Selenization Conditions Research Articles

Optimization of Selenization Condition for Efficiency CIGSe Solar Cells Based on Postselenization of CuInGa Precursors.

The degree of selenization of the CIGSe absorbers is controlled by regulating the parameters of the selenization reaction. The structure, element distribution, phase composition of the CIGSe absorbers, and the performances of the solar cells with different selenization degrees are studied. Insufficient selenization will lead to residual Cu2Se phase on the surface and insufficient Na diffusion, which will affect the VCu+ on the surface and the recombination at the front interface. However, excessive selenization will make the MoSe2 layer thicken at the back interface of the CIGSe/Mo, resulting in the increase of the series resistance and the enhancement of the recombination at the back interface. The appropriate selenization degree is conducive to inhibiting the recombination at the front and back interfaces. Improved device performances can be obtained by optimizing the selenization degree of the absorbers.

A novel Se-diffused selenization strategy to suppress bulk and interfacial defects in Sb2Se3 thin film solar cell

In recent years, vacuum-based deposition of antimony selenide (Sb2Se3) thin films has garnered significant attention owing to its easy and impurity-free fabrication, along with exceptional power conversion efficiency (PCE). However, the necessary post-selenization process comes with a shortcoming of instigating buried Sb2Se3/molybdenum (Mo) back-contact interface defects. This study introduces a novel Se-diffusion post-selenization technique to precisely regulate the selenium reaction atmosphere, preventing void formation on the Sb2Se3 thin film surface and maintaining film quality for enhanced device efficiency. An optimized selenization condition with a precise Se precursor film thickness led to obtaining highly crystalline, preferentially (hk1) oriented, and large-grained Sb2Se3 films. Furthermore, a meticulous Se diffusion in Sb2Se3 film reduced the inevitable MoSe2 layer thickness at the Mo surface, thereby enhancing the quality of the back contact interface. The Sb2Se3 solar cell that was selenized to optimal level showed significant enhancements, raising the fill factor from 40.06 % to 45.12 % and improving the device efficiency from 2.89 % to 3.57 %. Our newly developed selenization strategy establishes a successful approach to regulate the Sb2Se3 film quality by addressing a crucial challenge in improving the efficiency of antimony chalcogenide solar cells.

Investigating the preparation process of excellent Cu3VSe4 absorption layer prepared by amine-thiol system

Cu3VSe4 material has become a new kind of photovoltaic absorber due to its optical bandgap matching light-absorbing, abundant elements in crust, and high light absorption coefficient. Here, we prepared Cu3VSe4 thin films by amine-thiol method and investigated the preparation process of excellent Cu3VSe4 absorption layer for the first time. The effects of various Cu/V ratios on the morphology, structure, and electrical properties of the films are studied. XRD and Raman results show that pure-phase Cu3VSe4 films are obtained with the Cu/V ratios lower than 2.9. SEM results simply adjusting the Cu/V ratio cannot obtain a compact selenized Cu3VSe4 thin films. The best crystallinity of thin film with 2.8 of Cu/V ratio is named as Cu2.8VSe4 and selected as the representative. Though optimizing the selenization conditions, a dense morphology and good electrical properties of the absorption layer can be prepared under 570 °C of the high-temperature process. Our findings can lay the favorable foundation for high-efficiency Cu3VSe4 devices.

Photoresponse in sequentially stacked antimony selenide thin films

Antimony selenide (Sb2Se3), a binary semiconducting compound has widespread research attention due to its excellent optoelectronic properties in the visible region and usefulness in applications such as solar cells, photosensors and photoelectrodes. The presented study explores the thickness dependent photoresponse in Sb2Se3 thin films, prepared by reactive selenization of antimony films having thickness values of ∼938 nm and ∼1879 nm when stacked second time. Growth orientation along [001] direction was achieved through carefully optimized selenization conditions to enable favourable charge transport in anisotropic Sb2Se3. Predominant Sb2Se3 formation was inferred from x-ray diffraction, Raman spectroscopy, secondary electron microscopy and energy-dispersive X-ray analyses. High optical absorption coefficient values of about 1 × 105 cm−1 and 5.7 × 104 cm−1 were observed for ∼938 nm and ∼1879 nm thick Sb2Se3 thin films. Further, the optoelectronic properties were elucidated through current–voltage and transient photoresponse measurements under dark and illumination conditions. The measurements were done under zero and different bias voltages. Sb2Se3 films having∼ 938 nm thickness exhibited self-driven photoresponse with a responsivity of 4.3×10−8 A W−1 and detectivity of 3.5 × 106 jones respectively, under AM 1.5 G illumination conditions.

Solution-processed Cu3V(S, Se)4 absorbers for thin films solar cells

Cu3V(S, Se)4 material is considered as a novel potential absorber of thin film solar cells due to its excellent properties. In this work, it is the first time that Cu3V(S, Se)4 thin film solar cells are prepared by solution method, and the preparation process of fine absorbers is explored. The combination of air-baking and selenization processes boosts the excellent Cu3V(S, Se)4 absorber. The optimal air-baking and selenization condition is confirmed as 360 °C for 20 min and 560 °C for 30 min, respectively. And the highest photoelectric conversion efficiency (PCE) of Cu3V(S, Se)4 solar cells is 1.68 %. This is the first report on the solution preparation of Cu3V(S, Se)4 thin film solar cells, and it is believed that performance of Cu3V(S, Se)4 solar cells will be optimized by improving the preparation process in the future.

One-step synthesis of two-dimensional PdSe2/PtSe2 heterostructures

Transition metal dichalcogenides (TMDCs) are a type of two-dimensional (2D) layered materials connected by van der Waals forces, laying the foundation for the flexible construction of van der Waals heterostructures (vdWHs). Nevertheless, the main strategies for obtaining vdWHs, such as mechanical exfoliation or co-evaporation, still suffer from small size or non-uniform distribution. This work fabricated the vertically stacked PdSe2/PtSe2 heterostructures via one-step selenization of patterned metal seed layers. And the composition of different heterostructures was experimentally analyzed to determine the optimal selenization conditions for PdSe2/PtSe2 heterostructures. Furthermore, the energy band alignment at the PdSe2/PtSe2 interface was evaluated based on optical absorption spectroscopy (UV–vis) and ultraviolet emission spectroscopy (UPS) analysis. These vertically stacked vdWHs have attracted increasing attention in nano-electronic devices.

A study on Cr incorporation to enhance performance of CZTSSe solar cells via optimizing selenization condition

Annealing Cu2ZnSnS4 (CZTS) precursor films in selenium atmosphere has been demonstrated to be an available means to enhance the quality of Cu2ZnSn(S,Se)4 (CZTSSe) absorber. Therefore, it is important to further explore the selenization conditions during annealing. Herein, Cr-doped CZTSSe absorber was synthesized using solution-processed, and the effects of different selenization conditions on the morphology, structure and photoelectrical performances of Cr-doped CZTSSe thin films were investigated firstly. Research shows that morphology of CCZTSSe films was greatly affected by different selenization conditions. By optimizing the selenization conditions, the crystallinity of CCZTSSe absorber was significantly optimized, and the compactness of the absorber was improved. It was further confirmed that the band gap of CCZTSSe absorber can be adjusted via changing the annealing conditions. The CCZTSSe under the optimum selenization conditions showed a better constituent composition, which further inhibited the harmful defects level of CuZn and [2CuZn + SnZn] in the absorber. Finally, the Cr-doped CZTSSe device at optimum selenidation condition of 520 ℃ for 15 min showed the best conversion efficiency of 5.86 %, in which VOC is 394 mV and FF is 54.07 %, respectively. A new strategy for high efficiency Cr-doped CZTSSe solar cells was proposed by optimizing selenization conditions.

Using soda-lime glass transition temperature to enhance the efficiency of Cu2ZnSn(S,Se)4 solar cell

Homogeneous large-grain structure of Cu2ZnSn(S,Se)4 (CZTSSe) absorber has been proven to be one of the conditions for high photoelectric conversion efficiency (PCE) devices. In this work, we explored that the different choices of selenization temperature had influences on the morphology, crystallinity, and electric properties of CZTSSe absorbers. With the selenization temperature of 540°C, the single-layer large-grain structure of CZTSSe absorber could be prepared, and grain boundary defects could be reduced. 540°C is also the transition temperature of the substrate (Soda-lime glass, SLG) of devices. The SLG softens at the transition temperature and the structure is unstable, resulting in Na entering CZTSSe better at 540°C than at a lower selenization temperature. The suitable Na diffusion can promote the growth of grains and help the corresponding device possesses the highest PCE (9.38%), which is also increased by ∼85% than ones prepared under the lower selenization temperature (PCE stayed at 5%). Therefore, the appropriate selenization conditions for the high-efficiency devices also need to consider the properties of the substrates. These conclusions also propose the new point on obtaining the optimal selenization condition for the high-performance CZTSSe devices.

Impact of Sn4+/Sn2+ ratio in the precursor solution on the performance of CZTSSe solar cell

Precursor design plays an important role in preparing high-quality Cu2ZnSn(S, Se)4 (CZTSSe) absorber layers via solution coating method. In this work, SnCl4 and SnCl2 with different molar ratios were utilized as Sn source in the precursor solution to investigate effects of Sn oxidation state on the film growth process and the related solar cell device performance. Sn4+-rich and Sn2+-rich precursors were found to follow different reaction paths in obtaining CZTSSe grains, thus resulting in quite different crystallinity and morphology of the absorber. For Sn4+-rich precursor system, the direct Se substitution reaction of macroscopically disordered CZTS precursor calls for relatively high temperature to eliminate the double-layer structure and form large-size CZTSSe grains. For Sn2+-dominated precursor solution, however, the reaction of binary compound phases with the catalysis of low-melting-point Sn(S, Se)2 prefers relatively low temperature during the selenization process. The work demonstrates that both types of precursors (or reaction paths) could actually lead to high-quality CZTSSe absorbers and solar cell devices with conversion efficiency higher than 8%, upon the proper selection of selenization conditions.

Optimization of the Selenization Temperature on the Mn-Substituted Cu2ZnSn(S,Se)4 Thin Films and Its Impact on the Performance of Solar Cells.

Cu2ZnSn(S,Se)4 (CZTSSe) films are considered to be promising materials in the advancement of thin-film solar cells. In such films, the amounts of S and Se control the bandgap. Therefore, it is crucial to control the concentration of S/Se to improve efficiency. In this study, Cu2MnxZn1-xSnS4 (CMZTS) films were fabricated using the sol-gel method and treated in a Se environment. The films were post-annealed in a Se atmosphere at various temperature ranges from 300 °C to 550 °C at intervals of 200 °C for 15 min to obtain Cu2MnxZn1-xSn(S,Se)4 (CMZTSSe). The elemental properties, surface morphology, and electro-optical properties of the CMZTSSe films were investigated in detail. The bandgap of the CMZTSSe films was adjustable in the scope of 1.11-1.22 eV. The structural propeties and phase purity of the CMZTSSe films were analyzed by X-ray diffraction and Raman analysis. High-quality CMZTSSe films with large grains could be acquired by suitably changing the selenization temperature. Under the optimized selenization conditions, the efficiency of the fabricated CMZTSSe device reached 3.08%.

Exploring the optimal two-step selenization process to enhance the performance of ionic liquid solution based Cu2ZnSn(S,Se)4 thin film solar cells

Two-step selenization process has been proved to control Cu 2 ZnSn(S,Se) 4 (CZTSSe) crystallization growth, helping to fabricate a homogeneous large-grain structure of CZTSSe absorber. The two-step selenization process is usually composed of the low-temperature nucleation (LT) and high-temperature grain growth reaction (HT) processes. Here, an exploration of optimizing the annealing conditions at each step in the two-step process is reported to obtain the excellent structure of ionic liquid solution based Cu 2 ZnSn(S,Se) 4 absorber, boosting performance of the solar cell. Based on the basic requirement of an absorber candidate for solar cells (the compact films), three effective kinds of two-step process are confirmed (LT400–10&HT540–10, LT400–10&HT550–10, and LT400–10&HT560–10). We further explore the other properties of sample prepared by one-step and these three kinds of two-step process, respectively, and the optimal two-step process can be identified as LT400–10&HT550–10, which also confirms a homogeneous large-grain structure of CZTSSe absorber. Finally, CZTSSe solar cell with the highest efficiency of 9.24% can be achieved, which can be improved 67% than one by one-step annealing process (5.54%). • The detail optimization of annealing conditions at each step in the two-step selenization process is explored. • Homogeneous large-grain structure of Cu 2 ZnSn(S,Se) 4 absorber can be fabricated at the optimal two-step selenization condition. • The best efficiency of corresponding device can be obtained to be 9.24%, increased by 67% compared with one-step process.

Lewis acid etched NixCo1-xSe2 derived from ZIF-L on CoO nanowires for hybrid-supercapacitors

The ideas of high effective specific surface area, multi-component and multi-phase synergistic are introduced to construct high-performance and high-stability electrodes. After etching and exchanging with Lewis acid (nickel ion) and annealing selenization, the hierarchical multi-phase NixCo1-xSe2/carbon–nitrogen frameworks (CNFs, Zeolitic-Imidazolate-Framework-L derivatives) on CoO is synthesized. After systematic research, it is found that the concentration and reaction time of the Lewis acid and selenization conditions can directly affect the structure and composition (bimetal) of the electrode. In the optimal electrode, CNFs with the larger effective specific surface area can fully expose the active material to the electrolyte, the bimetal synergy (Ni-Co), and the multiphase synergy ((Ni, Co)Se2 and CoSe2) can effectively enhance the performance. The anode demonstrates a high mass-specific capacity of 207.8 mAh g−1. A hybrid supercapacitor (NixCo1-xSe2/CNFs/CoO@CC//activated carbon) is fabricated and displayed superior performance and stability: high energy density (45.0 Wh kg−1, 800.0 W kg−1), and a cycle retention rate of 98.0% (12,000 cycles). LEDs in parallel were lit up by the devices, showing their practical value and potential.

ZIFs derived multiphase CoSe2 nanoboxes induced and fixed on CoAl-LDH nanoflowers for high-performance hybrid supercapacitor

Reasonable structures are beneficial to improve the electronic transfer efficiency of the electrode. A novel two/three-dimensional structure with multiphase CoSe2 (M-CoSe2) nanoboxes fixed on CoAl-LDH nanoflowers on carbon paper (CP) is reasonably designed. The formation mechanism of M-CoSe2 is systematically studied through the gradient change of the selenization conditions. Benefitting from the hollow structure of the ZIFs derivatives (carbon-nitrogen frameworks, CNFs), numerous charge transfer channels are provided. Furthermore, M-CoSe2 with enhanced conductivity can furnish abundant active sites and a synergistic effect. The specific capacity of the optimal anode M-CoSe2/CNFs/CoAl-LDO/CP can reach 343.6 mAh g−1 at 1 A g−1, which is equivalent to twice that of the monomer material. The hybrid-supercapacitor (M-CoSe2/CNFs/CoAl-LDO/CP//activated carbon) can provide a high energy density of 50.8 Wh kg−1 at 800 W kg−1, and high stability (capacity loss rate of 3.2%, 10,000 cycles). Besides, LEDs can be lit by HSCs, demonstrating their application potential.

Phase evolution during annealing of low-temperature co-evaporated precursors for CZTSe solar cell absorbers

Systematic investigations into the phase evolution during reactive annealing of copper–zinc–tin–selenide (CZTSe) precursors for the fabrication of kesterite solar cell absorber layers have been paramount in understanding and suppressing the formation of secondary phases that deteriorate device performance. In this study, the phase evolution during annealing of low-temperature co-evaporated CZTSe precursors is investigated. A detailed analysis of films selenized at different temperatures is used to reveal the possible reaction pathway of CZTSe formation. Utilizing a combination of x-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and energy-dispersive x-ray spectroscopy, it is shown that CZTSe formation starts by Cu out-diffusion to the surface and Cu–Se phase formation at a temperature of 350 °C. An intimate mixing of binaries and ternaries during low-temperature selenization is observed. On the contrary, only binaries are observed at high-temperature selenization. This suggests that the CZTSe formation pathway involves reaction schemes where (i) a competition between binary and ternary phases dominates at low-temperature and (ii) binary reactions dominate the process at high temperatures. However, the number of binary phases decreases with increasing selenization temperature until they become undetectable by XRD and Raman spectroscopy at a temperature of 540 °C (selenization time 10 min). Utilizing the presented selenization conditions, prototype solar cells with an efficiency of up to 7.5%, an open-circuit voltage of 407 mV, and a fill factor of 59%, could be demonstrated. The temperature-dependent current density–voltage characteristics indicate that the performance of the prototype devices is limited by bulk Schottky–Read–Hall recombination.

Cu(In,Ga)Se2 thin film solar cells produced by atmospheric selenization of spray casted nanocrystalline layers

Cu(In,Ga)Se2 (CIGS) is suitable absorber material for thin film photovoltaic owing to its excellent thermo-chemical stability and demonstration of high power conversion efficiency of 23.35% for lab-scale devices. The manufacturing of CIGS thin film solar cells need to be economical for commercially viability. Non-vacuum approach for the synthesis of the CIGS thin film absorber is desired for its cost-effective benefits over vacuum based processes. We report development of solution-processed CIGS absorber layer involving spraying of sonochemically prepared nanocrystal ink to obtain pristine CIGS nanocrystal layer, followed by single-step atmospheric pressure selenization utilizing Se pallets as a Se vapor source. Influence of selenization conditions and NaF doping on grain growth of the CIGS thin film absorber is studied in detail by structural, morphological, compositional and electrical characterization. Solar cells prepared under optimized conditions yielded a maximum efficiency of 6.7% without employing any thermal pre-treatment and toxic Potassium Cyanide etching.

Atmospheric Modified Thiol-Based Solution Deposition for Cu2ZnSn(S,Se)4 Absorber Layer

Abandoning the traditional deposition of as-prepared Cu2ZnSnS4 (CZTS) thin films in a glove box, a modified thiol-based solution system suitable for deposition in air is described to further reduce device production costs. In this modified approach, metal salts and thiourea are used as the starting materials and are dissolved in a mixed solution of thioglycolic acid and 2-methoxyethanol, forming a homogeneous precursor solution. The as-deposited CZTS thin films are obtained by spin-coating the precursor solution in air, followed by the selenization process to form large-grained Cu2ZnSn(S,Se)4 thin films. Combining the microstructural results with compositional analyses, the optimal selenization conditions for the Cu2ZnSn(S,Se)4 absorber layer were found to be 540°C and 10 min.

Influence of the selenization condition on the properties of ambient-air processed CZTSSe thin films and device performance

Thoroughly understanding and well controlling the structure and grain growth of Cu2ZnSn(S,Se)4 (CZTSSe) absorber layer in CZTSSe solar cells are essential for getting high power conversion efficiency. Herein, the Cu2ZnSnS4 (CZTS) precursor films were prepared in ambient-air condition by solution method and the effects of selenization condition on the microstructure and device performance are systematically investigated. It is found the heating-up time determines the formation manner of both top large-grained and middle fine-grained layer, while the substrate affects the growth of bottom large-grained layer. A proper heating-up time could effectively optimize the fine-grained layer and achieve better crystallined CZTSSe absorber layer together with a higher device efficiency of 3.38%. A growth mechanism is suggested for the structure formation of CZTSSe.

Porous carbon nanorods decorated with graphitic carbon bubbles encapsulated NiSe nanoparticles as an efficient microwave absorber

Microwave absorbers have been applied extensively to attenuate harmful electromagnetic radiation. In this study, efficient microwave absorbers are successfully prepared using metal-organic frameworks as precursors through a convenient in-situ growth and selenization approach in which NiSe nanoparticles are embedded in rod-like carbon networks decorated with graphitic carbon bubbles. The chemical composition, microstructure, graphitization degree, and corresponding microwave absorption performance are well controlled by changing the selenization condition. Remarkably, the reflection loss of the NiSe/C composite obtained at 700 °C reached −59.70 dB at 7.89 GHz and the effective absorption bandwidth was 4.67 GHz. In the as-prepared composite, pervasive carbon networks help improve conductive loss. The homogeneous interfaces between metal selenides and carbon, as well as the abundant defects and interfaces in the graphitic carbon bubbles, boost interfacial polarization and accelerate electron transfer, contributing to the high-performance absorption.

Investigation on the Selenization Treatment of Kesterite Cu2Mg0.2Zn0.8Sn(S,Se)4 Films for Solar Cell.

High-selenium Cu2Mg0.2Zn0.8Sn(S,Se)4 (CMZTSSe) films were prepared on a soda lime glass substrate using the sol–gel spin coating method, followed by selenization treatment. In this work, we investigated the effects of selenization temperature and selenization time on the crystal quality, and electrical and optical properties of CMZTSSe films. The study on the micro-structure by XRD, Raman, X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDS) analysis showed that all CMZTSSe samples had kesterite crystalline structure. In addition, the crystalline quality of CMZTSSe is improved and larger Se takes the site of S in CMZTSSe with the increase of selenization temperature and selenization time. When increasing the selenization temperature from 500 to 530 °C and increasing the annealing time from 10 to 15 min, the morphological studies showed that the microstructures of the films were dense and void-free. When further increasing the temperature and time, the crystalline quality of the films began to deteriorate. In addition, the bandgaps of CMZTSSe are tuned from 1.06 to 0.93 eV through adjusting the selenization conditions. When CMZTSSe samples are annealed at 530 °C for 15 min under Se atmosphere, the crystal quality and optical–electrical characteristics of CMZTSSe will be optimal, and the grain size and carrier concentration reach maximums of 1.5–2.5 μm and 6.47 × 1018 cm−3.

Growth controlling behavior of vertically aligned MoSe2 film

Vertical layered MoSe2 nanosheets have been synthesized via rapid selenization of a magnetron sputtered Mo film with a large number of penetrating microcracks. The phase microstructure and morphologies of Mo and MoSe2 films were evaluated by X-ray diffractometer, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. The results indicate that a relatively high argon pressure during the sputtering process allows Mo films to deposit with a multi-crack structure. The microcracks increase the inner surface area of Mo films and provide a rapid transmission tunnel for selenium diffusion, which allows MoSe2 nanosheets to grow vertically with a c-axis // substrate texture. The growth mechanism for vertically aligned MoSe2 films has been proposed based on the experimental results. The growth orientation of MoSe2 film can be precisely controlled by adjusting the density of Mo film precursor under the same selenization condition. These findings provide a new strategy for the preparation and application of highly orientated MoSe2 film.