantly increases the diffusivity and conductivity of the PEs. The introduction of 1.5 wt % of GOS NFs decreases the charge-transfer resistance at the Pt-counter electrode/electrolyte interface (<i>R</i>_pt) and increases the recombination resistance at the photoelectrode/electrolyte interface (<i>R</i>_ct). QS-DSSC utilizing 1.5 wt % GOS NFs can achieve an energy conversion efficiency (8.78%) higher than that found for their liquid counterpart and other reported polymer gel electrolytes/GO NFs based DSSCs. The high energy conversion efficiency is a consequence of the increase in both the open-circuit potential (<i>V</i>_oc) and fill factor with a slight decrease in current density (<i>J</i>_sc). The cell efficiency can retain 86% of its initial value after a 500 h stability test at 60 °C under dark conditions. The long-term stability of the QS-DSSC with GOS NFs is higher than that without NFs. This result indicates that the GOS NFs do not cause dye-desorption from the photoanode in a long-term stability test, which infers a superior performance of GOS NFs as compared to TiO₂ NFs in terms of increasing the efficiency and long-term stability of QS-DSSCs

Electrodeposition of Copper on a Pt(111) Electrode in Sulfuric Acid Containing Poly(ethylene glycol) and Chloride Ions as Probed by in Situ STM

This study employed real-time in situ STM imaging to examine the adsorption of PEG molecules on Pt(111) modified by a monolayer of copper adatoms and the subsequent bulk Cu deposition in 1 M H₂SO₄ + 1 mM CuSO₄+ 1 mM KCl + 88 μM PEG. At the end of Cu underpotential deposition (∼0.35 V vs Ag/AgCl), a highly ordered Pt(111)-(√3 × √7)-Cu + HSO₄^– structure was observed in 1 M H₂SO₄ + 1 mM CuSO₄. This adlattice restructured upon the introduction of poly­(ethylene glycol) (PEG, molecular weight 200) and chloride anions. At the onset potential for bulk Cu deposition (∼0 V), a Pt(111)-(√3 × √3)­R30°-Cu + Cl^– structure was imaged with a tunneling current of 0.5 nA and a bias voltage of 100 mV. Lowering the tunneling current to 0.2 nA yielded a (4 × 4) structure, presumably because of adsorbed PEG200 molecules. The subsequent nucleation and deposition processes of Cu in solution containing PEG and Cl^– were examined, revealing the nucleation of 2- to 3-nm-wide CuCl clusters on an atomically smooth Pt(111) surface at overpotentials of less than 50 mV. With larger overpotential (η > 150 mV), Cu deposition seemed to bypass the production of CuCl species, leading to layered Cu deposition, starting preferentially at step defects, followed by lateral growth to cover the entire Pt electrode surface. These processes were observed with both PEG200 and 4000, although the former tended to produce more CuCl nanoclusters. Raising [H₂SO₄] to 1 M substantiates the suppressing effect of PEG on Cu deposition. This STM study provided atomic- or molecular-level insight into the effect of PEG additives on the deposition of Cu

Electrochemical Cu Growth on MPS-Modified Au(111) Electrodes

Au­(111) electrodes have been modified with self-assembled monolayers (SAM) of 3-mercapto-1-propanesulfonic acid (MPS) and used as a substrate for Cu electrodeposition. Aqueous plating solutions contained 0.1 M H₂SO₄, low Cu concentrations (≤80 μM), and, optionally, 1.4 mM Cl ions. The deposition process was characterized by cyclic voltammetry (CV) and in-situ scanning tunneling microscopy (STM) as a function of the electrode potential. At potentials positive of Cu growth (≥0.7 V_RHE), freshly modified electrodes are covered by an ordered (5√3 × √21) MPS adlayer (α) both in Cl-free and Cl-containing electrolytes. The α adlayer becomes disordered at more negative potentials prior to the onset of Cu deposition (≤0.65 V_RHE). In the potential regime of Cu underpotential deposition (UPD) (≈0.2–0.65 V_RHE), the surface morphology strongly depends on the presence of Cl. In the absence of Cl, a transient, ordered Cu/MPS adlayer phase (δ) forms via 2D growth and covers the entire Au(111) surface. Subsequently, the δ phase transforms into a disordered Cu/MPS phase (σ_Cu) with small, embedded Cu islands. In Cl-containing electrolyte, a disordered Cu/MPS/Cl phase (γ) nucleates at Au step edges or surface defects and spreads laterally. Cu islands form simultaneously within the γ phase. Two-dimensional growth of these islands results in a pure Cu-UPD layer. Overpotential deposition (OPD) proceeds via layer-by-layer mode with second layer nucleations at surprisingly small critical coverages (θ_C ≪ 0.5). Our observations differ significantly from those in previous studies, demonstrating that the Cu growth behavior critically depends on the concentrations of MPS, Cu, and Cl at the interface

Effects of TiO₂ and TiC Nanofillers on the Performance of Dye Sensitized Solar Cells Based on the Polymer Gel Electrolyte of a Cobalt Redox System

Polymer gel electrolytes (PGEs) of cobalt redox system are prepared for dye sensitized solar cell (DSSC) applications. Poly­(vinylidene fluoride-<i>co</i>-hexafluoropropylene) (PVDF-HFP) is used as a gelator of an acetonitrile (ACN) liquid electrolyte containing tris­(2,2′-bipyridine)­cobalt­(II/III) redox couple. Titanium dioxide (TiO₂) and titanium carbide (TiC) nanoparticles are utilized as nanofillers (NFs) of this PGE, and the effects of the two NFs on the conductivity of the PGEs, charge-transfer resistances at the electrode/PGE interface, and the performance of the gel-state DSSCs are studied and compared. The results show that the presence of TiC NFs significantly increases the conductivity of the PGE and decreases the charge-transfer resistance at the Pt counter-electrode (CE)/PGE interface. Therefore, the gel-state DSSC utilizing TiC NFs can achieve a conversion efficiency (6.29%) comparable to its liquid counterpart (6.30%), and, furthermore, the cell efficiency can retain 94% of its initial value after a 1000 h stability test at 50 °C. On the contrary, introduction of TiO₂ NFs in the PGE causes a decrease of cell performances. It shows that the presence of TiO₂ NFs increases the charge-transfer resistance at the Pt CE/PGE interface, induces the charge recombination at the photoanode/PGE interface, and, furthermore, causes a dye desorption in a long-term-stability test. These results are different from those reported for the iodide redox system and are ascribed to a specific attractive interaction between TiO₂ and cobalt redox ions

Charge Transfer in the Heterointerfaces of CdS/CdSe Cosensitized TiO₂ Photoelectrode

One of the key issues affecting the performance of solar cells is the behavior of carrier transfer. In this work, the time-resolved photoluminescence (TRPL) technique was utilized to investigate the electron transfer at the CdS/CdSe, TiO₂/CdS, and TiO₂/CdSe heterointerfaces. By varying the excitation wavelengths, photoluminescence lifetimes of CdSe and CdS in TiO₂/CdSe, TiO₂/CdS, TiO₂/CdS/CdSe, and TiO₂/CdSe/CdS photoelectrodes were measured. The results show that, for the single sensitizer electrodes (TiO₂/CdS, TiO₂/CdSe), the average PL lifetime of CdS (0.69 ns) is shorter than CdSe (0.99 ns), suggesting that CdS has higher electron transfer rate toward TiO₂ compared with CdSe. For the TiO₂/CdSe/CdS electrode, the PL lifetime of CdSe exhibits an excitation-wavelength-dependent behavior. A shorter excitation wavelength leads to a longer PL lifetime of CdSe. This additional long lifetime is ascribed to the rapid carrier transfer from the photoexcited carriers in CdS layer into the CdSe layer. On the contrary, the PL lifetime of CdSe is independent of the excitation wavelength in the TiO₂/CdS/CdSe electrode, indicating that the excited electrons in the CdS layer did not inject into the CdSe layer. This observation confirms that the charge transfer from the cosensitizers toward the TiO₂ is much more efficient in the TiO₂/CdS/CdSe electrode rather than in the TiO₂/CdSe/CdS electrode

Immobilization of Anions on Polymer Matrices for Gel Electrolytes with High Conductivity and Stability in Lithium Ion Batteries

This study reports on a high ionic-conductivity gel polymer electrolyte (GPE), which is supported by a TiO₂ nanoparticle-decorated polymer framework comprising poly­(acrylonitrile-<i>co</i>-vinyl acetate) blended with poly­(methyl methacrylate), i.e., PAVM:TiO₂. High conductivity GPE-PAVM:TiO₂ is achieved by causing the PAVM:TiO₂ polymer framework to swell in 1 M LiPF₆ in carbonate solvent. Raman analysis results demonstrate that the poly­(acrylonitrile) (PAN) segments and TiO₂ nanoparticles strongly adsorb PF₆^– anions, thereby generating 3D percolative space-charge pathways surrounding the polymer framework for Li⁺-ion transport. The ionic conductivity of GPE-PAVM:TiO₂ is nearly 1 order of magnitude higher than that of commercial separator-supported liquid electrolyte (SLE). GPE-PAVM:TiO₂ has a high Li⁺ transference number (0.7), indicating that most of the PF₆^– anions are stationary, which suppresses PF₆^– decomposition and substantially enlarges the voltage that can be applied to GPE-PAVM:TiO₂ (to 6.5 V vs Li/Li⁺). Immobilization of PF₆^– anions also leads to the formation of stable solid-electrolyte interface (SEI) layers in a full-cell graphite|electrolyte|LiFePO₄ battery, which exhibits low SEI and overall resistances. The graphite|electrolyte|LiFePO₄ battery delivers high capacity of 84 mAh g^–1 even at 20 C and presents 90% and 71% capacity retention after 100 and 1000 charge–discharge cycles, respectively. This study demonstrates a GPE architecture comprising 3D space charge pathways for Li⁺ ions and suppresses anion decomposition to improve the stability and lifespan of the resulting LIBs