CuInSe2 Research Articles

Optical Applications of CuInSe2 Colloidal Quantum Dots.

The distinctive chemical, physical, electrical, and optical properties of semiconductor quantum dots (QDs) make them a highly fascinating nanomaterial that has been extensively studied. The CuInSe2 (CIS) QDs demonstrates great potential as a nontoxic alternative to CdSe and PbSe QDs for realizing high-performance solution-processed semiconductor devices. The CIS QDs show strong light absorption and bright emission across the visible and infrared spectrum and have been designed to exhibit optical gain. The special characteristics of these properties are of great significance in the fields of solar energy conversion, display, and electronic devices. Here, we present a comprehensive overview of the potential applications of colloidal CIS QDs in various fields, with a particular focus on solar energy conversion (such as QD solar cells, QD-sensitized solar cells, and QD luminescence solar concentrators), solar-to-hydrogen production (such as photocatalytic and photoelectrochemical H2 production), and QD electronics (such as QD transistors, QD light-emitting diodes, and QD photodetectors). Furthermore, we offer our insights into the current challenges and future opportunities associated with CIS QDs for further research.

Crystallization Modulation and Holistic Passivation Enables Efficient Two-Terminal Perovskite/CuIn(Ga)Se2 Tandem Solar Cells

HighlightsIntegrating perovskite solar cells onto irregular rough CuIn(Ga)Se2 (CIGS) surfaces remains a challenge; new strategy was explored to develop monolithic perovskite/CIGS tandem solar cell by manipulating the crystallization of perovskite.Surface reconstruction and field-effect passivation are developed synergistically to issue complex interface relationship between perovskite and C60.The champion power conversion efficiency （PCE） of 24.6% realized, providing significant commercial opportunities for all thin-film-based perovskite/CIGS tandem cells.

Comparative study of the sensitivity of H2S and NO2 in CuInSe2 gas sensors that are fabricated using screen printing and MEMS Integration

This study compares the gas response efficiency of a gas sensor substrate that is produced using screen-printing (SP) and micro-electro-mechanical systems (MEMS) technology, followed by deposition of CuInSe2 (CIS) film layers by radio-frequency (RF) sputtering and hyperthermal annealing for gas sensing applications. The SP substrates are used for CIS film deposition for RF sputtering, followed by various hyperthermal annealing treatments. SEM observations of the CIS film surfaces after annealing show surface particles with a size distribution of 155 to 30 nm, which demonstrate a phenomenon that is similar to Ostwald ripening and which creates structural variation and unevenness after annealing. The CIS film/MEMS substrates (MEMSs) gas sensor substrates are evaluated using a NIR thermal camera to determine the optimal operating temperature for direct annealing, which is 203.2 °C. Gas sensing response tests show that only H2S or NO2 gas rapidly and significantly elicit a response but a CIS film/SPs gas sensor exhibits significant resistance signal noise. The CIS film/MEMSs gas sensor is more stable than CIS film/SPs (after annealing) so it is more suitable for gas sensing. SEM images confirm that the film remains intact, so it is suitable for gas sensing applications.

Real-Time Spectroscopic Ellipsometry for Flux Calibrations in Multi-Source Co-Evaporation of Thin Films: Application to Rate Variations in CuInSe2 Deposition.

Flux calibrations in multi-source thermal co-evaporation of thin films have been developed based on real-time spectroscopic ellipsometry (RTSE) measurements. This methodology has been applied to fabricate CuInSe2 (CIS) thin film photovoltaic (PV) absorbers, as an illustrative example, and their properties as functions of deposition rate have been studied. In this example, multiple Cu layers are deposited step-wise onto the same Si wafer substrate at different Cu evaporation source temperatures (TCu). Multiple In2Se3 layers are deposited similarly at different In source temperatures (TIn). Using RTSE, the Cu and In2Se3 deposition rates are determined as functions of TCu and TIn. These rates, denoted Reff, are measured in terms of effective thickness which is the volume per planar substrate area and accounts for surface roughness variations with deposition time. By assuming that all incident metal atoms are incorporated into the films and that the atomic concentrations in the deposited material components are the same as in single crystals, initial estimates of the Cu and In atom fluxes can be made versus TCu and TIn. Applying these estimates to the co-evaporation of a set of CIS films from individual Cu, In, and Se sources, atomic concentration corrections can be assigned to the Cu and In2Se3 calibration films. The corrections enable generation of a novel calibration diagram predicting the atomic ratio y = [Cu]/[In] and rate Reff within the TCu-TIn plane. Using this diagram, optimization of the CIS properties as a PV absorber can be achieved versus both y and Reff.

Dependence of Crystal‐Field Energy on Strain/Stress Sensed by Temperature Variation of Chalcopyrite Semiconductor (Optical) Band‐Gap for Efficient Band‐Gap Tuning in the CIS/CIGS Photovoltaic

Chalcopyrite selenide single crystals and epitaxial layers (CuIn1−xGaxSe2, x = 0.00, 0.08, 0.19, 1.00) were characterized by temperature‐dependent photoreflectance (PR), photoluminescence (PL), photoluminescence–excitation (PLE), and variable excitation‐energy photoluminescence (VEPL) spectroscopy. The transition energies Ea, Eb, and Ec of both CuInSe2 (CIS) and CuGaSe2 (CGS) layers sensed by PR were higher than the energies of single crystals. CuInSe2 and CuGaSe2 grown on GaAs(001) underlie compressive and tensile stresses, respectively, which lead to band‐gap broadening in CIS and band‐gap narrowing in CGS. The increase of the Ea, Eb, Ec energies of tensely stressed CuGaSe2 layers to energies higher than those of the bulk originates from the stress dependence of the non‐cubic crystal field. Band‐gap scanning of the CuGaSe2 layer with continuous‐wave Ti:sapphire‐laser confirmed the absence of correlation between band‐gap readjustment and intrinsic defects. The energy of the band‐edge exciton EFE, in the PL‐spectra, was lower than the Ea transition energy, in the PR‐spectra, which is assigned to partial quenching of ΔCF with the increase of external tensile stress by gallium‐segregation at the chalcopyrite/GaAs‐interface. The stress dependence of ΔCF is negligible in CuInSe2 and linear, with a rate of 9 meV/100 MPa, in CuGaSe2. It is revealed that the energy band‐gap of photovoltaic chalcopyrite absorbers can be tuned by simultaneous built‐in and external lattice‐tuning.

Study on optoelectronic properties of CuInSe2/CuInSSe films and PN junctions

CuInSe2 (CIS) is a semiconductor with a direct bandgap of about 1.04 eV. Its potential applications in the field of flexible thin-film solar cells are vast and promising. Improving cell performance through the sulfidation of the CIS absorber layer is a vital method. Furthermore, the bandgap can be adjusted through ideal element doping and interfacial state recombination can be decreased. In this study, the mixed source vacuum evaporation is used to prepare CIS, CuInS1.5Se0.5 and CuInS0.5Se1.5 films, followed by annealing under N2, S, and Se atmospheres. Subsequently, Mo/CIS/CdS PN junction and Mo/CuInSxSe2-x (x = 0.5 or 1.5)/CdS PN junctions are fabricated. The results demonstrate that Se-annealing of CIS films reduces hetero-phase formation, improves crystallization quality and yields high intensities of transmittance and reflectance. S-annealing of CISSe films results in enhanced intensities of transmittance and reflectance. The intensities of the primary XRD peaks of CuInS0.5Se1.5 film are greater than those of the CuInS1.5Se0.5 film. The morphologies of the CISSe films become flatter and smoother as annealing in S-atmosphere. The CuInS1.5Se0.5 film shows a higher photocurrent compared to the CuInS0.5Se1.5 film, suggesting that a greater proportion of S can enhance photo carrier concentration of CISSe films. Additionally, the carrier transport in S-annealed CuInS0.5Se1.5/CdS PN junction is predominantly governed by tunneling current mechanism, while carrier transports of other PN junctions are regulated by leakage current mechanism.

Fabrication and Characterization of Electrochemically Deposited CuIn(Ga)Se2 Solar Cells

We have demonstrated a low-cost and simple method for the fabrication of large-area films using the electrodeposition technique. Fairly superior quality CuIn(Ga)Se2 (CIGS) films were deposited by a one-step electrodeposition method using a salt bath followed by annealing in an argon atmosphere at 550 °C for 1 h. The X-ray analyses demonstrate that the films are crystalline in nature, having a chalcopyrite phase. However, the conversion efficiencies are found to be lower compared to other methods. Our results indicate that CIGS films can be produced effectively via a one-step electrodeposition method. The observed morphology can have a great impact on solar cell efficiency. With suitable modifications, this simple and cheaper manufacturing process will be the best alternative method to the vacuum deposition technique for the fabrication of reliable and flexible CIGS solar cells in the near future.

Aluminum‐Based Chalcopyrite Thin Films and Solar Cells

AbstractAluminum‐based chalcopyrite materials have attracted attention because of the wide controllability range of their material properties and potential for use in energy‐conversion devices. Herein, CuAlSe2‐based thin‐film growth and solar cell device properties are discussed. Ternary CuAlSe2 thin films are relatively unstable and decompose weeks after film growth, even when preserved in a dry box. However, alloying with elemental In led to significant improvements in stability. Cu(In,Al)Se2 (CIAS) solar cells yield better photovoltaic performance than CuInSe2 cells, although the effective range of Al concentration that can improve device performance is narrower than that of elemental Ga in Cu(In,Ga)Se2 (CIGS). A decrease in the alkali metal concentration in CIAS films with increasing Al concentration is observed, indicating that the formation energy of alkali‐metal substitutional defects on the Cu site is high, and/or Al‐related complex defects formed are kinetically stable and difficult to replace with alkali metals once they form. Although the direct observation of alkali metals in the bulk (grain interior) of chalcopyrite CuInSe2 and CIGS films has been difficult to date, this result can serve as indirect evidence of the presence of alkali metals in the bulk of CuInSe2 films.

Modeling and efficiency enhancement of SnSe thin film solar cell with a thin CIS layer

Research has been conducted on a solar cell utilizing Tin Selenide (SnSe) as the absorber material having a structure of n-CdS/p-SnSe/p+-CuInSe2/p++-WSe2 with CuInSe2 (CIS) current augmenting and WSe2 back surface field (BSF) layers. The various parameters in CdS, SnSe, CIS, and WSe2 layers have been adjusted methodically for the optimum output. Under the optimum conditions, the proposed n-CdS/p-SnSe solar cell showcases a power conversion efficiency (PCE) of 26.12 % with VOC = 0.788 V, JSC = 38.62 mA/cm2, and FF = 85.78 %. The PCE of the device enhances to 33.88 % with VOC = 1.09 V, JSC = 38.64 mA/cm2, and FF = 80.24 % owing to the incorporation of the WSe2 BSF layer. However, a conjunction of the CIS layer with the SnSe achieves a higher JSC of 42.54 mA/cm2 and a PCE of 36.45 %. These in-depth simulation findings demonstrate the enormous potential of the SnSe absorber with the CIS current boosting layer for the creation of a thin film solar cell that is both affordable and highly efficient.

Synthesis and characterization of CIS/CISe core–shell structured quantum dots in green systems

I–III–VI2 group compounds, such as CuInSe2 (CISe), and CuInS2 (CIS) quantum dots (QDs), are promising for photovoltaic applications by virtue of their excellent photoelectric properties and low toxicity. Considering that the surface of QDs with smaller sizes tends to have a larger density of defect states, inorganic shell layer modification is beneficial to passivate the surface defects and enhance the optical properties and quantum efficiency of QDs. In this study, a novel core–shell structure was constructed by growing a CISe shell layer with a narrower band gap on the surface of CIS nanocrystals with a wider band gap through a green and simple method. The components and properties of the core–shell QDs were analyzed by different characterization methods (XRD, TEM, EDS, UV–Vis, Raman, and fluorescence spectroscopy). The prepared CIS/CISe core–shell QDs with increased size and good coating effects exhibited high absorbance and extended carrier lifetime while showing quantum effects associated with the CISe shell layer, as well as a promising application in the field of solar cells.

Formation, Enhanced Crystallization, Optical Absorption and Electrical Conduction in Copper Indium Selenide Thin Films Prepared via Pulse Laser Welding Technique

AbstractIn this study, thin films of CuInSe2 (CIS) are expeditiously fabricated within 1 s utilizing the pulsed laser welding (PLW) technique. Preceding the PLW process, thin films of InSe (500 nm) are coated with Cu nanosheets of 60 and 120 nm thicknesses using vacuum coating systems. The optimal PLW parameters leading to the formation of CIS films include a pulse width of 1.0 ms, a spot diameter of 2.0 mm, and a repetition frequency of 10 Hz. The resulting CIS films exhibited a well‐crystalline cubic structure with lattice parameters of 5.265 Å. Surface morphology analyses revealed the preferential formation of porous films with varying stoichiometry, a characteristic that can be manipulated by adjusting laser welding parameters. The energy band gap and room temperature electrical conductivity display values of 1.80 eV and 2.06 × 10−5 (Ωcm)−1, respectively. Cu‐rich samples exhibit a wider energy band gap of 1.94 eV and lower electrical conductivity values of 4.78 × 10−7 (Ωcm)−1. The CIS film demonstrates n‐type conductivity attributed to the formation of donor levels centered at 0.24 and 0.10 eV. This study presents an ultrafast method for fabricating CIS films with physical properties compatible with those produced using traditional methods.

Design and Simulation of a High‐Efficiency CuInS2Thin‐Film Solar Cell with a Thin CIS Current Augmenter

Ternary chalcopyrite compound cupper indium disulfide (CuInS2)‐based photovoltaic cells are designed and numerically computed. In this design, n‐CdS and p++‐MoS2have been used as window and back surface field (BSF) layers, respectively. The modeled n‐CdS/p‐CuInS2/p++‐MoS2device provides power conversion efficiency (PCE) of 24.6% withJSCof 26.98 mA cm−2,VOCof 1.05 V, and fill factor (FF) of 86.93%. This efficiency is ≈60% higher the than n‐CdS/p‐CuInS2single heterostructure. Furthermore, the use of a second CuInSe2(CIS) absorber layer between CuInS2absorber and MoS2BSF layer significantly enhances the short‐circuit current. As a result, the current expressively improves to 38.48 mA cm−2, yielding an efficiency of 32.4%. The greater built‐in potential in absorber/BSF interface is attributed to the highJSCandVOC, causing the increment of efficiency. Besides, the photon management by Bragg reflector with 90% back and front reflectance recycling effect further increases the PCE to 36.1%. This work indicates the prospects of CuInS2solar cells with a CuInSe2current augmenter and MoS2BSF layers for the fabrication of efficient CuInS2solar cells.

Enhancing the open-circuit voltage in narrow-bandgap CuInSe2 solar cells via local contact passivation with Al2O3

A fabrication technique using Al2O3-passivated local contacts was employed to produce narrow-bandgap CuInSe2 (CISe) photoabsorbers, which are well-suited as bottom cell materials in tandem devices. However, the performances of CISe cells with narrow bandgaps are impeded by the recombination of charge carriers, which reduces the open-circuit voltage (VOC). To overcome this limitation, an additional Al2O3 passivation layer was added to CISe solar cells. This enhanced the VOC while maintaining a spectral response of up to 1.0 eV, thereby boosting the photovoltaic conversion efficiency of the devices. Further, the Al2O3 passivation layer within the CISe absorber effectively mitigated the recombination of charge carriers, resulting in a substantial improvement in efficiency. Specifically, the Al2O3-passivated local contact hindered the charge-carrier recombination at the rear contact, leading to a marked increase in the VOC. Consequently, the overall photovoltaic conversion efficiency increased significantly from 10.4 % to 13 %. These results are expected to greatly further the development of CISe solar cells and achieve remarkable photovoltaic conversion efficiencies.

Band offsets and point-defect charges of the aluminum and hafnium oxides in contact with the Cu(In,Ga)Se2 chalcopyrite

Surface passivation of CuInSe2 (CIS) and related Cu(In,Ga)Se2 (CIGS) chalcopyrite materials by depositing selected dielectric layers has been a major research activity aiming to reduce interface recombination and increase the electrical efficiency of chalcopyrite-based thin-film solar cells. The present study reports calculations based on density-functional theory and ab-initio thermodynamics that examine the origin of field-effect passivation from alumina and hafnia two wide-gap, predominantly ionic insulators that have exhibited promising passivation qualities in silicon-based microelectronics. The source of fixed charges within the bulk lattices of both oxides was studied by determining the thermodynamically most favorable charge states of their native defects within the admissible ranges of the metal and oxygen chemical potentials. An alignment of the electron bands based on the branch-point energies was performed in order to correctly place the defect charge-transition levels with respect to the band edges of the CIS and the CIGS materials. The trends and predictions of the sign of the fixed charges in either insulator were obtained as a function of temperature, oxygen partial pressure and Fermi-level position inside the band gaps of CIS and CIGS. The findings are discussed in connection with existing experimental studies that extracted the magnitude and polarity of the fixed charges of both alumina and hafnia by analyzing the electrical properties of the CIGS/insulator interfaces.

Inhibiting aluminum oxidation in CuInAl precursor films: Significance for achieving high-performance Cu(InAl)Se2 solar cells

In this work, we demonstrate the effects of aluminum and aluminum oxide within CuInAl precursor films on the formation process of Cu(InAl)Se2 (CIASe) thin films. We carried out a large number of experiments to optimize the conditions for obtaining CIASe thin films with excellent adhesion and electrical properties. Our findings suggest that the fabrication conditions of the precursor films, such as the vacuum level of sputtering chamber and the structure of the precursor films, significantly affect to the growth of the CIASe layer during selenization annealing. Through a series of experiments, we successfully obtained a 2.4 μm-thick CIASe thin film with strong adhesion to the Mo-coated substrate and fabricated a CIASe solar cell with an efficiency of 7.7%. Our study demonstrates the great potential of the two-step fabrication approach for CIASe thin film production, and further improvements are expected by optimizing the fabrication conditions.

Designing CuInSe2 quantum dot-based high-performance Schottky photodetector: a numerical study

Sensing in the near-infrared and visible wavelengths is critically essential for a broad range of potential applications. Colloidal quantum dot(CQD) based photodetectors provide key advantages, such as spectral tuneability, straight integration with electronic parts, high sensitivity and low cost. Here, a Schottky photodiode architecture based on CuInSe2 (CISe) CQDs structure was designed and its photoresponse characteristics were simulated at various absorber layer thicknesses, at different back contact materials, varying light intensities, several defect densities, and different temperatures. A maximum responsivity of about 0.37 A W−1 was recorded from the proposed device. This work demonstrates that CISe CQDs are potential candidate materials for high-performance Schottky photodetectors operating in the near-infrared and visible electromagnetic spectrum.

Control of electronic structure in (Cu, Ag)(Ga, In)Se2 for high efficiency solar cells

A three-dimensional (3D) band-gap energy (E g) map was constructed for a (Cu1−y Ag y )(Ga x In1−x )Se2 (CAGISe) system. This system’s E g increases monotonically from CuInSe2 (CISe) as the ratios of both Ga/(Ga+In) [GGI], x, and Ag/(Cu+Ag) [ACA], y, increase. Furthermore, the energy levels of the VB maximum (VBM) and the conduction band minimum (CBM) were also mapped in 3D. In this CAGISe system, there is no significant change in VBM, whereas CBM does show an increase as the GGI ratio increases. However, as the ACA ratio increases, there is a decrease in VBM level but no significant change in CBM. The substitution effects of Ga for In and Ag for Cu in CISe are discussed on the basis of “principles of orbital interaction.”

Surfactant assisted single step electrodeposition of CuInSe2 thin films with rich indium selenide surface over layer

Abstract In this work, we report on the electrodeposition of CuInSe2 (CIS) thin films with In2Se3 rich surface by a single step deposition technique. It was observed that the In-content deposited in CIS can be improved by the addition of sodium dodecyl sulfate as a surfactant. The presence of an In–Se rich layer was confirmed by electrochemical, compositional and Raman spectroscopy analysis. The photo-electrochemical properties of the as-deposited CuInSe2 thin films were found to be enhanced due to the presence of In–Se rich superficial layer. The presence of an In–Se layer over CIS may act as a p-n homo-junction which may be attributed as the primary reason for the improvement in the PEC properties.

Synthesis and Characterization of CdS/CISe Quantum Dots with Core–Shell Structure

AbstractQuantum dots have received great interest due to their excellent optoelectronic properties. However, the surface defects of quantum dots affect the carrier transport and ultimately reduce the photovoltaic efficiency. In this paper, a core–shell quantum dot by hot‐injection method is prepared to grow a narrow‐band semiconductor layer (CuInSe2 (CISe) quantumdot) on the surface of a broad‐band core material (cadmium sulfide (CdS) nanocrystal). The composition, structure, optical properties, and decay lifetime of CdS/CISe core–shells are investigated in more detail by X‐ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL), UV–vis spectrophotometry, and fluorescence spectroscopy. The CdS/CISe core–shell structure has a broadened absorption range and still shows CISe‐related quantum effects. The increased size of the core–shell and the smaller specific surface area of the CISe shell layer lead to a lower carrier complexation chance, which improves the carrier lifetime.

Unraveling the effects of a GeSe BSF layer on the performance of a CuInSe2 thin film solar cell: a computational analysis

In this work, a dual-heterojunction (DH) thin film solar cell of notable efficiency has been designed and simulated where p-type CuInSe2 (CIS) has been employed as the base layer in combination with an n-type CdS window and a p + -type GeSe back surface field (BSF) layer. The influences of each layer have been revealed using the SCAPS-1D simulator. While the n-CdS/p-CIS single heterojunction (SH) structure acting alone has been found to be resulted with 24.86% of photoconversion efficiency (PCE) with the JSC = 42.80 mA/cm2, VOC = 0.70 V, and FF = 83.44%, an enhancement to PCE of 30.52% is observed with the corresponding JSC of 44.10 mA/cm2, VOC of 0.86 V, and FF of 80.30% owing to the addition of GeSe as BSF layer in the proposed structure with optimized parameters. Because of the enormous built-in potential of the CIS/GeSe interface, increased VOC mostly contributes to the efficiency enhancement. These findings suggest that the CIS absorber layer with GeSe BSF layer is a promising choice for solar energy harvesting in the near future.