Interface Band Alignment Research Articles

Learning‐Effective Mixed‐Dimensional Halide Perovskite QD Synaptic Array for Self‐Rectifying and Luminous Artificial Neural Networks

AbstractA mixed‐dimensional heterostructure comprising nanomaterials with varying dimensions provides a promising structure for an artificial synapse for reconfigurable neuromorphic functions. In this study, an 8 × 8 memristor crossbar array based on a mixed‐dimensional heterostructure comprising Cs1−xFAxPbBr3 (0.00 ≤ x ≤ 0.15) quantum dots (QDs) and different dimensional interfacial nanomaterial layers between the Al and ITO electrodes is designed and fabricated. This array device exhibits a high yield and reliable self‐rectifying analog switching characteristics with low synaptic‐coupling (SC, up to 5.19 × 10−5) and light emission, facilitating stimuli response visualization and preventing undesired pathways in the network array. Furthermore, because the formamidinium (FA) concentration alters the QD size, thereby engineering interfacial band alignment in the heterostructure, the essential synaptic properties such as dynamic range, SC, and nonlinearity can be improved. Especially, as x increases from 0 to 0.11, the recognition accuracy for the MNIST patterns increases significantly, from 68.97% to 89.08%, even for single‐layer ANNs. The energy consumption required for a specific accuracy level is reduced by a factor of 25.15. The utilization of mixed‐dimensional perovskite QD‐based heterostructures in neural networks may provide desirable neuromorphic electronic functions with enhanced learning capability and energy efficiency, while preventing unwanted neural signals.

Density functional descriptions of interfacial electronic structure

Heterogeneous interfaces are central to many energy-related applications in the nanoscale. From the first-principles electronic structure perspective, one of the outstanding problems is accurately and efficiently calculating how the frontier quasiparticle levels of one component are aligned in energy with those of another at the interface, i.e., the so-called interfacial band alignment or level alignment. The alignment or the energy offset of these frontier levels is phenomenologically associated with the charge-transfer barrier across the interface and therefore dictates the interfacial dynamics. Although many-body perturbation theory provides a formally rigorous framework for computing the interfacial quasiparticle electronic structure, it is often associated with a high computational cost and is limited by its perturbative nature. It is, therefore, of great interest to develop practical alternatives, preferably based on density functional theory (DFT), which is known for its balance between efficiency and accuracy. However, conventional developments of density functionals largely focus on total energies and thermodynamic properties, and the design of functionals aiming for interfacial electronic structure is only emerging recently. This Review is dedicated to a self-contained narrative of the interfacial electronic structure problem and the efforts of the DFT community in tackling it. Since interfaces are closely related to surfaces, we first discuss the key physics behind the surface and interface electronic structure, namely, the image potential and the gap renormalization. This is followed by a review of early examinations of the surface exchange-correlation hole and the exchange-correlation potential, which are central quantities in DFT. Finally, we survey two modern endeavors in functional development that focus on the interfacial electronic structure, namely, the dielectric-dependent hybrids and local hybrids.

Probing Band-Alignment at the Interface of 3D/2D Perovskites for Solar Cell Applications

In this report, the effect of interfacial band-alignment in 3D/2D perovskite heterostructures on the performance of solar cells has been studied. The heterostructures have emerged as a preferred approach to slow down the degradation of 3D perovskites. We have incorporated three different organic spacers, namely butylammonium (BA+), phenethylammonium (PEA+), and ethanolamine (EA+), in forming the 2D perovskite layer over the top of a 3D triple-cation halide perovskite. The power conversion efficiency has been found to depend on the 2D perovskite. The band-energies of the 3D and the 2D perovskites, derived from scanning tunneling spectroscopy and Kelvin probe force microscopy, have showed that the EA+-based capping layer forms a type-II band-alignment at the 3D/2D interface and thereby facilitates charge separation. Our work depicts the necessity of probing the interfacial band-alignment while fabricating solar cells based on 3D/2D perovskites.

Understanding the Interfacial Reactions and Band Alignment for Efficient and Stable Perovskite Solar Cells Built on Metal Substrates with Reduced Upscaling Losses.

Conventional perovskite solar cells (PSC) built on transparent conductive oxide (TCO) glass face a fundamental challenge to retain fill factor (FF) for large-area upscaling due to series resistance loss. Building a perovskite solar cell on metal has the potential to reduce this FF loss and is promising for flexible applications. However, their efficiency and stability lag far behind their TCO counterparts. Herein, findings on the complex chemical reactions and degradation-promoting processes at different perovskite/metal (Cu, Au, Ag, and Mo) interfaces, which are closely linked with the inherent stability; and the interlayer engineering for perovskite/metal interface's band alignment, which plays an essential role in achieving high efficiency, are reported. Leveraging these findings, 21% power conversion efficiency (PCE) is achieved for 1 cm2 perovskite solar cells using a p-i-n top-illumination structure on a molybdenum substrate, the highest reported for a PSC built on metal. Notably, the FF and PCE losses due to area upscaling are remarkably reduced by one order of magnitude relative to the counterparts on conventional TCO glass, highlighting an alternative pathway for PSC upscaling and module design.

Nano-capillary induced assemble of quantum dots on perovskite grain boundaries for efficient and stable perovskite solar cells

In recent years, perovskite solar cells (PSCs) have propelled into the limelight owing to rapid development of efficiency; however, the abundant defects at the perovskite grain boundaries result in unwanted energy loss and structural degradation. Here, the grain boundaries of perovskite polycrystalline films have been found to act as nanocapillaries for capturing perovskite quantum dots (PQDs), which enable the conformal assemble of PQDs at the top interspace between perovskite grains. The existence of PQDs passivated the surface defects, optimized the interfacial band alignments, and ultimately improved the power conversion efficiency from 19.27% to 22.47% in inverted PSCs. Our findings open up the possibility of selective assembly and structural modulation of the perovskite nanostructures towards efficient and stable PSCs.

Space-Charging Interfacial Layer by Illumination for Efficient Sb2S3 Bulk-Heterojunction Solar Cells with High Open-Circuit Voltage

Solution-processed material systems for effective photovoltaic conversion are the key to low-cost and efficient solar cells. While antimony trisulfide (Sb2S3) is a promising photovoltaic absorber, solution-processed quality Sb2S3-based heterojunction systems for solar cells, particularly with an open-circuit voltage (Voc) higher than 0.70 V, are challenging issues. Here, a cadmium sulfide (CdS) interfacial engineering method is developed for the Sb2S3-based bulk-heterojunction (BHJ) solar cells with an efficiency of 6.14% and a Voc up to 0.76 V that is the highest one among solution-processed Sb2S3 solar cells. The prepared Sb2S3-based BHJ solar cells feature a Sb2S3 nanoparticle film interdigitated by a titania (TiO2) nanorod array with a nanostructured CdS shell as an interfacial layer on each TiO2 nanorod core. Upon understanding the interfacial interactions and band alignments in the TiO2-CdS-Sb2S3 system, the function of the CdS interfacial layer as a band-bended spatial spacer interacting strongly with both the TiO2 electron transporter and Sb2S3 absorber for increasing charge collecting efficiency is revealed; moreover, space-charging the band-bended CdS layer by illumination is found and a photogenerated interfacial dipole electric field model is proposed for understanding the high Voc subjected to the presence of the CdS interfacial layer. This work provides a conceptual guide for designing efficient inorganic heterojunction solar cells.

Non-volatile electric control of magnetic and topological properties of MnBi2Te4 thin films * * Notice: This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish

In this letter, we propose a mechanism to control the magnetic properties of topological quantum material (TQM) by using magnetoelectric coupling: this mechanism uses a heterostructure of TQM with two-dimensional (2D) ferroelectric material, which can dynamically control the magnetic order by changing the polarization of the ferroelectric material and induce possible topological phase transitions. This concept is demonstrated using the example of the bilayer MnBi2Te4 on ferroelectric In2Se3 or In2Te3, where the polarization direction of the 2D ferroelectrics determines the interfacial band alignment and consequently the direction of the charge transfer. This charge transfer, in turn, enhances the stability of the ferromagnetic state of MnBi2Te4 and leads to a possible topological phase transition between the quantum anomalous Hall (QAH) effect and the zero plateau QAH. Our work provides a route to dynamically alter the magnetic ordering of TQMs and could lead to the discovery of new multifunctional topological heterostructures.

Atomically Thin Twisted Heterostructure Optoelectronics Enhanced via vdW Interface Engineering

AbstractTwo‐dimensional (2D) heterostructures have sparked widespread interest in physics and device applications. The interfacial band alignment engineering of 2D heterostructures opens promising routes for high‐performance electronics and optoelectronics. In this study, a 2D Te/MoS2 interface is engineered by tailoring the lattice mismatch and distance, which changed the band alignment. The photocurrent is significantly increased by optimizing the interface alignment. The corresponding device is designed to function as an ultrasensitive photodetector with a light on/off ratio of 104, responsivity of ≈1047 A W−1, and detectivity of >5 × 1012 Jones, as well as a spectral detection capability of up to 1550 nm. The proposed methods are robust and versatile and can be used to produce desired electronics; hence, this study may broaden the scope of 2D heterostructure optoelectronics.

Universal Band Alignment Rule for Perovskite/Organic Heterojunction Interfaces

In contrast with the band alignment rule governing conventional semiconductor heterojunctions, the Fermi level position (i.e., work function, ϕpsk) of the perovskite and the differences in ionization energies of the organics are shown to dictate the band alignment and band offsets at perovskite/organic heterojunction interfaces. The experimental data show that the interface band alignments follow a universal alignment rule with three different energy windows: pinning of unoccupied molecular orbital states (LUMO) to the perovskite Fermi level, band offsets mediated by perovskite work functions, and pinning of occupied molecular orbital states (HOMO) to the perovskite Fermi level. The surface-passivated perovskites and several common native perovskites are all found to follow the same band alignment rule. Data scattering in measured band offsets, however, is observed on the same type of perovskites without proper surface passivation treatment. Solar cells made on the perovskites without surface passivation are also found to exhibit a large dispersive distribution in energy conversion efficiencies.

Depth-Dependent Post-Treatment for Reducing Voltage Loss in Printable Mesoscopic Perovskite Solar Cells.

The printable mesoscopic perovskite solar cells consisting of a double layer of metal oxides covered by a porous carbon film have attracted attention due to their industrialization advantages. However, the tens-of-micrometer thickness of the triple scaffold leads to a challenge for perovskite to crystallize and for the charge carriers to separate and travel to the electrode, which limits the open circuit voltage (VOC ) of such devices. In this work, a depth-dependent post-treatment strategy is demonstrated to synergistically passivate defects and tune interfacial energy band alignment. Two thiophene derivatives, namely 3-chlorothiophene (3-CT) and 3-thiophene ethylenediamine (3-TEA), are selected for the post-treatment. Energy-dispersive X-ray spectroscopy proves that 3-CT is uniformly distributed throughout the triple scaffold and effectively passivates the defects of the bulky perovskite, while 3-TEA reacts rapidly with the loose perovskite in the carbon layer to form 2D perovskite, forming a type II energy band alignment at the perovskite/carbon interface. As a result, the defect-assisted recombination is suppressed and the interfacial energy band is regulated, increasing the VOC to 1012mV. The PCE of the devices is enhanced from 16.26% to 18.49%. This depth-dependent post-treatment strategy takes advantage of the unique structure and provides a new insight for reducing the voltage loss.

Modulating Interfacial Carrier Dynamics via Spatial Conformation toward Efficient and Stable Perovskite Solar Cells

AbstractInterfacial defects result in serious carrier nonradiative recombination. The correlation between spatial conformation of modifiers and interfacial carrier dynamics is scarcely revealed. Here, an effective interfacial carrier dynamics and defect passivation modulation strategy via controlling spatial conformation of modification molecules is reported. Two kinds of similar Lewis base ligand molecules, biuret (BU) and dithiobiuret (DTBU), are employed to modify the surface of perovskite films. BU and DTBU can effectively passivate interfacial defects but the former is more effective than the latter on account of higher electronegativity and more advantageous molecular spatial arrangement. The planar symmetrical BU molecules can arrange compactly and orderly on the surface of perovskite films while the adsorbed DTBU molecules with a twisted asymmetrical structure are relatively chaotic. BU modification reduces interfacial energy offset, ameliorates improved interfacial energy band alignment, and speeds up hole extraction. In contrast, a much thicker adsorbed layer is yielded after DTBU treatment, which impedes carrier extraction and transfer and accordingly leads to grievous nonradiative recombination. The spatial conformation difference produces an inverse influence on device performance (positive for BU and negative for DTBU). The power conversion efficiency is much enhanced from 21.66% to 23.54% after BU modification along with improved stability.

Flexible Substrate‐Structured Sb2S3 Solar Cells with Back Interface Selenization

AbstractAntimony sulfide (Sb2S3) with a 1D molecular structure has strong bending characteristics, showing great application potential in flexible devices. Herein, the flexible substrate‐structured Sb2S3 solar cells is developed and improve device performances by the back interface selenization. The high‐quality Sb2S3 film with an optimal thickness of 1.8 µm, ensuring efficient spectra utilization, is deposited on flexible Mo foils by the rapid thermal evaporation technique. To solve the issues of back interfacial recombination and charge transport, the 20 nm MoSe2 layer between Sb2S3 film and Mo foil is fabricated by substrate selenization in the tube furnace. Further investigations indicate that the MoSe2 layer improves the interfacial energy band alignments and induces the [hk1] orientation of Sb2S3 film, thereby passivating defects and enhancing the carrier transport capacity. The flexible solar cell in the structure of Mo foil/MoSe2/Sb2S3/CdS/ITO/Ag, exhibiting good flexibility to stand thousands of bending, achieves an efficiency of 3.75%, which is the highest for Sb2S3 devices in substrate configuration. The presented flexible structure and back interfacial selenization study will provide new prospects for inorganic Sb2S3 thin film solar cells.

Interfacial band alignment and photoelectrochemical properties of all-sputtered BiVO4/FeNiOx and BiVO4/FeMnOx p–n heterojunctions

This work introduces FeMnOx as a novel effective cocatalyst for PEC water oxidation and provides simple tools for comprehending how interfacial effects influence the PEC performance of all-sputtered BiVO4/FeNiOx and BiVO4/FeMnOx p–n heterojunctions.

The interface microstructure and band alignment of hexagonal boron nitride/diamond heterojunctions

h-BNs with different orientations are directly grown on polycrystalline diamond due to minimization of the system energy. The diamond/h-BN heterojunction shows a type-II band alignment with a valence/conduction band offset of 2.08/1.86 eV.

Improving open-circuit voltage deficit by interface passivation via Li treatment in Cu2ZnSn(S,Se)4 solar cells

Li-doping via LiF post deposition treatment has achieved an enhanced open-circuit voltage in Cu2ZnSn(S,Se)4 solar cells. The Li treatment passivates the defects resulting in the modification of interface band alignment and enhanced charge excitation.

Stabilizing Buried Interface via Synergistic Effect of Fluorine and Sulfonyl Functional Groups Toward Efficient and Stable Perovskite Solar Cells

HighlightsAn effective buried interface stabilization strategy based on synergistic effect of fluorine and sulfonyl functional groups is proposed.The correlations between molecular structures, defect passivation, interfacial energy band alignment, perovskite crystallization and device performance are established.The device with KFSI achieves an impressive efficiency of 24.17%.

Synergistically optimizing thermoelectric performance of ZnO ceramics by interfacial band alignment and self-doping defects

ZnO is a promising thermoelectric ceramic material due to non-toxicity and abundance in resources. However, its thermoelectric performance is limited by the intrinsic low carrier concentration and high thermal conductivity. In this work, we synthesized the (1 − x)ZnO/xZnS (x = 0–0.05) powders by a two-step solution method followed by microwave sintering in an oxygen-deficient environment at 1000 ℃, and then produced the self-doped ZnO ceramics with ZnO/ZnS interfaces. The electrical and thermal properties was investigated from room temperature to 900 K. The ZnO/ZnS interface and self-doping significantly increased the electrical properties of ZnO ceramics, the electrical conductivity (σ) and Seebeck coefficient (α) increased simultaneously with temperature for (1 − x)ZnO/xZnS (x > 0), and the highest power factor (PF, 3675 µW·m−1·K−2) was obtained from 0.98ZnO/0.02ZnS at 900 K. At the same time, the ZnO/ZnS interfaces and self-doped defects greatly reduced the lattice thermal conductivity. Finally, the highest ZT value of 0.94 has been reached in 0.95ZnO/0.05ZnS at 900 K.

Tunable 0D/2D/2D Nanocomposite Based on Green Zn-Doped CuInS2 Quantum Dots and MoS2/rGO as Photoelectrodes for Solar Hydrogen Production.

Charge separation, transmission, and light absorption properties are critical to determining the performance of photoelectrochemical (PEC) devices. An important strategy to control such properties is based on using heterostructured materials. Herein, a tunable zero-dimensional (0D)/two-dimensional (2D) heterostructure is designed based on quantum dots (QDs) and 2D nanosheets (NSs). Specifically, eco-friendly Zn-doped CuInS2 QDs prepared by hot injection were anchored on hierarchical (2D/2D) MoS2/rGO (MG) NSs through a facile sonication-assisted method to develop a 0D/2D/2D heterojunction-based photoelectrode for solar hydrogen production. The interfacial structure and band alignment between the proposed 0D QDs and 2D/2D MG NSs were engineered by modulating the Zn molar ratio during the QD synthesis. As proof of concept, the optimized 0D/2D/2D photoanode exhibits almost five times higher PEC activity than MG/CuInS2 and MoS2/Zn-CuInS2 NSs due to the enhanced light absorption, efficient charge separation, and transmission. Zn doping and the presence of graphene are essential in enhancing performance in the proposed heterostructure, reducing recombination of charge carriers, and improving sunlight absorption. This work shows how optimal band alignment control and carbon addition can facilitate charge transfer, enabling the development of highly efficient PEC devices based on 0D/2D/2D heterostructure nanocomposites.

Modulation and Direct Mapping of the Interfacial Band Alignment of an Eco-Friendly Zinc-Tin-Oxide Buffer Layer in SnS Solar Cells

Modulation and Direct Mapping of the Interfacial Band Alignment of an Eco-Friendly Zinc-Tin-Oxide Buffer Layer in SnS Solar Cells

Stable and highly efficient all-inorganic CsPbBr3 perovskite solar cells by interface engineering with NiO NCs modification

The existence of considerable energy level differences and defects at interfaces between the CsPbBr3 film and the carbon electrode, have been critical bottlenecks to restrict the development of the photoelectric conversion efficiencies (PCEs) of all-inorganic CsPbBr3 perovskite solar cells (PSCs). Therefore, to solve this contradiction, the interface engineering has been applied into the interface of CsPbBr3/carbon through many passivators. However, most of the passivators reported previously are composed of organic ingredients, which is inconsistent with the concept of the “real all-inorganic” PSCs. Here, NiO nanocrystals (NiO NCs) with hole transporting behaviors were prepared by hydrothermal synthesis method and applied to modify the interface between the CsPbBr3 film and carbon electrode. After NiO NCs modified, the CsPbBr3 film with a smoother surface exhibits suppressed interface defects and appropriate interfacial energy band alignment, thereby decreasing the carrier recombination and improving the charge extraction ability. Eventually, by optimizing the concentrations of NiO NCs and the spin-coating cycles of CsBr methanol solution, the NiO NCs-treated device generates a champion efficiency of 9.19% with a short-circuit current (JSC) of 7.57 mA cm−2, an open-circuit voltage (VOC) of 1.57 V and a fill factor (FF) of 77.44%, in comparison with the pristine device with an inferior efficiency of 7.15%, a JSC of 6.92 mA cm−2, a VOC of 1.48 V and an FF of 69.64%. Furthermore, the NiO NCs modified devices show no significant degradation after 30 days in open-air conditions.