Conduction Band Offsets Research Articles

Enhancing photovoltaic performance of dye-sensitized solar cells through TiO2/g-C3N4 nanocomposite photoanodes for improved charge carrier management

This study explores the enhancement of dye-sensitized solar cells (DSSCs) through the modification of porous TiO2 photoanodes by incorporating two-dimensional graphitic carbon nitride (g-C3N4) synthesized from urea. The combination of wide-bandgap TiO2 with narrow-bandgap g-C₃N₄ extends the optical response range of the TiO2 heterostructure composites from ultraviolet to visible light. The introduction of g-C3N4 with TiO2 to form a heterojunction significantly boosts the photovoltaic performance of the device by minimizing charge recombination at the photoanode-electrolyte interface. Upon optimizing the g-C3N4 loading, a peak power conversion efficiency (PCE) of 10.79 % is achieved, representing an impressive 42 % improvement over the pristine TiO2-based device. This enhancement is primarily attributed to the efficient separation of photogenerated charge carriers, facilitated by the type II band alignment between g-C3N4 and TiO2. This alignment, enabled by favorable conduction and valence band offsets, accelerates the separation of photogenerated carriers and prolongs electron lifetime.

Determination of the conduction and valence band offsets at the Co3O4/3C-SiC p-n heterojunction

The band offsets of semiconductor heterojunctions are critical parameters for the design of electronic and optoelectronic devices. In this work, we report the fabrication of a Co3O4/3C-SiC p-n heterojunction and the determination of the conduction band and valence band offsets at the Co3O4/3C-SiC heterojunction. Our results reveal that the Co3O4/3C-SiC p-n heterojunction exhibits a type-II band alignment, with a conduction band offset of 0.75 eV and a valence band offset of 0.96 eV. These experimental findings are crucial for the design and development of 3C-SiC devices for electronic and optoelectronic applications.

Epitaxial growth and band offsets of β -(ScxGa1− x)2O3 thin films grown on (100) β -Ga2O3 substrate

β-(ScxGa1−x)2O3 (x = 0–0.36) thin films were epitaxially grown on (100) β-Ga2O3 substrates by oxygen-radical-assisted pulsed-laser deposition. β-(ScxGa1−x)2O3 epilayers were coherently strained up to x = 0.30, although the presence of a structural disorder was implied when x > 0.2. The bandgap energies measured by reflection electron energy loss spectroscopy increased from 4.56 to 5.25 eV with increasing Sc content. In β-(ScxGa1−x)2O3 epilayers, a slightly negative bandgap bowing behavior with a bowing parameter of −0.4 eV was observed, resulting in a larger bandgap increase than in β-(AlxGa1−x)2O3 epilayers with identical x. X-ray photoemission spectroscopy measurement revealed that the valence-band and conduction-band offsets of β-(Sc0.17Ga0.83)2O3 epilayer with respect to β-Ga2O3 were 0.0 and 0.3 eV, respectively.

The first principle calculations of band offsets among Cs2(Ti, Zr, Hf)X6 double halide perovskites

This study investigates the band offsets among Cs2(Ti, Zr, Hf)X6 double halide perovskites. Valence band offsets (VBO) and conduction band offsets (CBO) were calculated using density functional theory (DFT) with the Perdew–Burke-Ernzerhof (PBE) functional and the hybrid Heyd–Scuseria–Ernzerhof (HSE) functional, employing the supercell technique. This technique offers greater accuracy and reliability by explicitly calculating the potential differences at the interface. A critical factor influencing the results is the contribution of the dipole potential (VD), which induces shifts in the VBO and CBO by approximately 0.2 to 0.6 eV relative to values predicted by the electron affinity rule. This discrepancy arises from the inclusion of interface-specific effects, such as charge redistribution and polarization. Additionally, the findings indicate that the energy band alignments among these compounds are type-I within the same group of halides, with nearly identical lattice constants for Zr- and Hf-based compounds due to their similar ionic radii. These results provide valuable insights for the design of heterostructures in electronic applications and highlight the potential of Cs2(Ti, Zr, Hf)X6 compounds as efficient materials for solar cells, light-emitting diodes, and photodetectors.

WSe2/n-GaN and WSe2/p-GaN heterojunction band alignment

Abstract In this work, we measured the band alignment of 2D/3D heterostructures of WSe2 on n-doped, pdoped, and intrinsic GaN by X-ray photoelectron spectroscopy (XPS). The WSe2/n-GaN heterojunction exhibits type-II band alignment, with measured valence band offset (VBO) and conduction band offset (CBO) values of 2.28±0.15 eV and 0.96±0.15 eV, respectively. On the other hand, the WSe2/p-GaN heterojunction shows type-I band alignment, with measured VBO and CBO values of 0.1±0.15 eV and 1.22±0.15 eV, respectively. The results show that doping has a significant effect on the arrangement of the energy bands of the heterostructure, and provides a reference for device applications based on heterojunctions.

Exploring the theoretical potential of tungsten oxide (WOx) as a universal electron transport layer (ETL) for various perovskite solar cells through interfacial energy band alignment modulation

Perovskite solar cells (PSCs) play a pivotal role in advancing renewable energy to achieve United Nation's Sustainable Development Goal 7 (SDG 7), which aims to ensure universal access to affordable, sustainable, reliable and modern energy services. Aiming to enhance the performance of PSCs by replacing the typically used electron transport layers (ETLs: TiO2, SnO2, ZnO etc.), we theoretically investigated the viability of tungsten oxide (WOX) as a promising ETL for PSCs. Moreover, the effect of altering the energy levels of WOX on cell performance has also been analyzed through simulation. Initially, 12 (twelve) PSC structures having the combination of different perovskite (PSK: CsPbBr3, CsPbI3, FAPbBr3, FAPbI3) absorber layers with different organic hole transport layers (HTLs: Spiro-OMeTAD, P3HT, PEDOT:PSS) and a fixed ETL of WOX were optimized numerically for comparing their performance. As CsPbBr3-based PSCs showed the best performance, further simulations were performed by varying some WOX/CsPbBr3 interface properties such as interface defect density, conduction band offset (CBO) between WOX and CsPbBr3, energy bandgap (Eg) of WOX etc. Finally, the best-performed PSCs were found for the Eg = 3.5 eV of WOX and the CBO of - 0.5 eV confirming the conduction band minimum (CBM) of WOX is lower than that of CsPbBr3 by 0.5 eV. A properly chosen WOX layer enhanced the efficiency of CsPbBr3-based PSCs up to 14.65 %, 14.52 % and 16.09 %, aproaching the Shockley-Queisser (S-Q) limit (16.37% for CsPbBr3-based solar cell) from the initial values of 11.39 %, 11.27 %, and 12.49 %, respectively. This study ensures WOX is a promising ETL for which a proper PSC structure having a suitable PSK and an HTL can improve cell performance. Moreover, the importance of modifying energy levels of ETL material in enhancing the performance of PSCs is explored. As a result, this study opens a path for the researchers to develop WOX having suitable CBM and Eg, so that it can be well-suited with a properly matched PSK material resulting in enhanced cell performance.

Metamorphic InGaAs/InAsPSb Quantum Well Light Emitting Diodes for Operation in the Short‐Wave Infrared Region

AbstractSolid‐state infrared sources designed to emit wavelengths above 2 µm often face challenges in achieving high emission efficiency, minimizing power consumption, and reducing fabrication costs. In response, a 2.4 µm wavelength light emitting diode (LED) is developed using metamorphic In0.83Ga0.17As/InAs0.3P0.65Sb0.05 multiple quantum well (MQW) heterostructures. The substantial conduction (94 meV) and valence band offsets (300 meV) within this type‐I MQW LED architecture result in strong carrier confinement, improving electron and hole wavefunction overlap. Despite a notable lattice mismatch of 2.0% between the MQWs and InP substrate, the resulting LED wafer exhibits exceptionally low surface roughness (1.1 nm) and well‐defined, sharp interfaces within the heterostructures. Furthermore, this MQW LED exhibits favorable emission properties, including a low turn‐on field, minimal efficiency droop, and stable emission wavelength across varying injection currents. These advancements underscore the potential of such short‐wave infrared emitters for scalable applications in fields such as inspection, optical on‐chip communication, and biomedical diagnostics.

Structural and interface band alignment properties of transparent p-type α-GaCrO3:Ni/α-Al2O3 heterojunction

Herein, we report epitaxial growth of p-type Ni doped gallium chromium oxide thin film on Al2O3 substrates and studied its band alignment properties with that of the substrate. Thin films are grown using the magnetron-sputtering technique. Synchrotron-based XRD measurements, performed in the coplanar and non-coplanar geometries, confirm high-quality single domain epitaxial growth of p-type α-GaCrO3:Ni. Pendellosung oscillations around the Bragg peak and transmission electron microscopy reveal the high interfacial quality of p-type α-GaCrO3:Ni films with the substrate. Thin film, thickness ∼200 nm, shows around 70% average transmission. The values of valence band and conduction band offsets are determined to be 2.79 ± 0.2 and 0.51 ± 0.2 eV, respectively, which confirm straddling gap band alignment at the heterojunction. This type of alignment creates a threshold barrier for the selective charge carriers and is useful in enhancing the performance of a wide range of devices, including UV photodetectors, metal oxide semiconductor high electron mobility transistors, and light emitters.

Analysis of Carrier Transport at Zn1-xSnxOy/Absorber Interface in Sb2(S,Se)3 Solar Cells.

This work explores the effect of a Zn1-xSnxOy (ZTO) layer as a potential replacement for CdS in Sb2(S,Se)3 devices. Through the use of Afors-het software v2.5, it was determined that the ZTO/Sb2(S,Se)3 interface exhibits a lower conduction band offset (CBO) value of 0.34 eV compared to the CdS/Sb2(S,Se)3 interface. Lower photo-generated carrier recombination can be obtained at the interface of the ZTO/Sb2(S,Se)3 heterojunction. In addition, the valence band offset (VBO) value at the ZTO/Sb2(S,Se)3 interface increases to 1.55 eV. The ZTO layer increases the efficiency of the device from 7.56% to 11.45%. To further investigate the beneficial effect of the ZTO layer on the efficiency of the device, this goal has been achieved by five methods: changing the S content of the absorber, changing the thickness of the absorber, changing the carrier concentration of ZTO, using various Sn/(Zn+Sn) ratios in ZTO, and altering the thickness of the ZTO layer. When the S content in Sb2(S,Se)3 is around 60% and the carrier concentration is about 1018 cm-3, the efficiency is optimal. The optimal thickness of the Sb2(S,Se)3 absorber layer is 260 nm. A ZTO/Sb2(S,Se)3 interface with a Sn/(Zn+Sn) ratio of 0.18 exhibits a better CBO value. It is also found that a ZTO thickness of 20 nm is needed for the best efficiency.

Determination of band offsets at the interfaces of NiO, SiO2, Al2O3, and ITO with AlN

The valence and conduction band offsets at the interfaces between NiO/AlN, SiO2/AlN, Al2O3/AlN, and ITO/AlN heterointerfaces were determined via x-ray photoelectron spectroscopy using the standard Kraut technique. These represent systems that potentially would be used for p-n junctions, gate dielectrics, and improved Ohmic contacts to AlN, respectively. The band alignments at NiO/AlN interfaces are nested, type-I heterojunctions with a conduction band offset of −0.38 eV and a valence band offset of −1.89 eV. The SiO2/AlN interfaces are also nested gap, type-I alignment with a conduction band offset of 1.50 eV and a valence band offset of 0.63 eV. The Al2O3/AlN interfaces are type-II (staggered) heterojunctions with a conduction band offset of −0.47 eV and a valence band offset of 0.6 eV. Finally, the ITO/AlN interfaces are type-II (staggered) heterojunctions with conduction band offsets of −2.73 eV and valence band offsets of 0.06 eV. The use of a thin layer of ITO between a metal and the AlN is a potential approach for reducing contact resistance on power electronic devices, while SiO2 is an attractive candidate for surface passivation or gate dielectric formation on AlN. Given the band alignment of the Al2O3, it would only be useful as a passivation layer. Similarly, the use of NiO as a p-type layer to AlN does not have a favorable band alignment for efficient injection of holes into the AlN.

The role of interface energetics in Sb2Se3 thin film solar cells

We comprehensively simulated the interface energetics at the Sb2Se3/CdS interfaces and showed its impact on device performance. The interface discontinuity, band bending at interface and energy level alignment generates interfaces issues and must be optimized for an optimal device performance. The design parameters for controlling interface. Metal contact work function preferably higher than electron affinity (EA) and Fermi level (EF) combined (EA + EF), should result in near Ohmic behaviour of contact. Secondly electron affinity of buffer could be tuned to achieve small positive conduction bandoffset (spike barrier) at absorber/buffer interface which lowers the chances of recombination through interface states. A pn + configuration with highly doped buffer layer, as compared to p-absorber, is favourable as it will extend depletion in absorber, providing additional drift to photo-generated carriers. Lastly, acceptor defect at Sb2Se3-CdS interface generate surface inversion and detrimental to performance. Donor defects occupying interface states are preferred condition for optimal device performance. We have compiled the optimal ranges for these controlling parameters, to achieve theoretically ideal values of energy level alignment and energetics, leading to optimal performance.

Performance optimization of ETL-free bifacial perovskite solar cells for flexible devices: A simulation study

The versatile applications of flexible perovskite solar cells (PSCs) have made them promising energy-harvesting devices in our daily lives. The electron transport layer (ETL)-free PSCs offer a flexible approach for harnessing energy while adding a bifacial approach that can further improve the device performance. In our study, we have optimized ETL-free bifacial PSCs via simulation by selecting the suitable front transparent electrode (FTE), hole transport layer (HTL), and rear transparent electrode (RTE). Our investigation reveals that a potential well-like structure, associated with a small conduction band offset (CBO) at the FTE/perovskite interface holds significant potential for enhancing the power conversion efficiency (PCE) of the device. The upward shift in the valance band of HTL promotes recombination and reduces the device performance. The bandgap and electron affinity of RTE highly influence the band alignment at HTL/RTE interface. The NiO/Ag/NiO (NAN) tri-layer RTE provides a better band alignment with HTL, and improves the charge transportation and, hence, the device performance. Moreover, the thickness of the interfacial defect layer at the FTE/perovskite and perovskite/HTL interfaces significantly impacts device performance. In optimizing the perovskite absorber layer, a perovskite bandgap of 1.4 eV shows maximum device performance. Our optimized device shows a remarkable PCE of >27% for both front and rear illumination.

Revealing the high-performance of a novel Ge-Sn-Based perovskite solar cell by employing SCAPS-1D

In this study, a novel Ge-Sn based perovskite solar cell (PSC) with the structure FTO/WS2/ FA0.75MA0.25Sn0.95Ge0.05I3/MoO3/Ag has been designed and thoroughly analyzed employing SCAPS-1D. Drawing attention from the work of Ito et al where a similar perovskite-based PSC displayed a poor performance of ∼ 4.48% PCE, in which a large conduction band offset (CBO) acts as a critical factor contributing to interfacial recombination and device deterioration. To address this issue, we presented WS2 as an electron transport layer (ETL) along with MoO3 as a hole transport layer (HTL), both possessing compatible CBO and valence band offset (VBO) with perovskite material. Through systematic simulations and optimizations, remarkable improvements in the PSC’s performance have been acquired, getting a power conversion efficiency (PCE) of 18.97%. The optimized structure involved a 50 nm MoO3 HTL, 350 nm FA0.75MA0.25Sn0.95Ge0.05I3 light-harvesting layer (LHL), and a 50 nm WS2 ETL. Bulk defect densities for the LHL and ETL were optimized to 1 × 1015 cm−3 and 1 × 1018 cm−3, respectively, significantly superior values than that of reported value in the literature. Particularly, the tolerable defect density of ETL has increased 1000 times more than the published literature. The interfacial tolerable trap density for MoO3/perovskite increased from 1 × 1014 cm−2 to 1 × 1016 cm−2. The study also explored the impact of defects on quantum efficiency, revealing a severe negative influence beyond a perovskite bulk defect density of 1 × 1017 cm−3. Light intensity analysis demonstrated a correlation between incident light reduction and device performance decay. Capacitance–Voltage (C-V) and Mott–Schottky (M-S) have been analyzed during the study. Finally, the total recombination of the optimized device concerning thickness has been analyzed along with the dark J-V characteristics. The comprehensive insights gained from this work are anticipated to accelerate the fabrication of mixed Ge-Sn based PSCs with improved efficiency, paving the way for commercialization in the photovoltaic industry.

The heterointerface characterization of BaF2 or MgF2 on the hydrogenated diamond by X-ray photoelectron spectroscopy

Group-II fluorides (BaF2 and MgF2) insulators are deposited on hydrogenated (C–H) diamonds by E-beam evaporator at room temperature. The bandgaps, chemical bonds and band offsets of fluorides are investigated by the high-resolution X-ray photoelectron spectroscopy (XPS) measurements. The XPS results show bandgap energies of 9.4 ± 0.2 eV for BaF2 and 9.7 ± 0.2 eV for MgF2 by F 1s energy loss spectra. The valence band offsets (ΔEV's) of BaF2/MgF2 on the C–H diamond are determined as 5.2 ± 0.2 and 4.8 ± 0.2 eV, respectively. There are both type II energy band configuration for BaF2 and MgF2 on the C–H diamond with conduction band offsets of 1.3 ± 0.2 eV and 0.6 ± 0.2 eV, respectively. The relatively oxygen-weak or oxygen-free fluoride/C–H diamond interface and large ΔEV suggest that fluorides are an excellent gate dielectric for the C–H diamond field-effect transistors with high hole mobility and low gate leakage.

Investigation of crystalline and band alignment properties of NiO/GaN and Ni0.5Co0.5O/GaN heterojunctions using synchrotron radiation based techniques

Epitaxial layers of NiO and Ni0.5Co0.5O have been deposited on GaN templates using RF magnetron sputtering deposition technique. The epitaxial relationship in out-of-plane and in-plane directions for NiO and Ni0.5Co0.5O layers with respect to GaN is [111]NiO(Ni0.5Co0.5O)∥[0001]GaN and [1̅10]NiO(Ni0.5Co0.5O)∥[1̅21̅0]GaN, respectively. The epi-layers are found to have two triangular domain structures oriented along [111] direction with an in-plane rotation of 60° with respect to each other. Photoelectron spectroscopy (PES) has been used to determine the valence band offset (∆EV) and the band alignment at the heterojunctions (HJs). The ∆EV at NiO/GaN and Ni0.5Co0.5O/GaN HJs are 1.2 ± 0.2 eV and 1.8 ± 0.2 eV, respectively. The conduction band offsets (∆EC) have also been estimated using the determined values of optical band gap (NiO: Eg = ∼ 3.5 eV; Ni0.5Co0.5O: Eg = ∼ 3.3 eV) from optical transmission measurements. The values of ∆EC are found to be 1.5 ± 0.2 eV and 1.9 ± 0.2 eV at NiO/GaN and Ni0.5Co0.5O/GaN HJs, respectively. A type-II band alignment is observed at both the HJs. Higher values of valence band and conduction band offsets are observed at Ni0.5Co0.5O/GaN HJ in comparison to NiO/GaN. These experimentally determined values of band offsets can be used to design wide band gap HJ based devices like photodetectors, where higher values of band off-set at the Ni0.5Co0.5O/GaN HJ can be utilized to confine the carriers.

Design and optimization of Cs2SnI6 based inorganic perovskite solar cell model: numerical simulation

To overcome the drawbacks of high lead toxicity and poor corrosion resistance of lead-based perovskite solar cells (PSCs), and to compensate for the poor air stability of Sn2+ compound-based perovskite, Cs2SnI6 (Sn4+ compound) is selected as the absorber for the PSC in this study. Using FTO/ETL/Cs2SnI6/HTL/Au as the model, the high-performance non-toxic inorganic PSC structure is explored through theoretical simulation and calculation by SCAPS-1D. The conduction band offsets (CBO) and valence band offsets (VBO) of commonly used electron transport layer materials (ETMs), hole transport layer materials (HTMs), and Cs2SnI6 are calculated based on electron affinity potential (χ) and bandgap (E g ). Then, by analyzing the pn junction composed of ETL and HTL and the bandgap structure at the n-i, i-p interfaces, the most matching n-i-p planar heterojunction model, FTO/IGZO/Cs2SnI6/Cu2BaSnS4/Au, was selected. Finally, by analyzing and adjusting the material thickness, defect density of each layer, operation temperature, the optimal performance of PSC was determined to be 30.39% power conversion efficiency (PCE), 1.27 V open circuit voltage (V oc ), 28.46 mA cm−2 short circuit current (J sc ), and 84.02% fill factor (FF). A new and more efficient PSC is proposed in this study, providing some terrific clues for finding high-quality alternatives to lead-based PSCs.

Analysis of lead free CsSnBr3 based perovskite solar cells utilizing numerical modeling

In this study, we propose several CsSnBr3-based PSC configurations using the Solar Cell Capacitance Simulator (SCAPS-1D), incorporating various efficient Electron transport layers (ETLs) such as TiO2, PCBM, WS2, SnO2, ZnO, IGZO, C60, and Hole transport layers (HTLs) like CBTS, CFTS, CuO, CuI, Spiro-OMeTAD, PEDOT:PSS, P3HT, CuSbS2, CuSCN, and Cu2O. Numerical simulation results reveal that the device structure ITO/WS2/CsSnBr3/Cu2O/Au exhibits outstanding power conversion efficiency (PCE), retaining the closest photovoltaic parameter values among 70 different configurations. In this configuration, WS2 served as the ETL, and Cu2O acted as the HTL. This device achieved an outstanding peak PCE of 20.02%. It also boasted a high open circuit voltage (Voc) of 1.23 V, a short circuit current density (Jsc) of 19.32 mA cm−2, and an impressive fill factor (FF) of 84.18%. In comparison, devices utilizing materials like TiO2, PCBM, SnO2, ZnO, IGZO, and C60 yielded PCE values of 19.72, 19.73, 19.72, 19.73, 19.72, and 15.60%, respectively. Furthermore, for the seven best-performing configurations, we investigated the effects of CsSnBr3 absorber thickness, absorber-acceptor doping density (NA), conduction band offset (CBO), ETL doping density (ND), Capacitance–Voltage (C-V), Mott–Schottky (M-S) characteristics, generation and recombination rates, series resistance (Rse), shunt resistance (Rsh), temperature, current–voltage characteristics (J-V), and quantum efficiency (QE) on performance metrics. Our findings indicate that all seven ETLs, when combined with Cu2O HTL, can serve as excellent materials for fabricating high-efficiency CsSnBr3-based PSCs with the ITO/ETL/CsSnBr3/Cu2O/Au structure. To validate our results, we compared the simulation outcomes obtained with SCAPS-1D for the best seven CsSnBr3-PSC configurations with previously published research works. This comprehensive simulation study opens a promising avenue for the cost-effective production of high-performance, lead-free CsSnBr3-based PSCs, contributing to a greener and pollution-free environment.

Estimation of the band alignment of metal/AlScN interfaces by hard X-ray photoelectron spectroscopy

This paper describes the band alignment of metal/AlSc(O)N measured using hard X-ray photoelectron spectroscopy. The band offset was determined by using the difference in binding energy from the core level to the upper edge of the VB, and the bandgap was determined from the energy loss spectrum of photoelectrons. The introduction of oxygen into AlScN to make AlScON decreases both the conduction band and VB offsets. The change in barrier height of the metal/AlScN structure is very small relative to the difference in the work function of the metal. This suggests that Fermi-level pinning occurs at the metal/AlScN interface.

The determination of WSe2/GaN heterojunction band offsets in the semipolar (11–22) and nonpolar (11–20) planes by x-ray photoelectron spectroscopy

Wurtzite structured GaN has a severe polarization effect in the c (0001) plane, compared to which the polarization effect is small in the semipolar (11–22) plane, and there is no polarization effect in the nonpolar (11–20) plane GaN. To investigate the influence of the polarization effect on the band bending at the heterojunction interface, we fabricated tungsten diselenide (WSe2)/(0001) GaN, WSe2/(11–22) GaN, and WSe2/(11–20) GaN heterojunctions. We measured the heterojunction valence band offsets (VBOs) by x-ray photoelectron spectroscopy. The VBOs of the three WSe2/GaN heterojunctions were measured to be 2.43 ± 0.15, 2.51 ± 0.15, and 2.23 ± 0.15 eV, and the conduction band offsets were calculated to be 1.11 ± 0.15, 1.19 ± 0.15, and 0.91 ± 0.15 eV, showing the type II energy band alignment of the three heterojunctions. The results demonstrate that WSe2/(11–22) GaN-faced heterojunction band bending is the largest. This provides theoretical insights for two-dimensional WSe2 and three-dimensional semipolar (11–22) GaN and nonpolar (11–20) GaN heterojunction device preparation.

Novel Au/Cu2NiSnS4 Nano-Heterostructure: Synthesis, Structure, Heterojunction Band Offset and Alignment, and Interfacial Charge Transfer Dynamics.

Considering the importance of physics and chemistry at material interfaces, we have explored the coupling of multinary chalcogenide semiconductor Cu2NiSnS4 nanoparticles (CNTS NPs) for the first time with the noble metal (Au) to form Au-CNTS nano-heterostructures (NHSs). The Au-CNTS NHSs is synthesized by a simple facile hot injection method. Synergistic experimental and theoretical approaches are employed to characterize the structural, optical, and electrical properties of the Au-CNTS NHSs. The absorption spectra demonstrate enhanced and broadened optical absorption in the ultraviolet-visible-near-infrared (UV-Vis-NIR) region, which is corroborated by cyclic voltammetry (CV) readings. CV measurements show type II staggered band alignment, with a conduction band offset (CBO) of 0.21 and 0.23 eV at the Au-CNTS/CdS and CNTS/CdS interface, respectively. Complementary first-principles density functional theory (DFT) calculations predict the formation of a stable Au-CNTS NHSs, with the Au nanoparticle transferring its electrons to the CNTS. Moreover, our interface analysis using ultrafast transient absorption experiments demonstrate that the Au-CNTS NHSs facilitates efficient transport and separation of photoexcited charge carriers when compared to pristine CNTS. The transient measurements further reveal a plasmonic electronic transfer from the Au nanoparticle to CNTS. Our advanced analysis and findings will prompt investigations into new functional materials and their photo/electrocatalysis and optoelectronic device applications in the future.