type-II Alignment Research Articles

UiO-66-NH2 Metal-Organic Frameworks with Embedded MoS2 Nanoflakes for Visible-Light-Mediated H2 and O2 Evolution.

Hydrogen evolution from water splitting by means of a photocatalytic approach is an ideal future energy source and free of fossil reserves, in contrary photocatalytic O2 evolution remains a bottleneck due to high over potential and low efficiency. For reasonable use of solar light, photocatalysts must be sufficiently stable and efficient toward harvesting of sunlight from both theoretical and practical viewpoints. In this regard, here we have prepared MoS2-modified UiO-66-NH2 MOF through a facile hydrothermal technique and evaluated its efficiency toward photocatalytic H2 and O2 evolution by water splitting in the presence of sacrificial agents. A couple of similar type of analyses have been studied previously; however, this analysis represents a diverse scientific approach on the basis of interfacial contact toward reveal the actual potential of nanoflakes MoS2 as well as UiO-66-NH2. In this regard the as-synthesized photocatalyst was well-characterized by XRD, FTIR, UV-vis diffuse reflectance spectra, FESEM, HRTEM, XPS, and BET analysis techniques, which provide sufficient evidence toward successful synthesis of the pristine materials and efficacious anchorage of MoS2 on the active surface of UiO-66-NH2 by the ionic interaction between Zr-O and S/Mo. Among the synthesized photocatalysts (3 wt %) MoS2/UiO-66-NH2 shows the optimum outcome toward H2 and O2 evolution, i.e., 512.9 μmol/h (4.37 times greater than bare UiO-66-NH2) and 263.6 μmol/h (4.25 and 11.32 times greater than bare UiO-66-NH2 and MoS2, respectively). The superior performance obtained by the composite is due to the synergistic effect of pristine UiO-66-NH2 and MoS2 which proceeds through a type-II interband alignment for the facile channelization of excitons. This investigation will bestow a beneficial blue-print to construct challenging photocatalysts and to find out the paramount performance toward photocatalytic water redox reaction.

Investigations of monoclinic- and orthorhombic-based (BxGa1−x)2O3 alloys

Gallium oxide has been attracting much interest due to its tremendous potential for power device application. The (BxGa1−x)2O3 ternary alloys of monoclinic and orthorhombic phases with the B-content covering the full composition were studied using first-principles density functional theory calculations. The effect of the B-content on the structural and electronic properties of (BxGa1−x)2O3 alloys is discussed. The formation enthalpy of the ternary alloys has been investigated, indicating the feasibility of synthesizing (BxGa1−x)2O3 alloys depending on the specified growth temperature condition. In addition, the increase in the B-content in (BxGa1−x)2O3 alloys generally leads to the decrease in lattice constants, implying possible tensile strain if grown on the Ga2O3 substrate. Our analysis on the electronic properties shows that all (BxGa1−x)2O3 alloys exhibit indirect gap property, in which the bandgap increases from 4.83 eV to 6.86 eV in the monoclinic phase and from 5.32 eV to 11.27 eV in the orthorhombic phase when the B-content increases from 0% to 100%. The band alignment between Ga2O3 and B2O3 in the (100)-direction is also presented, showing a type-II and type-I alignment for monoclinic-based and orthorhombic-based alloys, respectively. Our results showed an extremely large conduction band offset of 5.76 eV between orthorhombic-based Ga2O3 and B2O3 alloys. Our studies regarding the electronic and structural properties provide important insight regarding the potential of (BxGa1−x)2O3 alloys for III-oxide-based electronic and optoelectronic device applications.

Near-Direct Bandgap WSe2/ReS2 Type-II pn Heterojunction for Enhanced Ultrafast Photodetection and High-Performance Photovoltaics.

Pn heterojunctions comprising layered van der Waals (vdW) semiconductors have been used to demonstrate current-rectifiers, photodetectors, and photovoltaic devices. However, a direct or near-direct heterointerface bandgap for enhanced photogeneration in high light-absorbing few-layer vdW materials remains unexplored. In this work, for the first time, density functional theory calculations show that the heterointerface of few-layer group-6 transition metal dichalcogenide (TMD) WSe2 with group-7 ReS2 results in a sizable (0.7 eV) near-direct type-II bandgap. The interlayer IR bandgap is confirmed through IR photodetection, and microphotoluminescence measurements demonstrate type-II alignment. Few-layer flakes exhibit ultrafast response time (5 μs), high responsivity (3 A/W), and large photocurrent-generation and responsivity-enhancement at the hetero-overlap region (10-100×). Large open-circuit voltage of 0.64 V and short-circuit current of 2.6 μA enable high output electrical power. Finally, long-term air-stability and facile single contact metal fabrication process make the multifunctional few-layer WSe2/ReS2 heterostructure diode technologically promising for next-generation optoelectronics.

A type-II interband alignment heterojunction architecture of cobalt titanate integrated UiO-66-NH2: A visible light mediated photocatalytic approach directed towards Norfloxacin degradation and green energy (Hydrogen) evolution

Environmental pollution and energy scarcity is a major issue of the current scenario which forbear the progress of developing world. To overcome these problems towards a sustainable future, the utilization of sunlight by means of photocatalysis can be regarded as a best and suitable pathway. To validate this purpose, design and development of efficient heterogeneous photocatalyst for harvesting solar energy should be the major research concern for scientific community. In this regard herein, we have prepared a series of stable and efficient CoTiO3/UiO-66-NH2 p-n junction mediated heterogeneous photocatalyst by hydrothermal method. The functionalised linker of UiO-66-NH2 provided an intimate interfacial contact with CoTiO3 by Co/TiON ionic interaction, as proved by HRTEM and XPS analysis. Moreover the inverted V-shaped Mott-Schottky plot confirmed the junction formation in the optimised CoTiO3/UiO-66-NH2 material. In addition, EIS and PL analysis also provides sufficient evidence about the hindrance of active species recombination in composite as a result of p-n hetero junction. LC-MS characterization technique traces the assorted intermediate species produced in the course of photodegradation of Norfloxacin and confirms its complete degradation to corresponding CO2, H2O and NH4+ by the optimised CoTiO3/UiO-66-NH2. The highest photo-catalytic activity obtained towards Norfloxacin degradation is 90.13% and H2 production is 530.87 µmol in 1 h. The enhanced photo-catalytic reaction follows Type-II p-n hetero junction charge transfer mechanism and thus, paves a new way to design MOF based heterojunction photocatalyst for diverse photo catalytic performance.

Theoretical design of SnTe/GeS lateral heterostructures: A first-principles study

Using first-principles calculations, we theoretically designed new (SnTe)m/(GeS)n LHSs with the armchair interface connected by covalent bonds. We verified (SnTe)m/(GeS)n LHSs can be synthesized experimentally due to their small heat of formation. In contrast to the indirect bandgaps of pristine SnTe and GeS monolayers, the (SnTe)2/(GeS)2 LHS is a direct gap semiconductor with type-II alignment. The (SnTe)m/(GeS)n LHSs can achieve a transition from type-II to type-I alignment and from direct to indirect bandgap by increasing component units of (SnTe)m/(GeS)n LHSs. Meanwhile, the bandgaps of (SnTe)m/(GeS)n LHSs decrease monotonously as the component units increases. The conduction band minimum (CBM) and the valence band maximum (VBM) of (SnTe)2/(GeS)2 LHS are mainly distributed on SnTe and GeS, respectively. However, the CBM and VBM of (SnTe)4/(GeS)4 and (SnTe)6/(GeS)6 LHSs are dominated by SnTe. Furthermore, we found that the bandgap of (SnTe)2/(GeS)2 LHS can be effectively tuned by applying external strain.

Electrochemical deposition of p-type β-Ni(OH)2 nanosheets onto CdS nanorod array photoanode for enhanced photoelectrochemical water splitting

In this study, a novel three-dimensional (3D) CdS@Ni(OH)2 nanorod array (NRA) photoanode with a type-II band alignment and a p-n junction has been designed and constructed via a simple electrochemical deposition of hierarchical β-Ni(OH)2 nanosheets onto the surfaces of the CdS NRAs. The 3D CdS@Ni(OH)2 NRA photoanode fabricated under the optimal deposition current exhibits remarkably improved photoelectrochemical water splitting performance, and obtains a photocurrent density of up to 1.1 mA/cm2, 5-fold that of the pure CdS NRA photoanode. Most importantly, the solar-to-hydrogen conversion efficiency of the 3D CdS@Ni(OH)2 NRA photoanode is 3.3-fold higher than that of the pure CdS NRA photoanode at 0.67 V vs. RHE. The electrochemical and photoluminescence emission measurements confirm that the enhanced PEC water splitting capability of the prepared 3D CdS@Ni(OH)2 NRA photoanode is attributed to the efficient charge separation, which is achieved by the synergistic action of the type-II energy alignment and the p-n junction.

Type-II WS2–ReSe2 heterostructure and its charge-transfer properties

Abstract

Engineering the Band Alignment in QD Heterojunction Films via Ligand Exchange.

Colloidal quantum dots (QDs) allow great flexibility in the design of optoelectronic devices, thanks to their size-dependent optical and electronic properties and the possibility to fabricate thin films with solution-based processing. In particular, in QD-based heterojunctions, the band gap of both components can be controlled by varying the size of the QDs. However, control over the band alignment between the two materials is required to tune the dynamics of carrier transfer across a heterostructure. We demonstrate that ligand exchange strategies can be used to control the band alignment of PbSe and CdSe QDs in a mixed QD solid, shifting it from a type-I to a type-II alignment. The change in alignment is observed in both spectroelectrochemical and transient absorption measurements, leading to a change in the energy of the conduction band edges in the two materials and in the direction of electron transfer upon photoexcitation. Our work demonstrates the possibility to tune the band offset of QD heterostructures via control of the chemical species passivating the QD surface, allowing full control over the energetics of the heterostructure without requiring changes in the QD composition.

Designing WO3/CdIn2S4 type-II heterojunction with both efficient light absorption and charge separation for enhanced photoelectrochemical water splitting

WO3 is a typical photoanode material for photoelectrochemical (PEC) water splitting. However, the PEC activity of WO3 photoanode is limited by its poor visible light absorption as well as severe carrier recombination at the electrode/electrolyte interface. Herein, we integrate small-band-gap CdIn2S4 nanoplates with hydrothermally grown WO3 nanowall arrays to form into a three-dimensional (3D) WO3/CdIn2S4 heterojunction through a chemical bath deposition process. The synthesis parameters of CdIn2S4, including reaction time and temperature, have been tuned to optimize the PEC performance. The WO3/CdIn2S4 composite photoanode prepared at 50 °C for 5 h exhibits the highest photocurrent of 1.06 mA cm−2 at 1.23 V versus reversible hydrogen electrode without the presence of holes scavenger, which is about 5.9 times higher than that of bare WO3 photoanode. The band alignment between WO3 and CdIn2S4 is confirmed by the ultraviolet–visible light absorption spectra and ultraviolet photoelectron spectra. The PEC performance enhancement is attributed to the enhanced light absorption benefiting from the small band gap of CdIn2S4 and efficient charge separation originating from the type-II alignment between WO3 and CdIn2S4.

SiAs2/GeP2 heterostructure for solar cell: A first-principles calculation

The two-dimensional (2D) materials offer tremendous opportunities for efficient, ultrathin solar cells beyond conventional three-dimensional materials. In this work, we study the interfacial electrical properties and charge transfer characteristics of the SiAs2/GeP2 heterostructure by first-principles calculations. The SiAs2/GeP2 heterostructure shows a 2.25 eV bandgap and pronounced solar light absorption. Furthermore, the heterostructure presents a type-II alignment, and possesses a desirable power conversion efficiency (PCE) of up to 12.1%. These results reveal that SiAs2/GeP2 is promising for solar energy conversion in photovoltaic applications, and also provide a possible alternative for experiment scheme.

Perylene-3,4,9,10-tetracarboxylic acid accelerated light-driven water oxidation on ultrathin indium oxide porous sheets

Engineering the organic/inorganic nanocomposites by taking advantage of the high electrical conductivity of the inorganic semiconductors and the structure flexibility of the organic semiconductors (OSCs) provides chances to understand the structural and electronic contributions that give rise to increased activities, which is the imperious demand for methodical design of next-generation of oxygen evolution photocatalysts. Herein, perylene-3,4,9,10-tetracarboxylic acid (PTCAD) bonded porous In2O3 nanosheets, PTCAD/In2O3 NSs, were fabricated to elucidate the performance of OSCs in light harvesting and charge separation toward photo-driven oxygen evolution reaction (OER). PTCAD coupled strongly to the conduction band (CB) of In2O3 NS and type-II energy alignment was constructed between these two organic-inorganic components. Consequently, upon excitation, electrons injected smoothly from PTCAD to In2O3 NS, leaving holes behind to perform water oxidation, which results in accelerated charge separation and transportation. Associated with the large specific area, high-speed electron transmission channels, abundant oxygen vacancies and active sites provided by the In2O3 NS, the PTCAD/In2O3 composites demonstrated highly reduced band gap (BG), boosted and stable photocurrent, as well as largely reduced overpotential, suggesting promises for broadband-light-triggered OER. In addition to the synergistic effects in promoting charge separation and inhibiting electron-hole recombination, the π-conjugated molecule, PTCAD, played a role of manipulating the lattice plane of the In2O3 nanostructure without disturbing its porous 2D structure, providing another potential approach for enhancement of catalytic activity by regulating the crystal faces. Importantly, water oxidation over PTCAD/In2O3 NSs is indeed a proton-coupled electron transfer (PCET) processes, a key process for charge separation and water oxidation, which is significantly promoted by PTCAD. Ultimately, the photo-catalytic oxygen evolution yield enhanced greatly at the presence of PTCAD, indicating that our findings may provide clues for development of organic/inorganic hybrid semiconducting photocatalysts for solar fuels generation.

Impact of Dopant Aggregation on the EL of Blue Fluorescent Host-Dopant Emitters

We examined the characteristics of blue fluorescent organic light-emitting diodes (OLEDs) based on mCP:BCzVBi and CBP:BCzVBi systems which have Type-I and Type-II energy level alignments, respectively. As the BCzVBi concentration was increased from 5 wt% to 100 wt%, the OLEDs exhibited a 2.1-V voltage reduction and a 14-nm spectral redshift at 50 mA/cm $^{2}$ , indicating dopant aggregation which facilitates direct charge injection into the dopant. The mCP:BCzVBi OLED displayed a weak concentration dependence and attained a maximum luminance at a high concentration of 50 wt%. For CBP:BCzVBi, the luminance showed a stronger concentration dependence and peaked at a low concentration of 15 wt%. This discrepancy demonstrated a big impact of the energy level alignment on the charge and exciton behaviors in host-dopant systems. With a Type-I alignment, balanced charge injection and trapping in the dopant lead to suppressed singlet exciton-charge annihilation and mitigated quenching effects of dopant aggregation.

Study of wet and dry etching processes for antimonide-based photonic ICs

We report on the dry etch process parameters and the associated etch rates for target and mask materials, as well as surface roughness in an inductively coupled plasma (ICP) for the (AlGaIn)(AsSb)-compounds. The essential chemistry is based on Cl2 with the addition of N2 for sidewall passivation. The optimized ICP etch process is capable of producing high aspect ratio structures with smooth sidewalls. In situ reflectance monitoring with a 670-nm-wavelength laser was used to enable stop-etching at a material interface with high accuracy. Given the additional need for highly selective wet chemical etchants in the fabrication of GaSb based electronic and optoelectronic devices, an extensive investigation was also performed to examine numerous etch solutions. These etchants were listed with etch rates, selectivities, and surface roughness in order to validate their suitability for intended applications. Despite the frequent use of GaSb or InAsSb materials for etch stop layers against each other, devices where their unique type-II broken bandgap alignment is undesired require new selective wet etchants between GaSb and AlGaAsSb with good selectivity. All of the wet chemical and dry etching processes described here were optimized using an n-type GaSb substrate.

Strain and electric field modulated electronic structure of two-dimensional SiP(SiAs)/GeS van der Waals heterostructures

Type-II alignment appears in the SiP(SiAs)/GeS heterostructures, which can be tuned by strain and an electric field.

Electronic and optical properties of bilayer SnS with different stacking orders: A first principles study

Two-dimensional materials with tunable optical and electronic properties offer many interesting opportunities for optoelectronic devices and solar cells. Here, we report different stacking orders as an effective approach to tune the electronic and optical properties of SnS bilayers. Using the first principles density functional theory, the bandgap of the SnS bilayers is demonstrated to vary from 1.20 to 1.36 eV due to different stacking orders, wherein the AB-stacked SnS bilayer has a direct bandgap, different from AA- and AC-stacked ones. Furthermore, these SnS bilayer structures exhibit a strong light absorption over a wide range (∼1 to 6 eV), showing genuine potential for optoelectronic applications. When a MoS2 monolayer is combined with a p-type AB-stacked SnS bilayer, or a WS2 monolayer plus any of the above three stacking structures, the trilayer structures can be effective solar cell materials with a type-II heterojunction alignment.

A new insight into the enhanced visible light-induced photocatalytic activity of NaNbO3/Bi2WO6 type-II heterostructure photocatalysts

In this study, a series novel NaNbO3/Bi2WO6 heterojunction composites with a type-II alignment were fabricated via a facile wet impregnation method. The as-prepared photocatalysts were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), diffuse reflectance UV-Vis spectroscopy (DRS), photocurrent (PC) and electrochemical impedance spectroscopy (EIS) analyses. The 30 wt% NaNbO3/Bi2WO6 composite exhibited the best performance in the case of degrading rhodamine B (RhB) aqueous solution under visible light irradiation (λ > 410 nm), which was ∼2.5 times and ∼40 times that of pure Bi2WO6 and NaNbO3, respectively. The improved photocatalytic performance was further demonstrated by 2-chlorophenol under the same reaction conditions. This may be attributed to the enhanced electron-hole separation efficiency in Bi2WO6 with the assistance of NaNbO3, as well as the dye-sensitization effect of RhB dye itself. Intermediates produced during the reaction and RhB degradation pathway were investigated as well. Radical quenching experiments revealed h+ played the predominant role; O2·- functioned as well to some degree. Based on experimental results, the potential functioning mechanism was proposed, which is different from previously reported type-II heterostructure systems when Bi2WO6 works as the electron reservoir and O2·- is one of the dominant active species. The as-prepared photocatalyst composite exhibited excellent stability after repetitively running five times. Effects of several operating parameters on the catalyst performance including initial RhB concentration, catalyst dosage, reaction temperature and initial pH were also discussed. This study provides solid evidence for NaNbO3 to be a promising candidate for photocatalysis and gives out a novel photocatalytic mechanism of Bi2WO6-based heterostructures.

CdS sensitized sol-gel derived thin films of self-patterned micro-blocks of closely-packed SnO2 nanoparticles as high-performance photoanodes in alkaline solution of methanol

Materials with patterned micro-/nano-structures fabricated via self-organization for the conversion and utilization of solar energy are attractive. Thin films of self-patterned irregular micro-blocks of closely packed SnO2 nanoparticles have been achieved here as photoanodes in photoelectrochemical cells for the first time, which are accomplished facilely by annealing SnO2 gel coatings on conducting glass substrates at 500 °C. During the annealing, the gel coating evolves into closely packed SnO2 nanoparticles. They self-assemble into irregular micro-blocks (mostly about 10 μm in size), generating dense network micro-cracks (∼2 μm wide in average) around the micro-blocks and nano-cracks embedded in the micro-blocks due to the thermal contraction stress that the SnO2 nanocrystallization and self-assembly induce. Optimally, the self-patterned SnO2 film is well sensitized with nanolayers of CdS nanoparticles by successive ionic layer adsorption and reactions for six cycles. Under optimized conditions, the prepared SnO2/CdS film demonstrates an apparent anodic photocurrent density as high as 10 mA cm−2 while holding the potential at 0 V (vs. SMSE) in a photoelectrochemical cell with 2 M NaOH +1 M methanol under visible light illumination of 100 mW cm−2, which is among the highest record for SnO2/CdS photoanodes. We ascribe its high performance not only to the patterned micro/nano-structure and the type-II energy level alignments of the SnO2/CdS photoanode, but also to the photo-electro synergistic catalyses in methanol oxidation reaction.

Tunable Semiconductors: Control over Carrier States and Excitations in Layered Hybrid Organic-Inorganic Perovskites.

For a class of 2D hybrid organic-inorganic perovskite semiconductors based on π-conjugated organic cations, we predict quantitatively how varying the organic and inorganic component allows control over the nature, energy, and localization of carrier states in a quantum-well-like fashion. Our first-principles predictions, based on large-scale hybrid density-functional theory with spin-orbit coupling, show that the interface between the organic and inorganic parts within a single hybrid can be modulated systematically, enabling us to select between different type-I and type-II energy level alignments. Energy levels, recombination properties, and transport behavior of electrons and holes thus become tunable by choosing specific organic functionalizations and juxtaposing them with suitable inorganic components.

Theoretical study of triphenylamine-based organic dyes with mono-, di-, and tri-anchoring groups for dye-sensitized solar cells

Abstract In this report, DFT and TDDFT calculations used to explain the noticeable difference in the power conversion efficiencies (PCEs) of three reported triphenylamine-based organic dyes with mono-, di-, and tri-cyanoacrylic acid units as anchoring groups, and thiophene unit as π-bridges used as potential dyes in dye-sensitized solar cell applications. These dyes were showed the superiority of the multi-anchoring systems over the mono-anchoring system. The light was shed on the effect of various functionals, e.g., B3LYP, CAM-B3LYP, ωB 97 XD , M06, PBE0 and BHandHLYP on absorption spectra. The CAM-B3LYP functional was depicted the best among numerous adopted functionals which reproduced the experimental absorption data. The geometries, electronic structures and UV-Vis absorption spectra of the isolated dyes and their adsorbed dye@TiO2 complexes were calculated. The associated physical parameters that control the effectiveness of the cell, such as the light harvesting efficiency ( L H E ), hole and electron reorganization energies ( λ h o l e , and λ e l e ), and the driving force for electron injection ( Δ G i n j ) and dye regeneration ( Δ G r e g ) were computed and analyzed in order to determine their contributions to the open-circuit photovoltage ( V o c ) or the short-circuit photocurrent density ( J s c ), and correlate the structure with property. Also, charge transfer descriptors, such as the charge transfer distance ( D C T ), the amount of charge transferred ( q C T ), and dipole moment ( μ C T ) were investigated. The results reveal that the increasing of anchoring groups made significant influence on the PCE of the cells. The effect of mono-, di-, and tri-substituted anchored cyanoacrylic acid group(s) on the triphenylamine-TiO2 complexes has been explored on the frontier molecular orbitals, binding energies and absorption wavelengths. Among all the studied derivatives, electron injection energy barrier for TPA3T3A has been found the smallest which revealed that electron injection in this compound might be superior to other counterparts. Low-lying lowest unoccupied molecular orbital of TPA3T3A would favor it to stabilize thermodynamically. Moreover, TPA3T3A@TiO2 cluster was observed the most stable adsorption complex especially anchoring of TPA3T3A sensitizer at TiO2 cluster from B-side. Comprehensible intramolecular charge transfer has been observed from occupied to unoccupied molecular orbitals. The red shift in the absorption spectra has been perceived by increasing the number of anchoring groups, i.e., cyanoacrylic acid. The type-II band gap alignment between triphenylamine-based organic sensitizers and TiO2 is revealing that photovoltaic efficiency in these studied derivatives would be enhanced. Our quantum chemical analysis explored that these TPA derivatives especially tri-anchored dye would be proficient to be used in photovoltaic devices which would enhance the solar cell efficiency.

Commensurate versus incommensurate heterostructures of group-III monochalcogenides

First-principles calculations based on density-functional theory were performed to investigate heterostructures of group-III monochalcogenides (GaS, GaSe, InS, and InSe) and the effects of incommensurability on their electronic structures. We considered two heterostructures: GaS/GaSe, which has a lattice mismatch of 4.7%, and GaSe/InS, with a smaller mismatch of 2.1%. We computed the cost of having commensurate structures, and we also examined the potential energy landscape of both heterostructures in order to simulate the realistic situation of incommensurate systems. We found that a commensurate heterostructure may be realized in GaSe/InS as the interaction energy of this system with the monolayers assuming the average lattice constant is smaller than the interaction energy of an incommensurate system in which each layer keeps its own lattice constant. For GaS/GaSe, on the other hand, we found that the incommensurate heterostructure is energetically more favorable than the commensurate one, even when taking into account the energetic cost due to the lack of proper registry between the layers. Since the commensurate condition requires that one (or both) layer(s) is (are) strained, we systematically investigated the effect of strain on the band gaps and band-edge positions of the monolayer systems. We found that, in all monolayers, the conduction-band minimum is more than two times more sensitive to applied strain than the valence-band maximum; this was observed to strongly affect the band alignment of GaS/GaSe, as it can change from type-I to type-II with a small variation in the lattice constant of GaS. The GaSe/InS heterostructure was found to have a type-II alignment, which is robust with respect to strain in the range of $\ensuremath{-}2%$ to $+2%$.