Photoelectric Conversion Properties Research Articles

A Microstructural Analysis of 2D Halide Perovskites: Stability and Functionality

Recent observations have demonstrated that the photoelectric conversion properties of perovskite materials are intimately related to the presence of superlattice structures and other unusual nanoscale features in them. The low-dimensional or mixed-dimensional halide perovskite families are found to be more efficient materials for device application than three-dimensional halide perovskites. The emergence of perovskite solar cells has revolutionized the solar cell industry because of their flexible architecture and rapidly increased efficiency. Tuning the dielectric constant and charge separation are the main objectives in designing a photovoltaic device that can be explored using the two-dimensional perovskite family. Thus, revisiting the fundamental properties of perovskite crystals could reveal further possibilities for recognizing these improvements toward device functionality. In this context, this review discusses the material properties of two-dimensional halide perovskites and related optoelectronic devices, aiming particularly for solar cell applications.

Liquid phase deposition/anodizing of TiO2 nanotube working electrode for dye-sensitized solar cells

With a high carrier transfer rate, anodizing TiO2 nanotubes (TNTs) are often used as the working electrode in dye-sensitized solar cells (DSSCs). However, the TNT length is restricted by the thickness of the Ti foil, which in turn limits the dye adsorption efficiency of the working electrode. To combat this problem, this study used liquid-phase deposition (LPD) to fabricate a TiO2 film on anodizing TNT. LPD allows for more rapid and even deposition of TiO2 films on the anodizing TNT structure than does vacuum deposition. Analysis revealed that LPD-TiO2 films fabricated at 3.33 nm/s increased the length of the TNT from 17.76 to 24.80 μm, and the dye adsorption capacity rose from 9.8 × 10−7 to 1.07 × 10−6 mol/m3. Testing confirmed that the photoelectric conversion efficiency of the DSSC device of the LPD/anodizing TNT increased from 2.43% to 2.85%, that the interface impedance of the DSSC device (R2) decreased from 132 to 41.5 Ω, and that the electron lifetime (τe) increased. In sum, the LPD-TiO2 film increased the thickness, dye adsorption efficiency and reduced the oxygen vacancies in the anodizing TNT; in other words, the coating effectively enhanced the photoelectric conversion properties of the DSSC device of the working electrode.

Self‐Assembly of a Semiconductive and Photoactive Heterobimetallic Metal–Organic Capsule

AbstractWe report the synthesis of a novel metal–organic capsule constructed from six pyrogallol[4]arene macrocycles, which are switched together by 16 FeIII and 16 CoII ions. This supramolecular structure is the first instance of a spheroidal heterometallic nanocage assembled through a one‐step metal–ligand coordination approach. This new assembly also demonstrates an important proof of concept through the formation of multiple heterometallic metal–metal interactions within the capsule framework. Photophysical and electrochemical studies of self‐assembled capsule films indicate their potential as semiconductors. These materials display unexpected photoelectric conversion properties, thus representing an emergent phenomenon in discrete metal–organic supramolecular assemblies.

Self-Assembly of a Semiconductive and Photoactive Heterobimetallic Metal-Organic Capsule.

We report the synthesis of a novel metal-organic capsule constructed from six pyrogallol[4]arene macrocycles, which are switched together by 16 FeIII and 16 CoII ions. This supramolecular structure is the first instance of a spheroidal heterometallic nanocage assembled through a one-step metal-ligand coordination approach. This new assembly also demonstrates an important proof of concept through the formation of multiple heterometallic metal-metal interactions within the capsule framework. Photophysical and electrochemical studies of self-assembled capsule films indicate their potential as semiconductors. These materials display unexpected photoelectric conversion properties, thus representing an emergent phenomenon in discrete metal-organic supramolecular assemblies.

Highly controllable synthesis of MAPbI3 perovskite nanocrystals with long carrier lifetimes and narrow band gap for application in photodetectors

Low-dimensional organic-inorganic hybrid perovskite materials have attracted much attention in photoelectric devices due to their exotic performance in optoelectronics compared with their bulk and thin-film counterparts. In this article, using a simple ligand-assisted deposition method, we successfully synthesized uniform methylammonium lead iodide (MAPbI3) perovskite nanorods, nanotriangles and nanocubes, and investigated their photoelectric properties after fabricated into photodetectors (PDs) on SiO2/Si substrates. It is found that the synthesized MAPbI3 nanorods not only have extremely small optical band gap (minimum of ~1.36 eV), but also have long photoluminescence (PL) lifetime (longest of ~7.81 μs) and high absolute PL quantum yields (maximum of ~ 45%), and the PL lifetime is more than about one order of magnitude higher than that the reported previously. The PDs based on MAPbI3 nanorods presented a wide spectral response “window” from 350 to at least 950 nm, and exhibited a photoresponsivity of 12.2 mA/W, a detectivity of 2.67 × 1011 Jones, the on/off ratio of more than 800, the rise/decay time constants of 18/25 ms, under the excitation at 405 nm. Further analysis suggests that the dramatically improved photo-electric conversion properties of the nanorods PDs could be closely related with their morphology dependent properties, including bandgap, PL lifetime, trap density (ntrap) and carrier concentration. These results provide a simple and effective method for preparing different morphology low-dimensional MAPbI3, and discuss the mechanism of morphology-dependent photoelectric performance of PDs, which is of great significance for potential applications in the field of photoelectronic devices.

Strain-engineered photoelectric conversion properties of lateral monolayer WS2/WSe2 heterojunctions

In order to explore the strain engineering for the electronic and optoelectronic properties of lateral monolayer heterojunctions, we develop a modified detailed balance method to search for the optimized power conversion efficiency (PCE) based on atomic-bond-relaxation mechanism. We find that the interface band alignment occurs a type II to type I transition at 7.8% tensile strain, and the optimized PCE of WS2/WSe2 lateral heterojunction can be up to ∼4.41%. Our method provides a vital guidance for the design of high-quality solar cell devices composed of a lateral two-dimensional heterostructure.

Study of the dimensions and photoelectric properties of TiO2 NTs prepared by the double Ti-Electrode oxidation method

In this paper, TiO2 nanotube (TiO2 NT) arraies are produced by a modified anodization method referred to as double titanium-electrode oxidation (DTEO). The effects of anodizing factors (e.g., anodizing voltage, time and the NH4F mass fraction of the electrolyte) on the dimensions of the TiO2 NTs are studied by a central composite design (CCD) experiment. From the results, it can be seen that within the scope of tests, the NT length (l) is strongly influenced by the interaction of the anodizing voltage and time. The tube pitch of the NTs (c) only depends on the anodizing voltage and has a positive correlation with it. Moreover, the photoelectric properties of the TiO2 NTs is analysed by using the photocurrent density (Jp) and dimensional parameters, such as the diameter-to-thickness ratio (di/w) of the NTs. In addition, there is a correlation between the di/w and the Jp values. The dimensions and photoelectric conversion properties of the TiO2 NTs can be controlled by the anodizing parameters used for the DTEO method.

Improved water oxidation via Fe doping of CuWO4 photoanodes: Influence of the Fe source and concentration* *Project supported by the National Natural Science Foundation of China (Grant No. 11204238) and the Natural Science Foundation of Shaanxi Province, China (Grant No. 2017JM1030).

Iron (Fe) was successfully doped in CuWO4 photoanode films with a combined liquid-phase spin-coating method via the dopant sources of Fe(NO3)3, FeSO4 and FeCl3. The microstructure of the prepared films was characterized by x-ray diffraction, scanning electron microscopy, and atomic force microscopy. The light absorption and photoelectric conversion properties were evaluated by the UV-visible absorption spectra and monochromatic incident photon-to-electron conversion efficiency. The chemical composition and element combination of the samples were examined by x-ray photoelectron spectroscopy. A linear sweep voltammetric and stability test (I–t) were performed with an electrochemical workstation. The results show that the samples are uniform with a thickness of approximately 800 nm and that the photoelectrochemical performance of the doped films is heavily dependent on the Fe source and dopant concentration. Upon optimizing the doping conditions of Fe(NO3)3 and the optimal source, the photocurrent density in the Fe-doped CuWO4 photoanode film is improved by 78% from 0.267 mA/cm2 to 0.476 mA/cm2 at 1.23 V vs reversible hydrogen electrode. The underlying causes are discussed.

A DFT study of influence of dichloromethane solvent and electric field on light absorption and electronic properties of two Quinoxaline-based solar cells

Geometric structure, molecular vibration, electronic and spectroscopic properties including frontier molecular orbitals, energy gap and global reactivity descriptors, Uv–vis absorption spectrum, charge separation degree, driving force of electron injection and generation and fluorescence lifetime of two D-A-π-A Quinoxaline-based indoline dyes, IQ4 and IQ22, were investigated theoretically in vacuum and dichloromethane (DCM) solvent by methods of density functional theory and time-dependent density functional theory, so as to gain more insight into the influence of DCM solvent and substitution of cyclopentadithiophene (CPDT) conjugated bridge for thiophene on photoelectric properties of the targets. Comparing IQ22 with IQ4, the larger dipole moment, narrower HOMO-LUMO energy gap and bathochromic shift in absorption benefit IQ22 optoelectric performance while weaker driving force of regeneration, smaller charge transfer rate, lower charge separation degree and shorter fluorescence lifetime are unfavorable to its photoelectric conversion properties. There are no significant differences of Jsc and Voc between title dyes based on the previous experiment, mainly due to the positive role and negative impact induced by substitution of CDPT into thiophene. Solvent effect caused by DCM makes the parameters more favorable to be applied in solar cells device.

CTAB-assisted solvothermal construction of hierarchical Bi2MoO6/Bi5O7Br with improved photocatalytic performances

We report the preparation and photoelectrochemical performance of three dimensional (3D) flower-like Bi2MoO6/Bi5O7Br nanosphere deposited on TiO2 NTA surface by a solvothermal method. The CTAB surfactant working as the morphology controlling reagent and bromine resource played significant roles in the Bi2MoO6/Bi5O7Br crystal growth and photocatalytic pollutant removal. The S-0.15 sample with hierarchical heterostructures showed the excellent photoelectric conversion and waste water purification properties. The visible light photocurrent and photovoltage of S-0.15 achieved 0.21 mA/cm2 and −0.37 V, and 73.43%, 47.77%, 93.81% and 69.40% of RhB, MO, MB and Cr(VI) underwent removal under solar irradiation. The O2–• radicals were the main active groups for RhB and MO decoloration, and all radicals including O2–•, •OH and hole could achieve the MB degradation. Moreover, the mechanism for the electron transportation was proposed by the calculation of energy band edge location in the triple photocatalyst. The novel triple photocatalyst with hierarchical structures would provide the platform for the efficient solar cells and photocatalysts.

Performance of photocatalytic cathodic protection of 20 steel by α-Fe2O3/TiO2 system

Photocathode protection is widely used in carbon steel for corrosion protection owing to its energy saving, environmental friendliness, convenience and high efficiency. In this work, α-Fe2O3 was used as a transition layer between 20 steel and TiO2 film, this structure is designed to improve the photocathode protection performance of TiO2 by hindering iron diffusion from matrix to TiO2 layer. Two different types of α-Fe2O3 were obtained by thermal and anodic oxidation on 20 steel. Then, TiO2 layers were prepared by spin-coating method on α-Fe2O3 transition layers. The effect of different α-Fe2O3 layer on the photocatalytic properties of TiO2 films was investigated. The photoelectric conversion properties of α-Fe2O3/TiO2 heterojunction films were evaluated by UV–vis absorption spectra, surface photovoltage spectroscopy (SPV), photoluminescence spectra (PL) and photocurrent density-time curves (I-t). Electro-chemical impedance spectroscopy (EIS) and potentiodynamic polarization curves were used to measure the corrosion resistance of 20 steel coupled with different α-Fe2O3/TiO2 film photoanodes. The samples pretreated by anodic oxidation demonstrate better photoelectric conversion efficiency than the samples obtained by thermal oxidation. Under sunlight irradiation, the α-Fe2O3/TiO2 film sample pretreated by anodic oxidation, as a photoanode, reduced the corrosion current density and corrosion potential of 20 steel in 0.5 M NaCl solution by 0.149 mA∙cm−2 and 297 mV, respectively, exhibiting superior photoelectro- chemical cathodic protection over the samples pretreated by thermal oxidation.

Synthesis and characterization of urchin-like CuO nanorod/TiCu-based metallic glass core-shell powders with surface photovoltage performance

The core-shell urchin-like powders (i.e. the microsized core composed of the residual metallic glass matrix powders and short CuO nanorod as the shell) were obtained through selective hydrothermal dealloying and annealed oxidation methods. TiCu-based metallic glass powders were used as precursors. Furthermore, the morphology and photoelectric conversion property of urchin-like CuO nanorod/metallic matrix powders were comprehensively investigated. These core-shell powders possess considerable surface photovoltage properties, and the sample annealed at 500 °C in air exhibits optimal surface photoelectric responses in visible light range (~600 nm). The surface photovoltage property was determined by the synergistic effect of crystallinity and surface morphology for the CuO phase. This study provides a strategy for in-situ synthesis of novel micro-nano-sized core-shell functional materials using facile dealloying and annealing of multiple-component alloys. The advantage of obtained products will further accelerate their applications in the green industry since this kind of micro-nano-sized powder material is easy to separate and recycle.

Solvothermal ion exchange preparation of Bi11VO19 to sensitize TiO2 NTs with high photoelectrochemical performances

Ag3VO4 nanograss was deposited on the surface of vertically grown TiO2 nanotube arrays (TiO2 NTs) by a successive ion layer adsorption and reaction (SILAR) method, and the Ag3VO4 nanograss was further transformed into Bi11VO19 by the solvothermal ion exchange method. The formation of Bi11VO19 was influenced by solvothermal intervals, and the TiO2 NTs/Bi11VO19 exhibited outstanding visible light response and photoelectrochemical activity. The TiO2 NTs/Bi11VO19 (3) prepared with solvothermal treatment for 3 h showed the optimal photoelectric conversion and photoelectrocatalytic (PEC) properties. The transient photocurrent density, photovoltage and charge carrier concentration achieved 9.53 mA/cm2, −0.29 V and 1.36 × 1020 cm−3, respectively. Furthermore, the PEC rate constants of TiO2 NTs/Bi11VO19 (3) for the MO, RhB and MB degradation achieved 3.56 × 10−3, 9.01 × 10−3 and 2.30 × 10−2 min−1, respectively. The PEC removal efficiency of Cr(VI) was 86.62%. The outstanding photoelectric activity drives the TiO2 NTs/Bi11VO19 photoelectrode prospective applications in waste-water purification and solar cells.

Theoretical investigation of the structural and electronic properties of Al-decorated TiO2/perovskite interfaces

Abstract Methylammonium lead iodide perovskites, CH3NH3PbI3, possess excellent photoelectric conversion properties and can be potentially applied as the next-generation light-harvesting layer of solar cells. However, the stability problems have been hindering their practical applications. The density-functional theory calculations have been performed to investigate the structural and electronic properties of Al-decorated TiO2/perovskite interfaces. Combined with the density derived electrostatic and chemical method, the bonding characteristics around the interfaces are explored. It is found that both interfacial Pb O and Ti I bonds are responsible for the stability of the interfaces, especially the interfacial Pb atoms making the formation of oxygen vacancies harder, which is beneficial for the performance of the solar cells. Furthermore, our calculations have shown that the properties of the TiO2/perovskite interfaces could be well improved by Al modification. The corresponding atomistic mechanisms that govern the stabilities of the TiO2/perovskite interfaces are also discussed.

Amorphous TiO2 granular nanodisks on porous Ti foam for highly effective solar cells and photocatalysts

Abstract Amorphous TiO2 granular nanodisks were synthesized by the simple anodization of porous Ti foam, and the morphology and photoelectrochemical performance were significantly influenced by anodization voltages. The investigation results showed that TiO2 nanotubes, nanodisks and nanospheres were fabricated at the anodization voltages between 15 V and 45 V, respectively, and TiO2 granular nanodisks showed the excellent photoelectric conversion and photoelectrocatalytic (PEC) properties. Under solar irradiation, the photocurrent density and photovoltage achieved 417.45 µA/cm2 and −0.23 V/cm2, and the PEC removal of MO, MB dyes and Cr (VI) achieved 61.05%, 93.77% and 51.82%. The excellent photoelectrochemical performance could be ascribed to the high surface area of Ti foam and multiple active adsorption sites of TiO2 granular nanodisks. The novel 3D photoelectrode would provide new insight in environmental remediation and solar energy conversion.

Assembling Bi2MoO6/Ru/g-C3N4 for Highly Effective Oxygen Generation from Water Splitting under Visible-Light Irradiation.

Water oxidation is a kinetically challenging reaction for photocatalytic overall water splitting. Producing one molecule of O2 will consume four electrons, so it is an extremely difficult obstacle for researchers. Here, a Bi2MoO6/Ru/g-C3N4 composite was obtained by a gentle hydrothermal method, which could oxidize water into O2 highly efficiently. The optimal O2 production reached 328.34 μmol·g-1·h-1 under visible light irradiation. Moreover, the catalyst presented excellent stability, as shown by a still sustentative 91.4% photocatalytic activity and invariant textural structure after seven recycling tests. The ternary material had the smallest resistance, which indicated that it has a good photoelectron conductive tunnel, and a rapid transfer route is proposed through Bi2MoO6 → Ru → g-C3N4 → NaIO3 (electron acceptor). The massive holes (h+) with high oxidative potential are surely enriched due to the quick electron migration, being fit for a large promotion of the multiple-electron water oxidative proceedings. Therefore, the metallic Ru provided a powerful bridge for efficient transfer of the interface electrons which could be beneficial to spatial separation of photoexcited carriers without the loss of the high redox capacity. Finally, it is proposed that the Ru-assisted electron transport and constituent synergy in Bi2MoO6/Ru/g-C3N4 composite play crucial roles to its enhanced light utilization, efficient photoelectric conversion property, and high-producing oxygen capability.

Novel diethylaniline D-A-π-A sensitizers for dye sensitized solar cells

Three diethylaniline D-A-π-A sensitizers were designed and synthesized with diethylaniline as the electron donor, benzothiadiazole as the auxiliary acceptor, aryl ring as π-bridge, and cyanoacrylic acid as the acceptor. Their photophysical, electrochemical and photoelectric conversion properties were measured and analyzed based on the difference of π-bridge. The sensitizer with thiophene π-bridge shows broader absorption region than the sensitizers with furan or benzene π-bridges, which brings about its improved incident photo-to-current conversion efficiency and accordingly higher JSC. In addition, DSSC based on the sensitizer with thiophene π-bridge shows the largest charge recombination resistance and superior VOC. Thus, among three diethylaniline sensitizers, dye with thiophene π-bridge achieves optimal photoelectric conversion efficiency 5.42% (VOC = 0.67 V, JSC = 11.51 mA cm−2, ff = 0.70) under simulated AM 1.5 G irradiation (100 mW cm−2).

Hydrothermal deposition of Cu2O-Ag nanoparticles co-sensitized TiO2 nanotube arrays and their enhanced photoelectrochemical performance

Cu2O-Ag nanoparticles were successfully deposited on the surface of TiO2 nanotube arrays (TiO2 NTs/Cu2O-Ag) by the one-pot hydrothermal method, and the visible light response, photoelectric conversion and photoelectrocatalytic properties of TiO2 NTs/Cu2O-Ag prepared with different Ag+ concentrations were investigated. The results indicated that the TiO2 NTs/Cu2O-Ag (0.05) photoelectrode showed the optimal photoelectrochemical performances, and the excellent photoelectrochemical activity was ascribed to the high solar absorption and effective electron transportation. Moreover, the active groups for the photodecomposition of dyes were explored, and the mechanism for the pollutant removal was tentatively proposed. The hydrothermal prepared Cu2O-Ag nanoparticles on TiO2 NTs would be attractive for the waste water purification and solar energy transformation.

Control synthesis of bismuth sulphide films and their application for laser detectors

Herein, we utilize a facile hydrothermal process for the synthesis of Bi2S3 films on the SnO2: F films (FTO) substrate. The structure, surface morphology and thickness of the samples were characterized by variously analysis method. The Bi2S3 films-based laser detectors exhibit excellent linear photocurrent characteristics, good sensitivity to 450 nm, 650 nm and 850 nm laser beam. Prolonging the reaction time was beneficial for the photoelectric performance of the Bi2S3 films-based laser detectors. The photoelectric conversion properties can be improved by optimizing the thickness of the films. The experimental results of this work can provide an additional opportunity for fabricating excellent photoconductive performance laser detectors.

Efficient planar perovskite solar cells based on low-cost spin-coated ultrathin Nb2O5 films

In planar perovskite solar cells (PSCs), the electron transport layer (ETL), with the function of transporting electrons and blocking holes, plays a significant role in determining the photoelectric conversion properties. Thus, it is crucial to exploit potential ETL materials for improved performance. Herein, we demonstrate efficient planar PSCs employing ultrathin Nb2O5 films as ETLs fabricated by a facile spin-coating method. The effects of the precursor concentration and annealing time of Nb2O5 on the photovoltaic performance are investigated in detail. The planar PSCs constructed with 0.02 M-prepared Nb2O5 films sintered for 1 h possess an optimized performance, giving rise to a champion efficiency of 14.82% with high reproducibility. The superior performance is ascribed to the appropriate conduction band position of Nb2O5, high transmittance, increased charge transport, and diminished charge recombination of the Nb2O5 film. The results demonstrate that the utilization of spin-coated Nb2O5 as the ETL provides a new platform to construct highly-efficient planar PSCs.