Cu2ZnSnS4 as a hole-transport layer in triple-cation perovskite solar cells: Current density versus layer thickness

Cu₂ZnSnS₄ (CZTS) is a good candidate for cost-effective perovskite solar cells (PSCs) due to its direct bandgap with a value of 1.4–1.5 eV. In this study, we investigate CZTS ink as an inorganic hole-transport-layer (HTL) in CsMAFAPbIBr mixed halide PSCs. We study the cell efficiency and hole extraction from the perovskite layer for different thicknesses of HTL. The optimized device exhibits better hole selectivity, and the best efficiency of the device (12.84%) is achieved for the CZTS layer with a thickness of 159 nm. The prepared samples were also tested by open-circuit voltage decay analysis and electrochemical impedance spectroscopies. Results show that the optimized device effectively prohibits the electrons-holes recombination with a charge transfer resistance of 9.38 Ω cm². This work suggests that the optimal thickness of CZTS as an HTL in triple-cation PSC is about 159 nm by giving short-circuit current density of 23.69 mA cm^?2.     

Oriented rutile TiO2 nanorod arrays for efficient quantum dot-sensitized solar cells with extremely high open-circuit voltage

TiO₂ nanoparticles are typically employed to construct the porous films for quantum dot-sensitized solar cells (QDSCs). However, undesirable interface charge recombination at grain boundaries would hinder the efficient electron transport to the conducting substrate, giving rise to the decline of open-circuit voltage (V_oc). In this work, vertically aligned architectures of oriented one-dimensional (1D) TiO₂ nanorod arrays hydrothermally grown on substrates pave a way in designing highly efficient QDSCs with efficient radial-directional charge transport. SEM, TEM, XRD, and Raman spectroscopy were employed to characterize the as-prepared TiO₂ nanorods, showing the rutile phase with single-crystalline structure. The homogeneous deposition of CdS/CdSe QDs on the surface of TiO₂ nanorods has been achieved by in-situ grown strategies (i.e., successive ionic layer absorption and reaction, and chemical bath deposition). An extremely high V_oc value up to 0.77 V has been achieved for CdS/CdSe QDSCs based on the well-ordered 1D nanorod arrays. To the best of our knowledge, it is the highest V_oc reported for TiO₂-based QDSCs. Dependencies of photovoltaic performance, optical absorption, and interfacial charge behavior on the length of nanorods were systematically investigated. A 1.7 μm nanorod-array photoelectrode-based QDSC delivers a remarkable power conversion efficiency up to 3.57% under simulated AM 1.5 100 mW cm⁻² illumination, attributed to the balance of competition between the increase of QD loading and suppression of interfacial recombination. This work highlights the combination of QDs with high absorption coefficient 1D architectures possessing efficient charge transport for constructing high efficiency solar cells.     

Greatly enhanced photocurrent in inorganic perovskite [KNbO3]0.9[BaNi0.5Nb0.5O3‐σ]0.1 ferroelectric thin‐film solar cell

Inorganic perovskite [KNbO₃]_0.9[BaNi_0.5Nb_0.5O_3‐σ]_0.1 (KBNNO) ferroelectric thin films with narrow band gap (1.83 eV) and high room‐temperature remnant polarization (Pr = 0.54 μC/cm²) was grown successfully on the Pt(111)/Ti/SiO₂/Si(100) substrates by pulsed laser deposition. Ferroelectric solar cells with a basic structure of ITO/KBNNO/Pt were further prepared based on these thin films, which exhibited obvious external‐poling dependent photovoltaic effects. When the devices were negatively poled, the short‐circuit current and open‐circuit voltage were both significantly higher than those of the devices poled positively. This is attributed to enhanced charge separation under the depolarization field induced by the negative poling, which is superimposed with the built‐in field induced by the Schottky barriers at the interfaces between KBNNO and the two electrodes. When a poling voltage of ‐1 V was applied, the device showed a short‐circuit current as high as 27.3 μA/cm², which was by two orders of magnitude larger than that of the KBNNO thick‐film (20 μm) devices reported previously. This work may inspire further exploration for lead‐free inorganic perovskite ferroelectric photovoltaic devices.     

Tetramethylammonium based lead free perovskite active layer for solar cell application

Here we report the synthesis of a novel lead free organic-inorganic halide perovskite layer, tetramethylammonium tin tri-iodide (TMASnI₃), by simple and cost-effective chemical synthesis technique. The microstructural and optical studies confirm the formation of hexagonal perovskite structure with optical band gap ∼2.44 eV. A solar cell structure is fabricated by depositing the perovskite layer on zinc oxide thin film to demonstrate stable photovoltaic response under solar spectrum, where a thin layer of graphene oxide flakes on top of the perovskite layer acts as the charge transport layer. The open-circuit voltage (V_oc) and short circuit current density (J_sc) for this cell as extracted from the current-voltage measurement under one sun illumination of AM1.5 solar radiation are 0.60 V and 8.65 mA/cm², respectively. Without using any conventional hole transport layer, the power conversion efficiency (η) has been obtained as 1.92% which indicates the suitability of this perovskite material as an active layer for perovskite solar cell.     

Electrochemical deposition of flower-like ZnO nanoparticles on a silver-modified carbon nanotube/polyimide membrane to improve its photoelectric activity and photocatalytic performance

ZnO nanoparticles have been synthesized on a silver-modified carbon nanotube/polyimide (Ag-CNT/PI) membrane by electrochemical deposition. For comparison, a CNT/PI membrane was also obtained. The effect of the improved substrate on the structural, optical, photoelectric and photocatalytic characteristics of ZnO was examined. The flower-like ZnO nanoparticles was formed by the aggregation of nanosheets. The characterization of X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectra verified that the silver nanoparticles were distributed onto the nanotube. The absorption spectrum provided a band gap of 3.29 eV, which was confirmed by the band gap measurement. The photoelectric property of ZnO was investigated by current–voltage and open circuit potential measurements. The results demonstrated that the photoelectric activity and photocatalytic performance of ZnO were improved by the deposition.     

The effect of reduction time on the surface functional groups and supercapacitive performance of graphene nanosheets

Graphene nanosheets were prepared by reducing graphite oxide with hydrazine hydrate. The effects of reduction time on the structure and morphology of graphene nanosheets have been investigated. Their electrochemical performance in aqueous and organic electrolytes was also analyzed. With an increase of reduction time, the C and N contents of graphene nanosheets increased, while the specific surface areas and the specific capacitances decreased. Changes in reduction time produced a significant effect on the numbers as well as the types of oxygen and nitrogen functionalities. The graphene nanosheets, prepared by using a reduction time of 30 min have the highest specific capacitance of 192 F g^?1 in a 6 mol L^?1 KOH electrolyte. All prepared graphene nanosheets have a good rate performance and cycle stability.     

Heteroepitaxial growth of Cu2O films on Nb-SrTiO3 substrates and their photovoltaic properties

In this paper, p-type Cu₂O thin films have been epitaxially grown on n-type semiconducting (001) oriented Nb-SrTiO₃ (NSTO) substrates with different Nb doping concentration by pulsed laser deposition technique. X-ray diffraction and high resolution transmission electron microscopy reveal a cube-on-cube epitaxial relationship between Cu₂O and NSTO. It is found that the deposition temperature, the thickness of Cu₂O films and the Nb doping concentration of NSTO substrates have critical impact on the photovoltaic (PV) properties of the Cu₂O/NSTO heterojunction devices. A maximum PV performance is observed in ITO/Cu₂O/NSTO device when the deposition temperature, film thickness and Nb doping concentration of NSTO are 550 °C, 76 nm, and 0.7 wt% NSTO, respectively. The optimized PV output corresponds to the open circuit voltage, short-circuit current density, fill factor and photovoltaic conversion efficiency about 0.45 V, 1.1 mA/cm², 46% and 0.23%,respectively. This work offers an insight into the strategy for developing and designing novel optoelectronics of NSTO-based oxide heterostructures.     

Flexible piezoelectric energy harvesters with graphene oxide nanosheets and PZT-incorporated P(VDF-TrFE) matrix for mechanical energy harvesting

Flexible piezoelectric energy harvesters (PEHs) have attracted extensive interest because of their ability to transform mechanical energy into electric power. Here, PEHs were fabricated using P(VDF-TrFE)-based piezoelectric composite films containing lead zirconate titanate (PZT) powder and –OH-functionalized graphene (HOG) nanosheets (HOG-P/P). Among all composites, a high open-circuit voltage (Voc) of approximately 50 V_p-p and a maximum power density of 1.4 μW/cm² were obtained from a HOG-P/P PEH with 0.10 wt% HOG nanosheets and 15 wt% PZT under bending–releasing mode. Moreover, the PEH exhibited a stable voltage output after 3000 bending–releasing cycles. In addition, the PEH harvested mechanical energy from human body movements and generated an output voltage and current of 60 V and 8 μA during the finger bending–releasing process, lighting up 30 commercial white LEDs. The enhanced piezoelectric performance can be attributed to the introduction of HOG nanosheets and PZT powder. This work provides an effective strategy for improving the output performance of P(VDF-TrFE)-based PEHs.     

A Silicon Nanocrystal Schottky Junction Solar Cell produced from Colloidal Silicon Nanocrystals

Solution-processed semiconductors are seen as a promising route to reducing the cost of the photovoltaic device manufacture. We are reporting a single-layer Schottky photovoltaic device that was fabricated by spin-coating intrinsic silicon nanocrystals (Si NCs) from colloidal suspension. The thin-film formation process was based on Si NCs without any ligand attachment, exchange, or removal reactions. The Schottky junction device showed a photovoltaic response with a power conversion efficiency of 0.02%, a fill factor of 0.26, short circuit-current density of 0.148 mA/cm², and open-circuit voltage of 0.51 V.     

Photoresponse of high quality epitaxial BiFeO3 films grown through hydrothermal method and rapid microwave assisted method

High quality BiFeO₃ film with enhanced remanent polarization and magnetization attracts much interest for its great application potential in information storage and photoelectric devices. Here we grew single-crystal epitaxial BiFeO₃ film on SrTiO₃ substrate through hydrothermal method at low temperature, the film has a quality higher than any reported BiFeO₃ films grown through hydrothermal method. Furthermore, BiFeO₃ film was grown through a 25 min rapid microwave-assisted hydrothermal process. The two BiFeO₃ films exhibited obvious light response to periodically switching on and off of a LED light, and the film grown through microwave-assisted hydrothermal method produced a 4.7V open-circuit voltage exceeding the band gap of BiFeO₃ originating from the ferroelectric photovoltaic effect. These results demonstrate that hydrothermal and microwave-assisted hydrothermal method are simple, inexpensive and rapid to grow high quality epitaxial BiFeO₃ film with potential application in photoelectric detection and photovoltaic.     

The role of pressure on thin amorphous carbon films deposited using microwave surface wave plasma CVD

We report the effects of gas composition pressure (GCP) on the optical, structural and electrical properties of thin amorphous carbon (a-C) films grown on p-type silicon and quartz substrates by microwave surface wave plasma chemical vapor deposition (MW SWP CVD). The films, deposited at various GCPs ranging from 50 to 110 Pa, were studied by UV/VIS/NIR spectroscopy, atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and current–voltage characteristics. The optical band gap of the a-C film was tailored to a relatively high range, 2.3–2.6 eV by manipulating GCPs from 50 to 110 Pa. Also, spin density strongly depended on the band gap of the a-C films. Raman spectra showed qualitative structured changes due to sp³/sp² carbon bonding network. The surfaces of the films are found to be very smooth and uniform (RMS roughness < 0.5 nm). The photovoltaic measurements under light illumination (AM 1.5, 100 mW/cm²) show that short-circuit current density, open-circuit voltage, fill factor and photo-conversion efficiency of the film deposited at 50 Pa were 6.4 μA/cm², 126 mV, 0.164 and 1.4 × 10^− 4% respectively.     

Stable Tin Chloride Perovskite Sensitized Silver Doped Titania Nanosticks Photoanode Solar Cells with Different Hole Transport Materials

Perovskite sensitized solar cells (PSSCs) have recently been catapulted to the cutting edge of thin-film photovoltaic research and development because of their promise for higher power conversion efficiencies and ease of fabrication. In this work, an attempt has been made to fabricate CH₃NH₃SnCl₃ perovskite sensitized silver doped titania nanosticks photoanode solar cells with an efficient hole transport material (HTM), spiro-MeOTAD, poly(3-hexylthiophene-2,5-diyl) (PTTA) and CuI and attained light to electricity power conversion efficiency (PCE) of 10.46, 7.89 and 6.05 % respectively, under AM 1.5G illumination of 100 mW/cm² intensity. As well, PSSCs made with redox couple electrolytes namely quasi-solid state electrolyte (QSSE) and ionic liquid (IL) electrolyte exhibited the PCE of 4.92 and 3.20 % respectively. A metal oxide (HfO₂) layer is coated on the perovskite sensitized photoanode, which could increase the stability of PSSCs. The current density (Jsc)–open circuit voltage (Voc) study shows that PSSCs made with HTMs exhibited better fill factor and PCE. The electron impedance spectroscopy revealed that the electron lifetime (τ_n), electron mobility (µ) and charge collection efficiency (η_cc)in the PSSCs are in the order spiro-MeOTAD > PTTA > CuI > QSSE > IL. This work expresses that the nature of the HTM is essential for charge recombination and elucidates that finding an optimal HTM for the perovskite solar cell includes controlling the perovskite/HTM interaction.     

Insight of BaCe0.5Fe0.5O3−δ twin perovskite oxide composite for solid oxide electrochemical cells

One-pot synthesized twin perovskite oxide composite of BaCe_0.5Fe_0.5O_3−δ (BCF), comprising cubic and orthorhombic perovskite phases, shows triple-conducting properties for promising solid oxide electrochemical cells. Phase composition evolution of BCF under various conditions was systematically investigated, revealing that the cubic perovskite phase could be fully/partially reduced into the orthorhombic phase under certain conditions. The reduction happened between the two phases at the interface, leading to the microstructure change. As a result, the corresponding apparent conducting properties also changed due to the difference between predominant conduction properties for each phase. Based on the revealed phase composition, microstructure, and electrochemical properties changes, a deep understanding of BCF's application in different conditions (oxidizing atmospheres, reducing/oxidizing gradients, cathodic conditions, and anodic conditions) was achieved. Triple-conducting property (H⁺/O²⁻/e⁻), fast open-circuit voltage response (∼16–∼470 mV) for gradients change, and improved single-cell performance (∼31% lower polarization resistance at 600°C) were comprehensively demonstrated. Besides, the performance was analyzed under anodic conditions, which showed that the microstructure and phase change significantly affected the anodic behavior.     

Electric properties of a–C:H/a–C:N:H/aluminum structure

To obtain photovoltaic properties using carbon films without dependence on a Si substrate by drift of carriers, a photovoltaic cell consisted of aluminum (Al) and amorphous carbon films was fabricated. Two types of amorphous carbon were deposited on smooth Al substrates and on n-type Si by radio-frequency chemical vapor deposition. The first layer is nitrogen-doped hydrogenated amorphous carbon (a–C:N:H) film, and the second layer is hydrogenated amorphous carbon (a–C:H) film. Nitrogen atoms in a–C:N:H film were introduced as N–H structure. Both type of films were confirmed to be semiconductors on the basis of the temperature dependence of electroconductivity. The a–C:N:H/n–Si structure exhibited photovoltaic characteristics Furthermore, the a–C:H/a–C:N:H/Al structure cell also exhibited photovoltaic characteristics with an open-circuit voltage and short-circuit current of 5.5 mV and 0.83 μA/cm^− 2, respectively.     

Effect of yttrium-stabilized bismuth bilayer electrolyte thickness on the electrochemical performance of anode-supported solid oxide fuel cells

Lowering operating temperature and optimizing electrolyte thickness, while maintaining the same high efficiencies are the main considerations in fabricating solid oxide fuel cells (SOFCs). In this study, the effect of yttrium-stabilized bismuth bilayer electrolyte thickness on the electrical performance was investigated. The yttrium-stabilized bismuth bilayer electrolyte was coated on the nickel–samarium-doped composite anode/samarium-doped ceria electrolyte substrate with varying bilayer electrolyte thicknesses (1.5, 3.5, 5.5, and 7.5 μm) via dip-coating technique. Electrochemical performance analysis revealed that the bilayer electrolyte with 5.5 μm thickness exhibited high open circuit voltage, current and power densities of 1.068 V, 259.5 mA/cm² and 86 mW/cm², respectively at 600 °C. Moreover, electrochemical impedance spectroscopy analysis also exhibited low total polarization resistance (4.64 Ωcm²) at 600 °C for the single SOFC with 5.5 μm thick yttrium-stabilized bismuth bilayer electrolyte. These findings confirm that the yttrium-stabilized bismuth bilayer electrolyte contributes to oxygen reduction reaction and successfully blocks electronic conduction in Sm_0.2Ce_0.8O_1.9 electrolyte materials. This study has successfully produced an Y_0.25Bi_0.75O_1.5/Sm_0.2Ce_0.8O_1.9 bilayer system with an extremely low total polarization resistance for low-temperature SOFCs.     

Studies on chemical bath deposited SnS2 films for Cd-free thin film solar cells

Tin disulfide (SnS₂) is a simple binary metal chalcogenide and it has been proposed as a promising buffer material for Cd-free thin film solar cells. The present work explores the deposition of SnS₂ films by a facile chemical bath deposition at different deposition times in the range of 30–120 min. The effect of deposition time on the structural, optical and electrical properties was investigated. The as-grown SnS₂ films showed a hexagonal crystal structure with a high intensity (001) peak at 15.03°. The films showed shuttle shaped grains that were uniformly distributed across the surface of the substrate. The films showed an optical energy band gap in the range of 2.95–2.80 eV. PL spectra showed a strong emission peak in the wavelength range, 410–460 nm with the variation of deposition time. The SnS₂ films prepared at a deposition time of 90 min showed good crystallinity and morphology with low resistivity of 11.2 Ω-cm. A solar cell with device structure of Mo/SnS/SnS₂/i-ZnO/Al: ZnO/Ni/Ag was fabricated. The fabricated solar cell showed an efficiency of 0.91%, which validate the photovoltaic performance of SnS₂ films.     

Dicationic bis-imidazolium molten salts for efficient dye sensitized solar cells: Synthesis and photovoltaic properties

New dicationic bis-imidazolium salts based ionic liquids were synthesized to develop new electrolytes to improve photovoltaic properties of dye sensitized solar cells. Various properties of electrolytes such as viscosities, ion diffusion coefficients, charge transfer resistances and photovoltaic properties were studied. Electrochemical impedance spectroscopy has been performed to investigate diffusion coefficients and charge transfer resistances. Influence of polarity and chain length on the photovoltaic performance, was investigated. A DSSC employing the K34 (butyl-1,4-bis(3-methyl imidazolium iodide) gives an open-circuit voltage of 0.64 V, a short-circuit current of 17.11 mA/cm² and conversion efficiency of 5.60% under light intensity of 100 mW/cm² while the DSSC based on 1-butyl-3-methyl imidazolium iodide which is a reference ionic liquid exhibited 5.64% efficiency due to the lowest viscosity, highest diffusion coefficient.     

Construction of CaTiO3 nanosheets with boron nitride quantum dots as effective photogenerated hole extractor for boosting photocatalytic performance under simulated sunlight

Herein, titanate-based perovskite CaTiO₃ nanosheets were successfully designed via boron nitride quantum dots (BNQDs) to fabricate CaTiO₃/BNQDs catalyst. The as-fabricated composite catalysts were analysed by transmission electron microscope (TEM), scanning electron microscopy coupled with energy dispersive spectrometry (SEM-EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), X-ray diffraction (XRD), UV–vis spectroscopy (UV-DRS), photoluminescence (PL) and electrochemical impedance spectroscopy (EIS) techniques. SEM-Mapping analysis showed that the boron and nitrogen elements dispersed well over the CaTiO₃ surface which was useful for building electronic channels for rapid transport of photo-induced charge pairs. TEM images verified the attachment of BNQDs around the surface of host CaTiO₃ forming intimate interface while the distribution of chemical states was observed by XPS analysis demonstrating strong coupling effect between BNQDs and CaTiO₃ through Ti–O–N and Ti–O–B bonds. Moreover, PL and light absorption properties enhanced with the quantum confinement effect of BNQDs. As expected, the photocatalytic degradation rate of CaTiO₃/BNQDs was increased to k_app = 0.015 min^{? 1} with optimum BNQDs loading, which was 2.31 times folder than that of bare CaTiO₃ (0.006 min^{? 1}). The enhanced photocatalytic efficiency was observed for CaTiO₃/BNQDs than pristine perovskite on account of formation of electron tapping sites, decreased band gap energy and hindered recombination rate. On the other hand, in the presence of H₂O₂, the degradation percentage increased from 88.5% to 92.1% at the end of 120 min of irradiation while 96.8% of TC was quickly degraded within 60 min after activating with peroxymonosulfate which created strong sulphate radicals. Radical trapping tests indicated that the photo-generated holes were the primary active species in the photocatalytic mechanism. Moreover, CaTiO₃/BNQDs catalyst showed excellent stability in recycling tests. Besides, the possible degradation mechanism was proposed. This study shed light on the significance of BNQDs in the enhancement of the photocatalytic activities of titanate-based perovskite for effective degradation of tetracycline antibiotic in contaminated water.     

Quasi-free-standing monolayer and bilayer graphene growth on homoepitaxial on-axis 4H-SiC(0 0 0 1) layers

Quasi-free-standing monolayer and bilayer graphene is grown on homoepitaxial layers of 4H-SiC. The SiC epilayers themselves are grown on the Si-face of nominally on-axis semi-insulating substrates using a conventional SiC hot-wall chemical vapor deposition reactor. The epilayers were confirmed to consist entirely of the 4H polytype by low temperature photoluminescence. The doping of the SiC epilayers may be modified allowing for graphene to be grown on a conducing substrate. Graphene growth was performed via thermal decomposition of the surface of the SiC epilayers under Si background pressure in order to achieve control on thickness uniformity over large area. Monolayer and bilayer samples were prepared through the conversion of a carbon buffer layer and monolayer graphene respectively using hydrogen intercalation process. Micro-Raman and reflectance mappings confirmed predominantly quasi-free-standing monolayer and bilayer graphene on samples grown under optimized growth conditions. Measurements of the Hall properties of Van der Pauw structures fabricated on these layers show high charge carrier mobility (>2000 cm²/Vs) and low carrier density (<0.9 × 10¹³ cm⁻²) in quasi-free-standing bilayer samples relative to monolayer samples. Also, bilayers on homoepitaxial layers are found to be superior in quality compared to bilayers grown directly on SI substrates.     

Fabrication of highly transparent CsPbBr3 quantum-dot thin film via bath coating for light emission applications

Metal halide perovskite is not easy to form a film due to its high crystallinity, which makes it unfavourable for its application in self-luminous LED. Herein, we propose a film synthesis process for perovskite quantum dots (PeQDs) based on bath coating. The proposed method is low in cost, can be performed in an atmospheric environment at room temperature, and is suitable for the rapid mass production of closely stacked PeQDs on the deposition substrate with excellent luminous characteristics. By controlling the deposit time and rotation speed, the monolayer QD film can be achieved. The deposited monolayer QD film shows a high transmittance of up to 86% and a narrow FWHM of 18 nm. The device fabricated by monolayer QD film shows a low threshold voltage of 3 V, the maximum luminance of 150 cd/m², the maximum current efficiency of 0.085 cd/A, the maximum EQE of 0.027%, and the high color purity of 87%. Due to the above properties, monolayer QD film elements have potential in smart home appliances and wearable devices, especially AR glasses.