TiO2 Compact Layer Research Articles

Solar Cells Constructed with Polythiophene Thin Films Grown along Tethered Thiophene-Dye Conjugates via Photoelectrochemical Polymerization.

A polythiophene-based solar cell (PTSC) is constructed by photoelectrochemically polymerizing thiophene onto an ultrathin compact TiO2 layer (150 nm thick) covered with a sub-monolayer of tethered 3-{5-[ N, N-bis(4-diphenylamino)phenyl]thieno[3,2- b]thiophen-2-yl}-2-cyano-acrylic acid dye (ca. 10% coverage). The influence of morphology and thickness of the PT film on the photocurrent generated by the PTSC was investigated. With a 270 nm thick PT film and 2,2',7,7'-tetrakis( N, N-di(4-methoxyphenyl)amino)-9,9'-spirobifluorene serving as the hole-transport material, the PTSC exhibited a short-circuit current density JSC of 12.90 ± 0.63 mA/cm2, an open-circuit voltage VOC of 0.81 ± 0.01 V, and a fill factor of 0.72 ± 0.01. The high conversion efficiency (7.52 ± 0.58%) of the PTSC is attributed to the controlled PT growth along the ordered and spatially accessible dye molecules at the compact TiO2 layer, which facilitates charge transfer, prevents the hole/electron recombination, and simplifies the polymer solar cell construction with a stable and easily processable material.

Yttrium-doped TiO2 compact layers for efficient perovskite solar cells

To improve the electron transporting and suppress the charge recombination at the interface of TiO2/perovskite, the smooth and compact yttrium(Y)-doped TiO2 compact layers were successfully prepared via a hydrolysis-pyrolysis method. The influences of Y-doped on the microstructure, crystal phase, chemical composition, optical absorption of the TiO2 compact layers were investigated, and the electron transporting and charge recombination at the TiO2/perovskite interface of solar cells were systemically analyzed. The planar perovskite solar cells based on the Y-doped TiO2 compact layers with a Y/Ti molar ratio of 5% obtained a best photoelectric conversion efficiency (PCE) of 15.52%, comparing with a PCE of 14.05% from the undoped devices. When the 200-nm length 3% Y-doped TiO2 nanorod arrays were introduced between the 5% Y-doped TiO2 compact layers and the perovskite thin film, the champion cell achieved a PCE of 18.32% under illumination of simulated AM 1.5 sunlight (100 mA cm−2).

Multi-dimensional anatase TiO2 materials: Synthesis and their application as efficient charge transporter in perovskite solar cells

Recently, organo-metal halide perovskite (e.g., CH3NH3PbI3) solar cells have shown a significant surge in progress and efficiency. The photovoltaic performance of perovskite solar cells (PSC) extensively depends on the morphology of the materials at nano-level, because the intrinsic electrical, optical and electrochemical properties also change with a change in morphology. Different TiO2 nanostructures with diverse dimensionalities, 0D hollow TiO2 nanoparticles (HTNPs), 3D hollow TiO2 mesospheres (HTMSs) and 3D hierarchical TiO2 spheres (HTSs) were synthesized hydrothermally. The PSCs based on 3D HTSs or 3D HTMSs as electron transport layers (ETLs) shows better performance than the PSCs fabricated with 0D HTNPs as ETL. The enhanced results can be attributed to the better penetration of the perovskite materials in the porous network of the HTSs or HTMSs and decreased interfacial recombination due to superior charge extraction and electron transport at the HTSs/CH3NH3PbI or HTMSs/CH3NH3Pb interfaces. By using a self-assembled TiO2 compact layer (c-TiO2), followed by a mesoporous layer of HTSs, produces PSCs with an excellent efficiency of 15.08%. Such c-TiO2-ETL films may improve PSCs performance by enhancing electron extraction and block the photogenerated holes.

The effect of nitrogen doping of TiO2 compact blocking layers on perovskite solar cell performance

In this paper, nitrogen-doped titanium oxide (N-TiO2) with different dopant concentrations (0, 0.25, 0.5, and 1 at.%) were grown on FTO substrates by spray pyrolysis and applied in perovskite solar cells (PVSC) as a compact blocking layer. Morphology, chemical and physical properties of the samples were investigated by SEM, XRD, XPS, UV–Visible, and PL characterization techniques. Measurements indicate that the device based on N-TiO2 with a nitrogen content of 0.25% exhibits higher PCE (17.83%) than the device based on un-doped TiO2 (17.04%). Results show that the lowest series resistance is obtained in the device based on 0.25% N-TiO2, leading to an increase in the fill factor (FF) parameter. Also, higher VOC of this device results from lower e-h recombination due to longer electron lifetime than the un-doped sample. In addition, a slight increase in JSC is related to the small decrease in the band gap of TiO2 with nitrogen doping. Enhanced FF, VOC, and JSC are the main reasons for the improved performance of the PVSC devices by using the optimal level of nitrogen in TiO2.

New Strategy to Overcome the Instability That Could Speed up the Commercialization of Perovskite Solar Cells

AbstractCurrent efficiency of perovskite solar cells has reached 23.7%, which is comparable with silicon solar cells. However commercial development is seriously hindered by the instability of the perovskite, especially under moisture conditions. Therefore it is crucial to gain clear understanding of the mechanism of degradation of organic–inorganic perovskite in order to achieve stable perovskite devices. In this paper, the formation and the degradation of perovskite film on different charge transport layers such as a compact TiO2 layer, compact ZnO layer, and ZnO foil, Si nanowires, and porous Si are studied. In addition, density functional theory studies are carried out to better understand the interaction between the perovskite film and substrates. Experimental and theoretical results are combined to draw more reliable conclusion regarding the degradation mechanism. Most notably, the investigations show that the interaction between the iodine (I) atom in the perovskite layer and substrate determine the stability of perovskite cells. As a result, Si has minimum interaction with I atoms and shows maximum stability, while perovskite film degrades on TiO2 film almost immediately.

Enhanced morphology and photoelectric properties of one-dimensional TiO2 nanorod array films

Abstract One-dimensional TiO2 nanorod array films (1D TNA films) were prepared by the two-step process. The results show that the density of 1D TNA films is significantly improved with the presence of TiO2 compact layer (TCL) and the hydrothermal reaction time of 15 h. The TiO2 crystallinity is improved. The utilization efficiency of the visible light is increased with the lower concentration of crystal defects. The charge recombination center caused by the defects decreased, while the electrons and holes were effectively separated, thus the charge recombination rate was lowered, and better charge transport performance caused the transient photocurrent to increase significantly.

Performance of Perovskite Solar Cell Using Compact Layer by Sputter Deposition

A uniform compact layer is essential for obtaining high-efficiency perovskite solar cells (PSCs). This is because direct contact between the FTO glass substrate and the perovskite layer should be blocked to suppress electron recombination and to collect electrons. In the present study, PSCs were fabricated using sputtered TiO₂ compact layers prepared at different deposition times. The structure, morphology, and electrical properties of the sputter deposited TiO₂ compact layer were compared to those of a spin coated TiO₂ film. The TiO₂ compact layer prepared by the sputtering process was very smooth and inhibited electron recombination at the FTO interface, resulting in a higher open circuit voltage and a higher short circuit current density. A photoelectric conversion efficiency of 13.37% was obtained using the TiO₂ compact layer deposited for 30 min.

Comprehensive understanding of TiCl4 treatment on the compact TiO2 layer in planar perovskite solar cells with efficiencies over 20%

A uniform and compact hole blocking layer is necessary for high-performance perovskite solar cells, since it not only serves as an electron collector but also suppresses the carrier recombination. So far, high efficient perovskite solar cells have been obtained by using a blocking layer TiO2 that requires an additional TiCl4 treatment. In this paper, a comprehensive understanding of TiCl4 treatment on the TiO2 layer was investigated in planar perovskite solar cells. Scanning electron microscope, atomic force microscope, and Kelvin probe force microscopy were applied to investigate the morphology of the TiCl4 treated TiO2, and steady-state photo luminescence spectroscopy and electrical impedance spectroscopy were conducted to study charge carrier dynamics. The TiCl4 treated TiO2 layer can result in high efficiency over 20% in planar perovskite solar cells. Our results demonstrate that the TiCl4 treatment on the compact TiO2 prior to the perovskite deposition was necessary for achieving high-performance solar cells.

Improving the performance of inverted polymer solar cells through modification of compact TiO2 layer by different boronic acid functionalized self-assembled monolayers

In this study, we demonstrate the use of a series of boronic acid functionalized self-assembled monolayers (SAMs) to improve photovoltaic device performance P3HT and PCBM based solar cells. The SAMs treated compact TiO2 (c-TiO2) layer was utilized as an electron transport layer for inverted polymer solar cells (PSCs) with a configuration of FTO/c-TiO2/SAM/P3HT:PCBM/PEDOT:PSS/Ag. The modified with 3,4,5-methoxyphenylboronic acid (3-OMe) SAM shows the best improving due to the enhancement of Jsc and Voc in device, which leads to a 26% improvement (2.8%) over non-modified device (2.2%). The enhancement in the modified devices is achieved by SAM modification reducing recombination of charges and improving charge selectivity. These results prove that the surface and electrical properties of compact TiO2 (c-TiO2) layer can be easily tuned as well as the upper layer morphology can be controlled by SAM modification.

Mass Manufactured Glass Substrates Incorporating Prefabricated Electron Transport Layers for Perovskite Solar Cells

AbstractA commercially available glass substrate which incorporates both a fluorine‐doped tin oxide and compact TiO2 layer deposited through chemical vapor deposition that is commonly used in “solar control products,” is presented. The substrate, known commercially as Pilkington Eclipse Advantage, is designed for use as an infrared radiation control product and this is the first known instance of it being employed and extensively characterized for use as a mass manufactured n‐type contact in perovskite solar cells. Using this substrate with no additional compact TiO2 layer, perovskite solar cells with PCEs of up to 15.9% are achieved. These devices are superior in performance to those where the compact TiO2 is deposited via spray pyrolysis. The reproducibility and large scale manufacturing base already established with this substrate represents significant potential for solving the problem of upscaling a uniform and pinhole free n‐type compact TiO2 blocking layer.

Highly Compact TiO2 Films by Spray Pyrolysis and Application in Perovskite Solar Cells

Transparent and pinhole free hole‐blocking layers such as TiO2 grown at low temperatures and by scalable processes are necessary to reduce production costs and thus enabling commercialization of perovskite solar cells. Here, the authors compare the transport properties of TiO2 compact layers grown by spray pyrolysis from commonly used titanium diisopropoxide bisacetylacetonate ([Ti(OPri)2(acac)2]) precursor to films grown by spray pyrolysis of TiCl4. Spray pyrolysis provides insights into the interdependence of precursor chemistry and electron transport properties of TiO2 films and their influence on the performance of the perovskite solar cells. X‐ray diffraction and X‐ray photoelectron spectroscopy data confirm the chemical and structural composition of the obtained films. Thin film deposition at lower temperature (150 °C) are conducted using TiCl4 to evaluate the influence of crystal growth and topography by scanning electron microscopy and atomic force microscopy as well as thickness (profilometry) and transmittance (UV/Vis spectroscopy) on the power conversion efficiency of perovskite solar cells. TiO2 compact layers grown from TiCl4 enhance the power conversion efficiency by acting as superior electron transfer medium and by reducing hysteresis behavior, when compared to films grown using titanium diisopropoxide bisacetylacetonate. UV/Vis spectroscopy and external quantum efficiency studies reveal the correlation of transmittance on the power conversion efficiency.

Fabrication and Electrochemical Impedance Analysis of Dye-Sensitized Solar Cells With Titanium Dioxide Compact Layer and Graphene Oxide Dye Absorption Layer

Two different structures of titanium dioxide (TiO2) photoelectrode were fabricated to test for possible improvements in the photovoltaic properties of dye-sensitized solar cells (DSSCs). In the first layer, a TiO2 compact layer was deposited by radio frequency sputtering. It was able to transmit abundantly and showed excellent electron transport. The second layer of TiO2 photoelectrode was the dye absorption layer, which was composed of TiO2+graphene oxide (GO). The high specific surface area of GO increased the adsorption of dye molecules. The photovoltaic conversion efficiency (η), charge transport properties of the DSSC with a compact layer and a dye absorption layer were measured using electrochemical impedance spectroscopy. Experiment results showed η of the DSSC with a compact layer and a dye absorption layer achieved 3.15% because the electron transportation of DSSC had been enhanced by a compact layer and a dye absorption layer.

Blocking the Charge Recombination with Diiodide Radicals by TiO2 Compact Layer in Dye-Sensitized Solar Cells

The addition of a compact titanium dioxide (TiO2) layer between the fluorine-doped tin oxide (FTO) coated glass substrate and the mesoporous TiO2 layer in the dye-sensitized solar cell (DSC) based on the iodide/triiodide redox couple (I−/I3−) is known to improve its current-voltage characteristics. The compact layer decreases the recombination of electrons extracted through the FTO layer with I3− around the maximum power point. Furthermore, the short-circuit photocurrent was improved, which previously has been attributed to the improved light transmittance and/or better contact between TiO2 and FTO. Here, we demonstrate that the compact TiO2 layer has another beneficial effect: it blocks the reaction between charge carriers in the FTO and photogenerated diiodide radical species (I2−•). Using photomodulated voltammetry, it is demonstrated that the cathodic photocurrent found at bare FTO electrodes is blocked by the addition of a compact TiO2 layer, while the anodic photocurrent due to reaction with I2−• is maintained.

Hydrothermal growth of well-aligned TiO2 nanorods on fluorine-doped tin oxide glass

Abstract One-dimensional titanium dioxide nanostructures have been studied intensively and extensively due to their outstanding properties and their diverse technological applications in photovoltaic cells. Interestingly, single crystalline TiO2 nanorods (TiO2 NRs) offer more advantageous compared with TiO2 particles and polycrystalline. TiO2 NRs produce direct electrical pathways of photogenerated carriers as well as large surface areas between NRs. This work presents a synthesis of vertically-aligned and uniform TiO2 NRs that were hydrothermally grown on a transparent conductive fluorine-doped tin oxide (FTO) glass substrate. The substrates were seeded with TiO2 compact layer (CL) using titanium (IV) butoxide as a precursor in HCl solution. Various techniques, including field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were employed to investigate the morphology and crystalline structure of the prepared TiO2 NRs. FE-SEM results revealed that the TiO2 NRs showed a rod-like nanostructure which could increase the accessible surface area. In addition, the effect on Ti initial reactant concentration was optimized to have desirable properties on the TiO2 NRs’ density, diameter and length. As a result, the as-prepared TiO2 NRs could have very good prospects in high-performance perovskite solar cell as electron transporting layers.

Enhanced photoelectrochemical performance of TiO2 nanorod array films based on TiO2 compact layers synthesized by a two-step method.

An innovative two-step method perfectly prepared TCLs with different thicknesses, and then the TNA films based on TCLs were successfully prepared. The effects of different thicknesses of TCLs on the morphology and photoelectrochemical performance of TNA films were investigated. The results indicated that TCLs with appropriate thickness could effectively improve the morphology and photoelectrochemical performance of TNA films. Compared with the TNA films based on TCL5, TCL10 and TCL30, the TNA film based on TCL20 exhibited more ideal and comprehensive photoelectrochemical performance. Moreover, dye-sensitized solar cells (DSSCs) based on this TNA film achieved the highest Jsc (10.2054 mA cm−2), Voc (0.5737 V), PCE (3.3%) and Pout (3.31 mW cm−2).

Effect of compact TiO2 layer on structural, optical, and performance characteristics of mesoporous perovskite solar cells

We investigated the effect of a compact TiO2 (c-TiO2) layer on the structural, optical, and performance characteristics of mesoporous perovskite solar cells (mp-PSCs) with fluorine-doped tin oxide (FTO)/mesoporous TiO2 with or without c-TiO2 layer/perovskite/spiro-OMeTAD/Au structure. The mp-PSCs with the c-TiO2 layer exhibited a dense and pinhole-free perovskite film with a highly crystalline structure. On the other hand, the mp-PSCs without the c-TiO2 layer suffered from severe recombination problems at the perovskite/FTO interface, which was examined by impedance spectroscopy analysis. However, the c-TiO2 layer of the mp-PSCs played a significant role in reducing the recombination of carriers, due to the high carrier recombination resistance at the perovskite/FTO interface. As a result, the mp-PSCs with the c-TiO2 layer showed a high conversion efficiency of 15.51%, together with an open-circuit voltage of 1.04 V, a short-circuit current density of 20.44 mA/cm2 and a fill factor of 72.73%. In addition, the c-TiO2 layer minimized the hysteresis in the current density-voltage (J-V) curves measured for the mesoporous perovskite solar cells.

In-situ facile deposition of TiO2 hole blocking layers for efficient hole-conductor-free perovskite solar cells

A compact hole blocking layer is necessary for high efficient perovskite solar cell, which was usually fabricated by spin coating or spray pyrolysis with the followed annealing process, or vacuum deposition. Here, we deposited TiO2 compact layers by an in-situ room-temperature solvent method, which were applied as an effective hole blocking layer for hole-conductor-free perovskite solar cells with carbon electrodes. The thickness of the TiO2 compact layer can be easily regulated by the depositing time. By optimizing the TiO2 depositing time, the power conversion efficiency of hole-conductor-free perovskite solar cells was up to 10.66%.

Low temperature Zn-doped TiO2 as electron transport layer for 19% efficient planar perovskite solar cells

The properties of the perovskite solar cells (PSCs) are highly correlated with Fermi level, trap-state density and conductivity of inorganic electron transport layer. Metal elemental doping is an effective solution to largely improve the property of oxide semiconductor thin film. In this study, zinc dopant is successfully inserted into TiO2 crystal lattice using low-temperature solution-processed route. We find that Zn-doped TiO2 films possess less trap-state density and better conductivity, compared to undoped thin films, which contributes to the promotion of short circuit current. Ultraviolet photoelectron spectroscopy displays inserting Zn2+ into TiO2 compact layer can lift up TiO2′s Fermi level, which reasonably improved the carrier dissociation and transportation. Consequently, CH3NH3PbI3 PSCs based on 4.5% Zn-doped TiO2 has obtained 17.6% power conversion efficiency (PCE), which is nearly 27.5% higher than control device (13.8%). In addition, triple-cation mixed-halide PSCs based on 4.5% Zn-doped TiO2 has obtained a PCE of 19.04%, which is almost 13.7% higher than PCE of the device with undoped sample 16.75%. These findings offer a potential low-temperature doping method in TiO2 ETL for flexible high-performance PSCs.

Development of Next‐Generation Organic‐Based Solar Cells: Studies on Dye‐Sensitized and Perovskite Solar Cells

AbstractNext‐generation organic solar cells such as dye‐sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) are studied at the National Institute of Advanced Industrial Science and Technology (AIST), and their materials, electronic properties, and fabrication processes are investigated. To enhance the performance of DSSCs, the basic structure of an electron donor, π‐electron linker, and electron acceptor, i.e., D–π–A, is suggested. In addition, special organic dyes containing coumarin, carbazole, and triphenylamine electron donor groups are synthesized to find an effective dye structure that avoids charge recombination at electrode surfaces. Meanwhile, PSCs are manufactured using both a coating method and a laser deposition technique. The results of interfacial studies demonstrate that the level of the conduction band edge (CBE) of a compact TiO2 layer is shifted after TiCl4 treatment, which strongly affects the solar cell performance. Furthermore, a special laser deposition system is developed for the fabrication of the perovskite layers of PSCs, which facilitates the control over the deposition rate of methyl ammonium iodide used as their precursor.

TiO2/SnO2 Nanocomposites as Electron Transporting Layer for Efficiency Enhancement in Planar CH3NH3PbI3-Based Perovskite Solar Cells

Both TiO2 and SnO2 as electron transport layers (ETLs) are the most successful at producing high-efficiency perovskite solar cells (PSCs). Unfortunately, these layers usually require multiple treatments to improve device performance, especially for TiO2-based planar PSCs. Here, a simple, one-step, solution-based method is introduced for fabricating a TiO2/SnO2 nanocomposite ETL. Compared to a pristine TiO2 layer, partial incorporation of SnO2 nanoparticles in a thin compact TiO2 layer contributes to high electrical conductivity and suitable band-level alignment at the ETL/perovskite interface. Using the optimized TiO2/SnO2 nanocomposite ETL, methylammonium lead halide perovskite CH3NH3PbI3-based PSCs exhibit the champion efficiency of 16.8% (area, 0.13 cm2) with less current density–voltage (J–V) hysteresis, which is significantly superior to that of TiO2-based PSCs. Our work highlights that the successful use of TiO2/SnO2 nanocomposite ETL can offer an efficient method for further improvement of the performance for planar PSCs.