Band Edge Bending Research Articles

Multifunctional Phototransistor Based on Double Van der Waals Heterojunction with Reversed Band Edge Bending

AbstractDouble van der Waals heterojunctions (vdWHs) based on 2D materials showcase multifunctional properties, including anti‐ambipolar behavior and polarization‐sensitive photodetection capabilities, providing a new degree of freedom for the development of next‐generation integrated electronics and optoelectronics. Herein, this work reports an anti‐ambipolar transistor with high polarized photosensitivity based on MoS2/Ta2NiS5/WSe2 double vdWH with back‐to‐back type‐I band alignment. It demonstrates a noticeable negative differential transconductance with an ultrahigh peak‐to‐valley ratio of 4.3 × 104 and a bidirectional transconductance variation from 41.6 to −17.5 nS when VD = 2 V. It is ascribed to the effective gate‐modulation of the reversed band edge bending at the double vdWH interfaces. Additionally, the structure benefits from a photogating effect and the anisotropic Ta2NiS5 interlayer, achieving a peak responsivity of 120.58 A W−1 and a decent specific detectivity of 2.65 × 1012 Jones at VD = 2 V and Vg = 5 V and exhibiting an exceptional photocurrent anisotropic ratio of 15.31 via the photovoltaic effect under 635 nm light. These findings not only expand the potential applications of the advanced 2D Ta2NiS5 material but also offer valuable insights for the development of multifunctional optoelectronic devices leveraging 2D double vdWHs.

Surface p-type band bending and energy level alignment minimizes voltage loss in perovskite solar cells

Due to the significant energy level mismatch and contact energy loss between the perovskite absorber layer and p-type hole-transporting layer (HTL), there exists a large hole transport barrier between the perovskite absorber layer and HTL, which hinders hole transport and leads to lower open circuit voltage (VOC) in perovskite devices. Therefore, the surface contact process between the perovskite film and the hole-transporting layer becomes particularly important. Here, we doped cesium silver bismuth bromide (Cs2AgBiBr6) quantum dots (QDs) into ethyl acetate (EA) as an anti-solvent to achieve the formation of a bulk heterojunction structure with quantum dot solution on the surface of the MAPbI3 perovskite film. The perovskite film exhibits appropriate band edge bending and forms a p-type semiconductor. This facilitates the directed transport of photo-induced charge carriers to the hole-transporting layer, reducing carrier recombination losses and enhancing the collection efficiency of holes by the HTL. Through characterization experiments, we have found that this method significantly improves the VOC and photovoltaic conversion efficiency (PCE) of perovskite solar cells. The perovskite solar cells fabricated using this method show a better PCE with a VOC of 1.06 V.

Highly efficient ultrasound-driven Cu-MOF/ZnWO4 heterostructure: An efficient visible-light photocatalyst with robust stability for complete degradation of tetracycline

Metal-organic frameworks (MOFs) are a significant class of porous, crystalline materials composed of metal ions (clusters) and organic ligands. The potential use of copper MOF (Cu-BTC) for the sonophotocatalytic degradation of Tetracycline (TC) antibiotic was investigated in this study. To enhance its catalytic efficiency, S-scheme heterojunction was created by combining Cu-BTC with Zinc tungstate (ZnWO4), employing an ultrasound-assisted hydrothermal method. The results demonstrated that the Cu-BTC/ZnWO4 heterojunction exhibited complete removal of TC within 60 min under simultaneous irradiation of visible light and ultrasound. Interestingly, the sonophotocatalytic degradation of TC using the Cu-BTC/ZnWO4 heterojunction showed superior efficiency (with a synergy index of ∼0.70) compared to individual sonocatalytic and photocatalytic degradation processes using the same heterojunction. This enhancement in sonophotocatalytic activity can be attributed to the formation of an S-scheme heterojunction between Cu-BTC and ZnWO4. Within this heterojunction, electrons migrated from Cu-BTC to ZnWO4, facilitated by the interface between the two materials. Under visible light irradiation, the built-in electric field, band edge bending, and coulomb interaction synergistically inhibited the recombination of electron-hole pairs. Consequently, the accumulated electrons in Cu-BTC and holes in ZnWO4 actively participated in the redox reactions, generating free radicals that effectively attacked the TC molecules. This study offers valuable perspectives on the application of a newly developed S-scheme heterojunction photocatalyst, demonstrating its effectiveness in efficiently eliminating diverse recalcitrant pollutants via sonophotocatalytic degradation.

A novel perovskite solar cell comprising CsPbI2Br/Cs2SnI6 (CsGeI3) cascade absorbing bilayer and Cr2O3 electron transport material: A theoretical comparison study

In order to prevent the limitation on absorbing energies by a single-layer perovskite solar cells (PSCs), a cell comprising bilayer heterostructure in the form of FTO/Cr2O3/CsPbI2Br +Cs2SnI6 (CsGeI3)/spiro-OMeTAD/Au is simulated and its photovoltaic performance including incident photon-to-current conversion efficiency, fill factor, open circuit voltage and short circuit current is evaluated using SCAPS 1D software package. It is shown by introducing these structures, not only a wider range of the sunlight spectrum is exploited, but also by achieving a favorable band-edge bending as graded band gap, more charge carriers can be collected. Moreover, further improvement in the performance of devices is obtained by optimizing the thickness of absorbing layers and work function of the back electrode. The thermal stability of PSCs is investigated by varying the temperature in the range of 300–480 K and the effect of various electron transport materials (ETMs) on the performance of the cell is evaluated. Under optimized condition, it is found that the efficiencies of the cells with CsPbI2Br+Cs2SnI6 and CsPbI2Br+CsGeI3 bilayer heterostructures increase from 13.38% for non-heterojunction structure to 15.14% and 16.34%, respectively. Furthermore, the simulation results reveal that the photovoltaic cell made of CsPbI2Br+CsGeI3 absorbing layer having higher efficiency and greater thermal stability (compared to PSC made of CsPbI2Br+Cs2SnI6 absorbing layer) is an appropriate and promising candidate as efficient perovskite solar cell.

Construction of biochar-modified TiO2 anatase-rutile phase S-scheme heterojunction for enhanced performance of photocatalytic degradation and photocatalytic hydrogen evolution

Constructing step-scheme (S-scheme) heterojunction photocatalysts with high charge migration efficiency could enhance photocatalytic performance. In this study, biochar(BC)-modified TiO2 anatase(A)-rutile(R) phase S-scheme heterojunction photocatalysts was prepared through pyrolysis and hydrothermal methods. Results from various characterization techniques indicated a substantial improvement in the photocatalytic performance of BC/A/R-TiO2(550) under optimized conditions. This enhancement was attributed to the construction of a biochar-modified TiO2 anatase-rutile phase S-scheme heterojunction, which promoted the transfer of photogenerated carriers through the anatase-rutile interface. Moreover, when the interface of BC/A/R-TiO2(550) was irradiated with simulated sunlight, the built-in electric field, band edge bending, and coulomb force synergistically promoted the recombination of oxidized photogenerated electrons with reduced photogenerated holes while inhibiting the transfer of oxidized photogenerated holes with reduced photogenerated electrons. This phenomenon resulted in the high redox ability of both electrons and holes. Furthermore, photocatalytic degradation experiments revealed that the BC/A/R-TiO2(550) photocatalyst exhibited excellent photocatalytic activity, surpassing pure TiO2 and BC. The photocatalytic degradation performance of tetracycline (TC), ciprofloxacin (CIP), and norfloxacin (NOR) using BC/A/R-TiO2(550) was particularly high. Within 6 h, BC/A/R-TiO2(550) generated a hydrogen evolution amount of 159.7 μmol·h−1, which was 11.5 times higher than that of pure TiO2 (13.9 μmol·h−1). Additionally, the photocatalyst demonstrated good cycling stability. Through a series of studies on BC/A/R-TiO2(550), a possible photocatalytic mechanism on the as-formed S-scheme heterojunctions was proposed. Developing these novel S-scheme heterojunction photocatalysts presents a promising strategy for solar-driven photocatalysis, particularly in resolving the problems related to organic environmental pollutants.

Construction of Double S‐Scheme ZIF‐67@GDY/CuI Heterojunction by Graphdiyne (g‐CnH2n−2) Nanosheets‐Coated ZIF‐67 on Synergized Charge Transfer for Enhanced Photocatalytic Hydrogen Evolution

Graphdiyne (GDY) is a carbon allotrope material composed of sp and sp2 hybrid carbon atoms, which has been proven to be a good carrier for anchoring metal catalysts due to its abundant alkyne bonds. Herein, a double S‐scheme ZIF‐67@GDY/CuI heterojunction with graphdiyne (g‐CnH2n−2) nanosheets‐coated ZIF‐67 is prepared by a simple mixing method. The ZIF‐67 dodecahedron coated with GDY nanosheets constructed S‐scheme heterojunction by matching valence and conduction bands. The double S‐scheme heterojunction can maintain the strong redox ability of photogenerated electron–hole pairs well and promote more efficient charge transport. The excellent charge transport path is also attributed to the unique double S‐scheme heterojunction, which is confirmed by in situ X‐ray photoelectron spectroscopy. Moreover, the electron migration from ZIF‐67 to GDY generates an internal electric field (IEF), which improves the light energy utilization and charges separation efficiency under the condition of the IEF, band edge bending, and coulomb interaction. The optimal hydrogen production rate of ZIF‐67@GDY/CuI‐20 is 7.27 mmol g−1 h−1 under visible light irradiation, which is significantly increased by 4.75 times compared with the unmodified ZIF‐67. Herein, a new possibility for the construction of double S‐scheme heterojunction based on graphdiyne to improve photocatalytic performance is provided.

Novel MoSSe/Bi2WO6 S-scheme heterojunction photocatalysts for significantly improved photoelectrochemical and photocatalytic performance

Two-dimensional MoSSe nanoplates demonstrate low internal resistance and outstanding reduction potential, while Bi2WO6 nanoparticles exhibit zero-dimensional appearance and high oxidation potential. Herein, novel MoSSe/Bi2WO6 step-scheme (S-scheme) heterojunction photocatalysts (MSSB) were prepared to combine the properties of those two materials. These catalysts were confirmed to have lower internal resistance (as low as 0.07 kΩ), and higher carriers’ separation efficiency due to the well-contacted two-dimensional/zero-dimensional structure. More importantly, the heterojunction catalysts displayed both good oxidation and reduction performance which have been confirmed by the conducted catalytic tests. With an optimized Bi2WO6 loading ratio, degradation rates (k) and photocurrent density of the MSSB2 sample were 2.09, and 8.31 times more than that of MoSSe, as well as 1.77, and 26.27 times more than that of Bi2WO6. Active species (superoxide radical •O2− and hydroxyl radical •OH) were detected by the electron spin resonance tool which could infer that a S-scheme heterojunction has already constructed between the Bi2WO6 and MoSSe. Driven by the MoSSe and band edge bending, the e– on the conduction band of Bi2WO6 readily slid toward MoSSe and recombines with the h+ on the valence band of MoSSe, while retaining the powerful e– and h+ with high redox potential on the CB of MoSSe and VB of Bi2WO6. This work further provided a novel strategy for developing S-scheme nano-heterojunction catalysts and revealed their prospects in photoelectrochemistry and photocatalysis.

Modelling electronic transport in monocrystalline metal oxide gas sensors: from the surface kinetics to the experimental response

Gas sensing systems and devices based on metal oxides are widely spreading due to their high performance in terms of sensor response and relatively low costs. Despite several experimental studies and molecular simulations are available in the literature, a tool that can quickly predict the macroscopic sensor response, and potentially be used for predictive purposes, is still missing. In this work, we present a modelling approach based on finite-element simulations, using material electrical properties available in the literature. In a first approach, we derive the surface electron trap concentration from fitting the global sensor response. Then, we improve the model by considering the actual time-dependent experimental response. We consider sensors based on single SnO2 nanowires and show how our model predicts with a good agreement the experimental response vs. NO2, as a function of the working temperature and gas concentration, and additionally provides many other physical quantities of interest, such as the conduction band edge bending, the space charge and the width of the depletion layer. We further discuss ideas for improving the model and thus increasing its predictive potential with an engineering perspective.

Reduced graphene oxide assisted g-C3N4/rGO/NiAl-LDHs type II heterostructure with high performance photocatalytic CO2 reduction

Photocatalytic CO2 reduction has been considered as a potential way to solve the energy problem and the greenhouse effect. In this work, layered g-C3N4/rGO/NiAl-LDHs heterojunctions were prepared by using a hydrothermal method, the optimized composite exhibited enhanced photocatalytic CO2 reduction to CO (2.6 μmol h−1g−1) and CH4 (20 μmol h−1g−1) activity, which was 3.7 and 14.2 times higher than that of pure g-C3N4, respectively. According to the experimental and density functional theory calculation (DFT) results, it is believed that with the large contact interface and excellent electron mobility rGO could act as an electron transfer bridge to facilitate the rapid charge migration and separation between g-C3N4 and NiAl-LDHs. Thus, driven by the internal electric field, interfacial band edge bending, as well as the type II heterostructure, the activity of g-C3N4/rGO/NiAl-LDHs could be greatly enhanced. This work provides a possible way to rational design and fabrication of rGO-assisted composite systems with type II, Schottky, S-scheme, P-N and other heterojunctions.

A two-dimensional PtS2/BN heterostructure as an S-scheme photocatalyst with enhanced activity for overall water splitting.

Photocatalytic hydrogen production from water is a sustainable solution to the environmental pollution and energy crises. Encouraged by the successful synthesis of PtS2 and BN nanosheets and their suitable band edges, we have designed a PtS2/BN bilayer heterojunction and investigated its electronic and optical properties for the first time based on hybrid DFT calculations. In this system, the built-in electric field and band edge bending can retain useful electrons on the conduction band of BN and holes on the valence band of PtS2, which endow this system with a stronger redox ability. Meanwhile, this electric field can efficiently separate photoinduced electron-hole pairs and improve the photocatalytic efficiency. Compared with BN and PtS2 single layers, the PtS2/BN heterojunction with its smaller bandgap can make better use of visible and infrared light. Additionally, we have studied the effect of applied strain on the electronic and optical properties. This work aims to provide a method for constructing high-efficiency BN-based photocatalysts and illuminating the electron migration mechanism in step-scheme (S-scheme) heterostructures. We have found that the PtS2/BN bilayer heterojunction is a promising S-scheme photocatalyst for overall water decomposition.

2D/2D S-scheme heterojunction with a covalent organic framework and g-C3N4 nanosheets for highly efficient photocatalytic H2 evolution

The fabrication of S-scheme heterojunctions with fast charge transfer and good interface contacts, such as intermolecular π–π interactions, is a promising approach to improve photocatalytic performance. A unique two-dimensional/two-dimensional (2D/2D) S-scheme heterojunction containing TpPa-1-COF/g-C3N4 nanosheets (denoted as TPCNNS) was developed. The established maximum interfacial interaction between TpPa-1-COF NS and g-C3N4 NS may result in a π–π conjugated heterointerface. Furthermore, the difference in the work functions of TpPa-1-COF and g-C3N4 results in a large Fermi level gap, leading to upward/downward band edge bending. The spontaneous interfacial charge transfer from g-C3N4 to TpPa-1-COF at the π–π conjugated interface area results in the presence of a built-in electric field, according to the charge density difference analysis based on density functional theory calculations. Such an enhanced built-in electric field can efficiently drive directional charge migration via the S-scheme mechanism, which enhances charge separation and utilization. Thus, an approximately 2.8 and 5.6 times increase in the photocatalytic hydrogen evolution rate was recorded in TPCNNS-2 (1153 μmol g−1 h−1) compared to pristine TpPa-1-COF and g-C3N4 NS, respectively, under visible light irradiation. Overall, this work opens new avenues in the fabrication of 2D/2D π–π conjugated S-scheme heterojunction photocatalysts with highly efficient hydrogen evolution performance.

Construction of S-scheme 1D/2D rod-like g-C3N4/V2O5 heterostructure with enhanced sonophotocatalytic degradation for Tetracycline antibiotics

Pharmaceutically active compounds are an emerging water contaminant that resists conventional wastewater treatments. Herein, the sonophotocatalytic degradation of Tetracycline (TC) antibiotics as a model contaminant was carried out over a rod-like g-C3N4/V2O5 (RCN-VO) nanocomposite. RCN-VO nanocomposite was synthesized via ultrasound-assisted thermal polycondensation method. The results showed that the RCN-VO nanocomposite could completely remove the TC in water within 60 min under simultaneous irradiation of visible light and ultrasound. Moreover, the sonophotocatalytic TC degradation (a synergy index of ∼1.5) was superior to the sum of individual sonocatalytic and photocatalytic degradation using RCN-VO nanocomposite. Besides, the enhanced sonophotocatalytic activity of RCN-VO can be attributed to the 1D/2D nanostructure and the S-scheme heterojunction formation between RCN and VO where the electrons migrated from RCN to VO across the RCN-VO interface. Under irradiation, the built-in electric field, band edge bending and Coulomb interaction can synergistically facilitate the unavailing electron-hole pair recombination. Thereby, the cumulative electron in RCN and holes in VO can actively take part in the redox reaction which generates free radicals and attack the TC molecules. This study provides insight into a novel S-Scheme heterojunction photocatalyst for the removal of various refractory contaminants via sonophotocatalytic degradation.

Preparation of novel 0D/2D Ag2WO4/WO3 Step-scheme heterojunction with effective interfacial charges transfer for photocatalytic contaminants degradation and mechanism insight

The efficient photo-induced charges transfer/separation plays a critical role in enhancing photocatalytic performance of WO3. Herein, the novel visible-light-driven 0D/2D Ag2WO4/WO3 Step-scheme (S-scheme) heterojunction photocatalysts are synthesized by a facile hydrothermal method following with an in situ precipitation process. The special two-dimensional structure of WO3 not only acts as a suitable supporter for Ag2WO4 nanoparticles, but also shortens the transfer route of photo-induced charges. More importantly, the formed internal electric field as well as the band edge bending at the interface of Ag2WO4 and WO3 can further induce charges separation and retain the strong oxidation ability of holes on the VB of WO3. As a result, the obtained 0D/2D Ag2WO4/WO3 S-scheme heterojunction shows an excellent photocatalytic performance towards the degradation of oxytetracycline (OTC) and typical dyes, respectively. The specific degradation route based on the main intermediates of OTC and the possible mechanisms for this S-scheme heterojunction system are also investigated and discussed. This work provides the new insights into design of novel WO3-based S-scheme heterojunction photocatalysts for high-efficient antibiotic and dye degradation.

Two-dimensional GaTe/Bi2Se3 heterostructure: A promising direct Z-scheme water splitting photocatalyst

Among various photocatalytic materials, Z-scheme photocatalysts have drawn tremendous research interest due to high photocatalytic performance in solar water splitting. Here, we perform extensive hybrid density functional theory calculations to explore electronic structures, interfacial charge transfer, electrostatic potential profile, optical absorption properties, and photocatalytic properties of a proposed two-dimensional (2D) small-lattice-mismatched GaTe/Bi2Se3 heterostructure. Theoretical results clearly reveal that the examined het-erostructure with a small direct band gap can effectively harvest the broad spectrum of the incoming sunlight. Due to the relative strong interfacial built-in electric field in the heterostructure and the small band gap between the valence band maximum of GaTe monolayer and the conduction band minimum of Bi2Se3 nanosheet with slight band edge bending, these photogenerated carriers transfer via Z-scheme pathway, which results in the photogenerated electrons and holes effectively separating into the GaTe monolayer and the Bi2Se3 nanosheet for the hydrogen and oxygen evolution reactions, respectively. Our results imply that the artificial 2D GaTe/Bi2Se3 is a promising Z-scheme photocatalyst for overall solar water splitting.

Sulfur-doped g-C3N4/TiO2 S-scheme heterojunction photocatalyst for Congo Red photodegradation

Constructing step-scheme (S-scheme) heterojunctions has been confirmed as a promising strategy for enhancing the photocatalytic activity of composite materials. In this work, a series of sulfur-doped g-C3N4 (SCN)/TiO2 S-scheme photocatalysts were synthesized using electrospinning and calcination methods. The as-prepared SCN/TiO2 composites showed superior photocatalytic performance than pure TiO2 and SCN in the photocatalytic degradation of Congo Red (CR) aqueous solution. The significant enhancement in photocatalytic activity benefited not only from the 1D well-distributed nanostructure, but also from the S-scheme heterojunction. Furthermore, the XPS analyses and DFT calculations demonstrated that electrons were transferred from SCN to TiO2 across the interface of the SCN/TiO2 composites. The built-in electric field, band edge bending, and Coulomb interaction synergistically facilitated the recombination of relatively useless electrons and holes in hybrid when the interface was irradiated by simulated solar light. Therefore, the remaining electrons and holes with higher reducibility and oxidizability endowed the composite with supreme redox ability. These results were adequately verified by radical trapping experiments, ESR tests, and in situ XPS analyses, suggesting that the electron immigration in the photocatalyst followed the S-scheme heterojunction mechanism. This work can enrich our knowledge of the design and fabrication of novel S-scheme heterojunction photocatalysts and provide a promising strategy for solving environmental pollution in the future.

Band bending and valence band shifting of sub-monolayer TiO2 functionalized SnO2 nanowires

Sub-monolayer TiO2 over-layers were deposited on SnO2 nanowires (NWs) by atomic layer deposition. X-ray photoelectron spectroscopy, Mott–Schottky plots and photoluminance spectra were used to investigate the band structure and the separation of electron–hole pairs at the SnO2/TiO2 interface. The results showed that the valence band maximum of SnO2 NWs shifted to lower binding energies after functionalization, and significant upward band edge bending at the interface was confirmed. The rearrangement of energy band accelerated the separation of photo-generated electron–hole pairs leading to the improvement of photocatalytic degradation rate of methyl orange (MO, C14H14N3NaO3S) under UV irradiation.

Immobilization of facet-engineered Ag3PO4 on mesoporous Al2O3 for efficient industrial waste gas purification with indoor LED illumination

The immobilization of a photocatalyst on a proper support is pivotal for practical environmental applications. Herein, as a rising visible light photocatalyst, different facet-engineered Ag3PO4{111}, Ag3PO4{110}, Ag3PO4{100} and irregular Ag3PO4 were first immobilized on mesoporous Al2O3, then applied for photocatalytic removal of ppm-leveled NO under visible light illumination. Photocatalytic performances for NO removal by these immobilized Ag3PO4 were found to be highly facet-dependent, showing the degradation kinetics in the order of Ag3PO4{111} tetrahedra > Ag3PO4{110} rhombic dodecahedra > Ag3PO4{100} cubes > irregular Ag3PO4. The density functional theory (DFT) calculations were used to investigate the difference in the catalytic activity of Ag3PO4/Al2O3 with exposed {111}, {110}, and {100} facets. The experimental characterization and theoretical calculations all confirm that the {111} facets with high surface energy can not only facilitate adsorption/activation of O2 and H2O but also be beneficial to the generation of •O2− and •OH radicals, which result in significantly enhanced activity for NO oxidation. A modified band diagram showing diff ;erent degrees of band edge bending can explain these observations. A reaction pathway study based on both in situ FT-IR and molecular-level simulation of NO adsorption and transformation indicates that this Ag3PO4{111}/Al2O3 can efficiently adsorb NO and transform it into harmless nitrate products via NO → NO+ and NO2+ → nitrate or nitrite routes. The present work reveals the facet-dependent radical formation mechanisms of Ag3PO4/Al2O3, and also provides new perspectives for promoting environmental applications of immobilized photocatalysts.

Iodine-Optimized Interface for Inorganic CsPbI2Br Perovskite Solar Cell to Attain High Stabilized Efficiency Exceeding 14.

Recently, inorganic CsPbI2Br perovskite is attracting ever‐increasing attention for its outstanding optoelectronic properties and ambient phase stability. Here, an efficient CsPbI2Br perovskite solar cell (PSC) is developed by: 1) using a dimension‐grading heterojunction based on a quantum dots (QDs)/bulk film structure, and 2) post‐treatment of the CsPbI2Br QDs/film with organic iodine salt to form an ultrathin iodine‐ion–enriched perovskite layer on the top of the perovskite film. It is found that the above procedures generate proper band edge bending for improved carrier collection, resulting in effectively decreased recombination loss and improved hole extraction efficiency. Meanwhile, the organic capping layer from the iodine salt also surrounds the QDs and tunes the surface chemistry for further improved charge transport at the interface. As a result, the champion device achieves long‐term stabilized power conversion efficiency beyond 14%.

Structural, Optical, Electrical and Magnetic Studies of PANI/Ferrite Nanocomposites Synthesized by PLD Technique

In the present work PANI, 90%PANI/10%Ni0.8Zn0.2Fe2O4 and 90%PANI/10% Ni0.2Zn0.8Fe2O4 thin films were deposited successfully on the p-type Si-substrates by employing pulsed laser deposition technique (PLD), while the ferrite nanoparticles were synthesized by gel method. The interaction between ferrite nano powders and polyaniline has been studied by using X-ray diffraction (XRD), scanning electron microscope (SEM), UV–Vis spectrum, I–V characteristics and vibration sample micrometer (VSM). X-ray diffraction confirmed the presence of PANI and ferrite phases in the thin film nanocomposites. The average crystalline size value of 90%PANI/10%Ni0.8Zn0.2Fe2O4 and 90%PANI/10%Ni0.2Zn0.8Fe2O4 nanocomposite was estimated by utilizing Scherrer’s formula, they were found 20 nm and 25 nm, respectively. SEM images of the PANI and PANI/ferrite showed dense and inhomogeneous film morphology. The versatile optical properties of PANI/ferrite thin film nanocomposites are important for solar cell application. The obtained optical band gap for 90%PANI/10%Ni0.8Zn0.2Fe2O4 (2.45 eV) is less than pure PANI (2.8 eV) thin film. The lowering in the band gap value of 90%PANI/10%Ni0.8Zn0.2Fe2O4 nanocomposite film could be assigned to band edge bending phenomena. The light sensing behavior of the polyaniline/ferrite nanocomposites were examined at room temperature and showed higher response as compared to pure PANI film. Temperature dependence resistance characteristic was investigated in range between 25 and 100 °C under air atmosphere. The results showed that the dc resistance gradually decreases with the temperature increases and showing the semiconductor behavior of the prepared samples. The measured electrical resistance and band gap energy strongly suggest that the film with composition 90%PANI/10%Ni0.8Zn0.2Fe2O4 is a suitable candidate to be used in solar cell applications.

Graded Bandgap CsPbI2+xBr1−x Perovskite Solar Cells with a Stabilized Efficiency of 14.4%

Summary All-inorganic perovskite shows great potential for photovoltaic applications due to its excellent solar cell performance and atmospheric stability. Here, a CsPbI2+xBr1−x perovskite solar cell with a graded bandgap is explored using CsPbBrI2 and CsPbI3 quantum dots as component cells. Four strategies were pursued to boost the device performance. First, CsPbI2Br film was fabricated as the main absorber, with the component cell showing remarkable power conversion efficiency (PCE) as high as 13.45%. Second, by Mn2+ substitution, SCN− capping, and [(NH2)2CH]+ treatment, stable and high-mobility CsPbI3 quantum dot (QD) film was attained. Third, a halide-ion-profiled heterojunction was designed at the CsPbBrI2/CsPbI3 QD interface to achieve proper band-edge bending as graded bandgap for improved carrier collection. Finally, the CsPbI3 QD layer was optimized in the graded bandgap structure to achieve maximum overall light harvesting. As a result, the device achieved a PCE of 14.45%. This is the highest efficiency ever reported for inorganic perovskite solar cells.