In the future, the nanoconfined water monolayer concept may also work for the aligning assembly o... more In the future, the nanoconfined water monolayer concept may also work for the aligning assembly of heterostructures of other types of two-dimensional materials. Indeed, the confinement engineering has provided a universal guideline for designing catalysts, membranes and chemical reactions. First, the synergy of chemical and spatial confinement elevated the secondary battery performances by innovative microstructures and properties. Second, the confinement effect may enhance the supercapacitor performances by the load of redox-active nanowires between MXene nanosheets. Third, the Marangoni effect results in the confinement of carbon nanotubes at MXene interfaces, which compose a fast-response humidity sensor. More interesting behaviors could be expected after improving the in-plane alignment of the heterostructures of 2D materials, which may exhibit enhanced magnetic and half-metallic properties as well as enhanced proton and spin-transport performances.
Flexible electronics has emerged as a continuously growing field of study. Two-dimensional (2D) m... more Flexible electronics has emerged as a continuously growing field of study. Two-dimensional (2D) materials often act as conductors and electrodes in electronic devices, holding significant promise in the design of high-performance, flexible electronics. Numerous studies have focused on harnessing the potential of these materials for the development of such devices. However, to date, the incorporation of 2D materials in flexible electronics has rarely been summarized or reviewed. Consequently, there is an urgent need to develop comprehensive reviews for rapid updates on this evolving landscape. This review Chongyang Hou, Shuye Zhang, and Rui Liu contributed equally to this study.
Three-dimensional (3D) graphene with a high specific surface area and excellent electrical conduc... more Three-dimensional (3D) graphene with a high specific surface area and excellent electrical conductivity holds extraordinary potential for molecular gas sensing. Gas molecules adsorbed onto graphene serve as electron donors, leading to an increase in conductivity. However, several challenges remain for 3D graphene-based gas sensors, such as slow response and long recovery time. Therefore, research interest remains in the promotion of the sensitivity of molecular gas detection. In this study, we fabricate oxygen plasma-treated 3D graphene for the high-performance gas sensing of formaldehyde. We synthesize large-area, high-quality, 3D graphene over Ni foam by chemical vapor deposition and obtain freestanding 3D graphene foam after Ni etching. We compare three types of strategies—non-treatment, oxygen plasma, and etching in HNO3 solution—for the posttreatment of 3D graphene. Eventually, the strategy for oxygen plasma-treated 3D graphene exceeds expectations, which may highlight the general gas sensing based on chemiresistors.
ABSTRACT One of the more common routes to fabricate graphene is by chemical vapor deposition (CVD... more ABSTRACT One of the more common routes to fabricate graphene is by chemical vapor deposition (CVD). This is primarily because of its potential to scale up the process and produce large area graphene. For the synthesis of large area monolayer Cu is probably the most popular substrate since it has a low carbon solubility enabling homogenous single-layer sheets of graphene to form. This process requires a very clean substrate. In this work we look at the efficiency of common pre-treatments such as etching or wiping with solvents and compare them to an oxidation treatment at 1025 oC followed by a reducing process by annealing in H2. The oxidation/reduction process is shown to be far more efficient allowing large area homogeneous single layer graphene formation without the presence of additional graphene flakes which form from organic contamination on the Cu surface.
Graphene remains of great interest in biomedical applications because of biocompatibility. Diseas... more Graphene remains of great interest in biomedical applications because of biocompatibility. Diseases relating to human senses interfere with life satisfaction and happiness. Therefore, the restoration by artificial organs or sensory devices may bring a bright future by the recovery of senses in patients. In this review, we update the most recent progress in graphene based sensors for mimicking human senses such as artificial retina for image sensors, artificial eardrums, gas sensors, chemical sensors, and tactile sensors. The brain-like processors are discussed based on conventional transistors as well as memristor related neuromorphic computing. The brain–machine interface is introduced for providing a single pathway. Besides, the artificial muscles based on graphene are summarized in the means of actuators in order to react to the physical world. Future opportunities remain for elevating the performances of human-like sensors and their clinical applications.
In view of the long-standing controversy over the reversibility of transition metals in Sn-based ... more In view of the long-standing controversy over the reversibility of transition metals in Sn-based alloys as an anode for Li-ion batteries, an in situ real-time magnetic monitoring method was used to investigate the evolution of Sn–Co alloy during the electrochemical cycling. Sn–Co alloy film anodes with different compositions were prepared via magnetron sputtering without using binders and conductive additives. The magnetic responses showed that the Co particles liberated by Li insertion recombine fully with Sn during the delithiation to reform Sn–Co alloy into stannum-richer phases Sn7Co3. However, as the Co content increases, it can only recombine partially with Sn into cobalt-richer phases Sn3Co7. The unconverted Co particles may form a dense barrier layer and prevent the full reaction of Li with all the Sn in the anode, leading to lower capacities. In addition, we also showed that the Fe can recombine with Sn (Sb) during the delithiation in the Sn (Sb)–Fe alloy film anodes by operando magnetometry. These critical results shed light on understanding the reaction mechanism of transition metals and provide valuable insights toward the design of high-performance Sn (Sb)-based alloy anodes.
Graphene‐Based Nerve Scaffold with Endogenous Electrical Signals In the Three Kingdoms Period of ... more Graphene‐Based Nerve Scaffold with Endogenous Electrical Signals In the Three Kingdoms Period of ancient China, the chief minister of the Shu Kingdom borrowed arrows with thatched boats from the enemy country. In article number 2104424, Chunhui Sun, Ning Meng, Lin Han, Hong Liu, and co‐workers introduce wireless electrical stimuli using graphene as generator under rotating magnetic field, to direct adipose‐derived mesenchymal stem cells (ADMSCs) to differentiate into functional neurons. This safe magnetoelectricity conversion provides localized electrical stimulation for potential neurodegenerative therapy.
Antimony selenide (Sb2Se3) has rapidly emerged in the field of photovoltaics with one-dimensional... more Antimony selenide (Sb2Se3) has rapidly emerged in the field of photovoltaics with one-dimensional crystal structure. However, the power conversion efficiency (PCE) of Sb2Se3 solar cells is influenced by the orientation of the Sb2Se3 photoactive layers. In this study, we investigate the influence of substrate properties on the preferred orientation and microstructure of Sb2Se3 films systematically. With the rise of substrate surface temperature and the decline of substrate surface bonding energy, the preferred orientation of the Sb2Se3 films altered from (hk0) to (hk1) and finally to (002). After summarizing the performance of different preferentially oriented Sb2Se3 solar cells, the results showed that the (hk0)-preferentially oriented devices exhibited a poor performance of less than 1.1%. As the preferred orientation of Sb2Se3 absorbers changed from (hk0) to (hk1), the carrier transport changed from inter-ribbon charge hopping to transportation along the (Sb4Se6)n ribbons. This enhanced the carrier transport efficiency, thereby leading to the enhancement of the PCE to 2%–3%. Furthermore, when the (002) texture coefficient (TC) of the Sb2Se3 films was between 1.8 and 3.6, the PCE of the devices was further enhanced to above 3.5%. A maximum PCE of 4.79% can be obtained when the (002) TC was 3.24. This study reveals the relationship between the Sb2Se3 film preferred orientation and device performance, and demonstrates an effective way to precisely control the Sb2Se3 film microstructure to obtain a high PCE.
The Internet of Things era has promoted enormous research on sensors, communications, data fusion... more The Internet of Things era has promoted enormous research on sensors, communications, data fusion, and actuators. Among them, sensors are a prerequisite for acquiring the environmental information for delivering to an artificial data center to make decisions. The MXene‐based sensors have aroused tremendous interest because of their extraordinary performances. In this review, the electrical, electronic, and optical properties of MXenes are first introduced. Next, the MXene‐based sensors are discussed according to the sensing mechanisms such as electronic, electrochemical, and optical methods. Initially, biosensors are introduced based on chemiresistors and field‐effect transistors. Besides, the wearable pressure sensor is demonstrated with piezoresistive devices. Third, the electrochemical methods include amperometry and electrochemiluminescence as examples. In addition, the optical approaches refer to surface plasmonic resonance and fluorescence resonance energy transfer. Moreover, the prospects are delivered of multimodal data fusion toward complicated human‐like senses. Eventually, future opportunities for MXene research are conveyed in the new material discovery, structure design, and proof‐of‐concept devices.
Abstract PtSx, as a more recent 2D material that aroused extensive research interests, has been a... more Abstract PtSx, as a more recent 2D material that aroused extensive research interests, has been applied in electronic and optoelectronic devices because of its excellent electronic characteristics and commendable stability. However, the synthesis of large-scale uniform PtSx remains a challenge. Here we studied a modified chemical vapor deposition (CVD) method to grow large-scale uniform PtSx films on SiO2/Si and c-plane sapphire substrates, which can avoid some disadvantages of the mechanical exfoliation method in the device fabrication. The large area uniform PtSx films are achieved through Pt sulfurization using H2S gas, replacing the sulfur powder in traditional methods, as the sulfur source. The material characterizations successfully proved that our modified CVD method is feasible and repeatable, and the PtSx film can be synthesized on different substrates. The PtSx photodevices show good photoresponse properties with a wide spectrum response range. The PtSx/sapphire device shows a better photoresponse in terms of the detectivity (9.17 × 109 Jones) and the responsivity (0.31 A W−1) than that of the PtSx/SiO2/Si device in our experiment, as well as one-year air stability, which may be caused by the different PtSx film quality due to a lattice mismatch difference between the PtSx and the different substrates. The results offer the design and synthesis technology for large-scale, uniform, and stable PtSx film, as well as an example of photoresponse-enhanced devices which could be generalizable to other transition metal dichalcogenides (TMDCs) and devices for future development and applications.
A facile metal sulfurization was employed for preparing a 4-inch wafer scale PtS film. The 2D PtS... more A facile metal sulfurization was employed for preparing a 4-inch wafer scale PtS film. The 2D PtS nonlayered material were studied by STEM, SAED, XPS and Raman spectra. The formation of PtS (other than PtS2) was interpreted by the phase diagram.
Advancing the lithium-ion battery technology requires the understanding of electrochemical proces... more Advancing the lithium-ion battery technology requires the understanding of electrochemical processes in electrode materials with high resolution, accuracy, and sensitivity. However, most techniques today are limited by their inability to separate the complex signals from slurry-coated composite electrodes. Here, we use a three-dimensional “Swiss-roll” microtubular electrode that is incorporated into a micrometer-sized lithium battery. This on-chip platform combines various in situ characterization techniques and precisely probes the intrinsic electrochemical properties of each active material due to the removal of unnecessary binders and additives. As an example, it helps elucidate the critical role of Fe substitution in a conversion-type NiO electrode by monitoring the evolution of Fe 2 O 3 and solid electrolyte interphase layer. The markedly enhanced electrode performances are therefore explained. Our approach exposes a hitherto unexplored route to tracking the phase, morphology, ...
In the future, the nanoconfined water monolayer concept may also work for the aligning assembly o... more In the future, the nanoconfined water monolayer concept may also work for the aligning assembly of heterostructures of other types of two-dimensional materials. Indeed, the confinement engineering has provided a universal guideline for designing catalysts, membranes and chemical reactions. First, the synergy of chemical and spatial confinement elevated the secondary battery performances by innovative microstructures and properties. Second, the confinement effect may enhance the supercapacitor performances by the load of redox-active nanowires between MXene nanosheets. Third, the Marangoni effect results in the confinement of carbon nanotubes at MXene interfaces, which compose a fast-response humidity sensor. More interesting behaviors could be expected after improving the in-plane alignment of the heterostructures of 2D materials, which may exhibit enhanced magnetic and half-metallic properties as well as enhanced proton and spin-transport performances.
Flexible electronics has emerged as a continuously growing field of study. Two-dimensional (2D) m... more Flexible electronics has emerged as a continuously growing field of study. Two-dimensional (2D) materials often act as conductors and electrodes in electronic devices, holding significant promise in the design of high-performance, flexible electronics. Numerous studies have focused on harnessing the potential of these materials for the development of such devices. However, to date, the incorporation of 2D materials in flexible electronics has rarely been summarized or reviewed. Consequently, there is an urgent need to develop comprehensive reviews for rapid updates on this evolving landscape. This review Chongyang Hou, Shuye Zhang, and Rui Liu contributed equally to this study.
Three-dimensional (3D) graphene with a high specific surface area and excellent electrical conduc... more Three-dimensional (3D) graphene with a high specific surface area and excellent electrical conductivity holds extraordinary potential for molecular gas sensing. Gas molecules adsorbed onto graphene serve as electron donors, leading to an increase in conductivity. However, several challenges remain for 3D graphene-based gas sensors, such as slow response and long recovery time. Therefore, research interest remains in the promotion of the sensitivity of molecular gas detection. In this study, we fabricate oxygen plasma-treated 3D graphene for the high-performance gas sensing of formaldehyde. We synthesize large-area, high-quality, 3D graphene over Ni foam by chemical vapor deposition and obtain freestanding 3D graphene foam after Ni etching. We compare three types of strategies—non-treatment, oxygen plasma, and etching in HNO3 solution—for the posttreatment of 3D graphene. Eventually, the strategy for oxygen plasma-treated 3D graphene exceeds expectations, which may highlight the general gas sensing based on chemiresistors.
ABSTRACT One of the more common routes to fabricate graphene is by chemical vapor deposition (CVD... more ABSTRACT One of the more common routes to fabricate graphene is by chemical vapor deposition (CVD). This is primarily because of its potential to scale up the process and produce large area graphene. For the synthesis of large area monolayer Cu is probably the most popular substrate since it has a low carbon solubility enabling homogenous single-layer sheets of graphene to form. This process requires a very clean substrate. In this work we look at the efficiency of common pre-treatments such as etching or wiping with solvents and compare them to an oxidation treatment at 1025 oC followed by a reducing process by annealing in H2. The oxidation/reduction process is shown to be far more efficient allowing large area homogeneous single layer graphene formation without the presence of additional graphene flakes which form from organic contamination on the Cu surface.
Graphene remains of great interest in biomedical applications because of biocompatibility. Diseas... more Graphene remains of great interest in biomedical applications because of biocompatibility. Diseases relating to human senses interfere with life satisfaction and happiness. Therefore, the restoration by artificial organs or sensory devices may bring a bright future by the recovery of senses in patients. In this review, we update the most recent progress in graphene based sensors for mimicking human senses such as artificial retina for image sensors, artificial eardrums, gas sensors, chemical sensors, and tactile sensors. The brain-like processors are discussed based on conventional transistors as well as memristor related neuromorphic computing. The brain–machine interface is introduced for providing a single pathway. Besides, the artificial muscles based on graphene are summarized in the means of actuators in order to react to the physical world. Future opportunities remain for elevating the performances of human-like sensors and their clinical applications.
In view of the long-standing controversy over the reversibility of transition metals in Sn-based ... more In view of the long-standing controversy over the reversibility of transition metals in Sn-based alloys as an anode for Li-ion batteries, an in situ real-time magnetic monitoring method was used to investigate the evolution of Sn–Co alloy during the electrochemical cycling. Sn–Co alloy film anodes with different compositions were prepared via magnetron sputtering without using binders and conductive additives. The magnetic responses showed that the Co particles liberated by Li insertion recombine fully with Sn during the delithiation to reform Sn–Co alloy into stannum-richer phases Sn7Co3. However, as the Co content increases, it can only recombine partially with Sn into cobalt-richer phases Sn3Co7. The unconverted Co particles may form a dense barrier layer and prevent the full reaction of Li with all the Sn in the anode, leading to lower capacities. In addition, we also showed that the Fe can recombine with Sn (Sb) during the delithiation in the Sn (Sb)–Fe alloy film anodes by operando magnetometry. These critical results shed light on understanding the reaction mechanism of transition metals and provide valuable insights toward the design of high-performance Sn (Sb)-based alloy anodes.
Graphene‐Based Nerve Scaffold with Endogenous Electrical Signals In the Three Kingdoms Period of ... more Graphene‐Based Nerve Scaffold with Endogenous Electrical Signals In the Three Kingdoms Period of ancient China, the chief minister of the Shu Kingdom borrowed arrows with thatched boats from the enemy country. In article number 2104424, Chunhui Sun, Ning Meng, Lin Han, Hong Liu, and co‐workers introduce wireless electrical stimuli using graphene as generator under rotating magnetic field, to direct adipose‐derived mesenchymal stem cells (ADMSCs) to differentiate into functional neurons. This safe magnetoelectricity conversion provides localized electrical stimulation for potential neurodegenerative therapy.
Antimony selenide (Sb2Se3) has rapidly emerged in the field of photovoltaics with one-dimensional... more Antimony selenide (Sb2Se3) has rapidly emerged in the field of photovoltaics with one-dimensional crystal structure. However, the power conversion efficiency (PCE) of Sb2Se3 solar cells is influenced by the orientation of the Sb2Se3 photoactive layers. In this study, we investigate the influence of substrate properties on the preferred orientation and microstructure of Sb2Se3 films systematically. With the rise of substrate surface temperature and the decline of substrate surface bonding energy, the preferred orientation of the Sb2Se3 films altered from (hk0) to (hk1) and finally to (002). After summarizing the performance of different preferentially oriented Sb2Se3 solar cells, the results showed that the (hk0)-preferentially oriented devices exhibited a poor performance of less than 1.1%. As the preferred orientation of Sb2Se3 absorbers changed from (hk0) to (hk1), the carrier transport changed from inter-ribbon charge hopping to transportation along the (Sb4Se6)n ribbons. This enhanced the carrier transport efficiency, thereby leading to the enhancement of the PCE to 2%–3%. Furthermore, when the (002) texture coefficient (TC) of the Sb2Se3 films was between 1.8 and 3.6, the PCE of the devices was further enhanced to above 3.5%. A maximum PCE of 4.79% can be obtained when the (002) TC was 3.24. This study reveals the relationship between the Sb2Se3 film preferred orientation and device performance, and demonstrates an effective way to precisely control the Sb2Se3 film microstructure to obtain a high PCE.
The Internet of Things era has promoted enormous research on sensors, communications, data fusion... more The Internet of Things era has promoted enormous research on sensors, communications, data fusion, and actuators. Among them, sensors are a prerequisite for acquiring the environmental information for delivering to an artificial data center to make decisions. The MXene‐based sensors have aroused tremendous interest because of their extraordinary performances. In this review, the electrical, electronic, and optical properties of MXenes are first introduced. Next, the MXene‐based sensors are discussed according to the sensing mechanisms such as electronic, electrochemical, and optical methods. Initially, biosensors are introduced based on chemiresistors and field‐effect transistors. Besides, the wearable pressure sensor is demonstrated with piezoresistive devices. Third, the electrochemical methods include amperometry and electrochemiluminescence as examples. In addition, the optical approaches refer to surface plasmonic resonance and fluorescence resonance energy transfer. Moreover, the prospects are delivered of multimodal data fusion toward complicated human‐like senses. Eventually, future opportunities for MXene research are conveyed in the new material discovery, structure design, and proof‐of‐concept devices.
Abstract PtSx, as a more recent 2D material that aroused extensive research interests, has been a... more Abstract PtSx, as a more recent 2D material that aroused extensive research interests, has been applied in electronic and optoelectronic devices because of its excellent electronic characteristics and commendable stability. However, the synthesis of large-scale uniform PtSx remains a challenge. Here we studied a modified chemical vapor deposition (CVD) method to grow large-scale uniform PtSx films on SiO2/Si and c-plane sapphire substrates, which can avoid some disadvantages of the mechanical exfoliation method in the device fabrication. The large area uniform PtSx films are achieved through Pt sulfurization using H2S gas, replacing the sulfur powder in traditional methods, as the sulfur source. The material characterizations successfully proved that our modified CVD method is feasible and repeatable, and the PtSx film can be synthesized on different substrates. The PtSx photodevices show good photoresponse properties with a wide spectrum response range. The PtSx/sapphire device shows a better photoresponse in terms of the detectivity (9.17 × 109 Jones) and the responsivity (0.31 A W−1) than that of the PtSx/SiO2/Si device in our experiment, as well as one-year air stability, which may be caused by the different PtSx film quality due to a lattice mismatch difference between the PtSx and the different substrates. The results offer the design and synthesis technology for large-scale, uniform, and stable PtSx film, as well as an example of photoresponse-enhanced devices which could be generalizable to other transition metal dichalcogenides (TMDCs) and devices for future development and applications.
A facile metal sulfurization was employed for preparing a 4-inch wafer scale PtS film. The 2D PtS... more A facile metal sulfurization was employed for preparing a 4-inch wafer scale PtS film. The 2D PtS nonlayered material were studied by STEM, SAED, XPS and Raman spectra. The formation of PtS (other than PtS2) was interpreted by the phase diagram.
Advancing the lithium-ion battery technology requires the understanding of electrochemical proces... more Advancing the lithium-ion battery technology requires the understanding of electrochemical processes in electrode materials with high resolution, accuracy, and sensitivity. However, most techniques today are limited by their inability to separate the complex signals from slurry-coated composite electrodes. Here, we use a three-dimensional “Swiss-roll” microtubular electrode that is incorporated into a micrometer-sized lithium battery. This on-chip platform combines various in situ characterization techniques and precisely probes the intrinsic electrochemical properties of each active material due to the removal of unnecessary binders and additives. As an example, it helps elucidate the critical role of Fe substitution in a conversion-type NiO electrode by monitoring the evolution of Fe 2 O 3 and solid electrolyte interphase layer. The markedly enhanced electrode performances are therefore explained. Our approach exposes a hitherto unexplored route to tracking the phase, morphology, ...
In the course of the PhD thesis large area homogeneous strictly monolayer graphene films were suc... more In the course of the PhD thesis large area homogeneous strictly monolayer graphene films were successfully synthesized with chemical vapor deposition over both Cu and Si (with surface oxide) substrates. These synthetic graphene films were characterized with thorough microscopic and spectrometric tools and also in terms of electrical device performance. Graphene growth with a simple chemo thermal route was also explored for understanding the growth mechanisms.
The formation of homogeneous graphene film over Cu requires a clean substrate. For this reason, a study has been conducted to determine the extent to which various pre-treatments may be used to clean the substrate. Four type of pre-treatments on Cu substrates are investigated, including wiping with organic solvents, etching with ferric chloride solution, annealing in air for oxidation, and air annealing with post hydrogen reduction. Of all the pretreatments, air oxidation with post hydrogen annealing is found to be most efficient at cleaning surface contaminants and thus allowing for the formation of large area homogeneous strictly monolayer graphene film over Cu substrate.
Chemical vapor deposition is the most generally used method for graphene mass production and integration. There is also interest in growing graphene directly from organic molecular adsorbents on a substrate. Few studies exist. These procedures require multiple step reactions, and the graphene quality is limited due to small grain sizes. Therefore, a significantly simple route has been demonstrated. This involves organic solvent molecules adsorbed on a Cu surface, which is then annealed in a hydrogen atmosphere in order to ensure direct formation of graphene on a clean Cu substrate. The influence of temperature, pressure and gas flow rate on the one-step chemo thermal synthesis route has been investigated systematically. The temperature-dependent study provides an insight into the growth kinetics, and supplies thermodynamic information such as the activation energy, Ea, for graphene synthesis from acetone, isopropanol and ethanol. Also, these studies highlight the role of hydrogen radicals for graphene formation. In addition, an improved understanding of the role of hydrogen is also provided in terms of graphene formation from adsorbed organic solvents (e.g., in comparison to conventional thermal chemical vapor deposition).
Graphene synthesis with chemical vapor deposition directly over Si wafer with surface oxide (Si/SiOx ) has proven challenging in terms of large area and uniform layer number. The direct growth of graphene over Si/SiO x substrate becomes attractive because it is free of an undesirable transfer procedure, necessity for synthesis over metal substrate, which causes breakage, contamination and time consumption. To obtain homogeneous graphene growth, a local equilibrium chemical environment has been established with a facile confinement CVD approach, inwhich two Si wafers with their oxide faces in contact to form uniform monolayer graphene. A thorough examination of the material reveals it comprises facetted grains despite initially nucleating as round islands. Upon clustering these grains facet to minimize their energy, which leads to faceting in polygonal forms because the system tends to ideally form hexagons (the lowest energy form). This is much like the hexagonal cells in a beehive honeycomb which require the minimum wax. This process also results in a near minimal total grain boundary length per unit area. This fact, along with the high quality of the resultant graphene is reflected in its electrical performance which is highly comparable with graphene formed over other substrates, including Cu. In addition the graphene growth is self-terminating, which enables the wide parameter window for easy control.
This chemical vapor deposition approach is easily scalable and will make graphene formation directly on Si wafers competitive against that from metal substrates which suffer from transfer. Moreover, this growth path shall be applicable for direct synthesis of other two dimensional materials and their Van der Waals hetero-structures.
Bifacial Cu(In,Ga)Se 2 thin film solar cell could be widely used as solar windows
in bus shelter,... more Bifacial Cu(In,Ga)Se 2 thin film solar cell could be widely used as solar windows in bus shelter, railway station and airport waiting hall due to its semi-transparency with transparent conducting oxide as back electrode. Meanwhile, it is suitable in tandem solar cells. However, the rectifying junction between transparent conducting oxide and Cu(In,Ga)Se 2 absorbers deteriorates the cell performance. Thus, the contact issue of ZnO:Ga and Cu(In,Ga)Se 2 were analyzed and solved in this thesis. Bifacial CIGS solar cells were fabricated with ZnO:Ga/ MoSe 2 back electrode. To begin with, the history of energy exploits and solar cells, the development milestones of Cu(In,Ga)Se 2 solar cells are listed in the first chapter. Following is detailed information of bifacial CIGS solar cells. And then, the device structure of bifacial solar cells and the deposition process for each layer are simplified together with the characterization methods. Thereafter, the selenization parameters of Mo thin films both on bare soda lime glass and on ZnO:Ga coated one were exploited and optimized, i.e. the substrate temperature and the sodium incorporation. The addition of MoSe 2 into ZnO:Ga/ CIGS interface and its effect on the contact were studied. Finally, CIGS solar cells were fabricated on both ZnO:Ga electrodes and ZnO:Ga/ MoSe 2 back contact. Cell performances were carried on under the illumination of AM 1.5 sun simulator. Quantum efficiencies were also measured with crystal silicon solar cells as references. Further modification for solar cells are delivered with comparison and analysis of parameters related to improving current solar cells. Key Words: transparent conducting oxide, bifacial solar cells, MoSe2, CIGS thin film, ZnO:Ga
The 2D materials and their stacking heterostructures have inspired enormous interests due to thei... more The 2D materials and their stacking heterostructures have inspired enormous interests due to their extraordinary physical properties. WSe2, as a p-type semiconductor, represents a foremost building block in the p-n junctions. WSe2 shall possesses the features of large area, homogeneity and precise layer control. To date, there is yet an ideal synthesis method ever reported. Here, we present a facile approach to prepare high-quality large-area homogenous WSe2 full films. In brief, we developed a pre-seeding strategy for depositing W-containing precursors over dielectric substrates, which form well-distributed particles as seeding center. Upon the salt-assisted sublimation of tungsten oxides, the WSe2 forms over the seeded substrates (at high temperature) in the Se-rich atmosphere. Eventually, the high quality of the synthetic film has been reflected on the high performances of photodetectors and field-effect transistors. Our finding may pave the way of sub-1 cm scale growth of transition metal dichalcogenides, which are ideal starting materials for the integrated flexible electronics. In future, we may apply this strategy to the synthesis of layered noble metal dichalcogenides (such as PdSe2).
Keywords: transition metal dichalcogenides; WSe2; optoelectronics; photodetectors; transistors; layered noble metal dichalcogenides
Na incorporation into Cu(In,Ga)Se 2 (CIGS) thin films deposited on flexible polyimide (PI) substr... more Na incorporation into Cu(In,Ga)Se 2 (CIGS) thin films deposited on flexible polyimide (PI) substrate leads to a great improvement in the properties of CIGS. In this work, we discuss the influence of different Na incorporation methods on CIGS. The XRD patterns and Hall measurements show that the interdiffusion of In-Ga is restrained and the Ga content is higher in the surface layer of the CIGS film, which exhibits double-peak reflection pattern. This is caused by the deposition of a NaF precursor method, whereas the improving effect is found in the films prepared by the post deposition of NaF method.
the chalcopyrite CIGS semiconductor thin film deposited by low-temperature three-stage co-evapora... more the chalcopyrite CIGS semiconductor thin film deposited by low-temperature three-stage co-evaporation process. In the first stage, the substrate temperature is 350 o C, subsequently the substrate temperature is kept on 450 o C in second and third stages. The configuration of CIGS thin film-based solar cell is as SLG/Mo/CIGS/CdS/ZnO/ZnO:Al/Ni-Al. grid, and the heterojunction is formed between P type CIGS and N type CdS. In our work, the temperature-dependent current-voltage (JVT) measurements on CIGS solar cells are investigated. The active energy is extracted from JVT measurement data. Simultaneously, the ideality factors in different temperature are fitted by tunneling enhanced recombination models, which can deduce the characteristic tunneling energy and characteristic energy of defect distribution. Finally, the dominated recombination mechanisms and paths is determined。 This result is helpful to further understand the electrical transport of this device. Key words: solar cells, CIGS thin film absorber, recombination paths
the chalcopyrite CIGS semiconductor thin film deposited by low-temperature three-stage co-evapora... more the chalcopyrite CIGS semiconductor thin film deposited by low-temperature three-stage co-evaporation process. In the first stage, the substrate temperature is 350 o C, subsequently the substrate temperature is kept on 450 o C in second and third stages. The configuration of CIGS thin film-based solar cell is as SLG/Mo/CIGS/CdS/ZnO/ZnO:Al/Ni-Al. grid, and the heterojunction is formed between P type CIGS and N type CdS. In our work, the temperature-dependent current-voltage (JVT) measurements on CIGS solar cells are investigated. The active energy is extracted from JVT measurement data. Simultaneously, the ideality factors in different temperature are fitted by tunneling enhanced recombination models, which can deduce the characteristic tunneling energy and characteristic energy of defect distribution. Finally, the dominated recombination mechanisms and paths is determined。 This result is helpful to further understand the electrical transport of this device.
Na incorporation into Cu(In,Ga)Se 2 (CIGS) thin films deposited on flexible polyimide (PI) substr... more Na incorporation into Cu(In,Ga)Se 2 (CIGS) thin films deposited on flexible polyimide (PI) substrate leads to a great improvement in the properties of CIGS. In this work, we discuss the influence of different Na incorporation methods on CIGS. The XRD patterns and Hall measurements show that the interdiffusion of In-Ga is restrained and the Ga content is higher in the surface layer of the CIGS film, which exhibits double-peak reflection pattern. This is caused by the deposition of a NaF precursor method, whereas the improving effect is found in the films prepared by the post deposition of NaF method.
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Papers by Jinbo Pang
The formation of homogeneous graphene film over Cu requires a clean substrate. For this reason, a study has been conducted to determine the extent to which various pre-treatments may be used to clean the substrate. Four type of pre-treatments on Cu substrates are investigated, including wiping with organic solvents, etching with ferric chloride solution, annealing in air for oxidation, and air annealing with post hydrogen reduction. Of all the pretreatments, air oxidation with post hydrogen annealing is found to be most efficient at cleaning surface contaminants and thus allowing for the formation of large area homogeneous strictly monolayer graphene film over Cu substrate.
Chemical vapor deposition is the most generally used method for graphene mass production and integration. There is also interest in growing graphene directly from organic molecular adsorbents on a substrate. Few studies exist. These procedures require multiple step reactions, and the graphene quality is limited due to small grain sizes. Therefore, a significantly simple route has been demonstrated. This involves organic solvent molecules adsorbed on a Cu surface, which is then annealed in a hydrogen atmosphere in order to ensure direct formation of graphene on a clean Cu substrate. The influence of temperature, pressure and gas flow rate on the one-step chemo thermal synthesis route has been investigated systematically. The temperature-dependent study provides an insight into the growth kinetics, and supplies thermodynamic information such as the activation energy, Ea, for graphene synthesis from acetone, isopropanol and ethanol. Also, these studies highlight the role of hydrogen radicals for graphene formation. In addition, an improved understanding of the role of hydrogen is also provided in terms of graphene formation from adsorbed organic solvents (e.g., in comparison to conventional thermal chemical vapor deposition).
Graphene synthesis with chemical vapor deposition directly over Si wafer with surface oxide (Si/SiOx ) has proven challenging in terms of large area and uniform layer number. The direct growth of graphene over Si/SiO x substrate becomes attractive because it is free of an undesirable transfer procedure, necessity for synthesis over metal substrate, which causes breakage, contamination and time consumption. To obtain homogeneous graphene growth, a local equilibrium chemical environment has been established with a facile confinement CVD approach, inwhich two Si wafers with their oxide faces in contact to form uniform monolayer graphene. A thorough examination of the material reveals it comprises facetted grains despite initially nucleating as round islands. Upon clustering these grains facet to minimize their energy, which leads to faceting in polygonal forms because the system tends to ideally form hexagons (the lowest energy form). This is much like the hexagonal cells in a beehive honeycomb which require the minimum wax. This process also results in a near minimal total grain boundary length per unit area. This fact, along with the high quality of the resultant graphene is reflected in its electrical performance which is highly comparable with graphene formed over other substrates, including Cu. In addition the graphene growth is self-terminating, which enables the wide parameter window for easy control.
This chemical vapor deposition approach is easily scalable and will make graphene formation directly on Si wafers competitive against that from metal substrates which suffer from transfer. Moreover, this growth path shall be applicable for direct synthesis of other two dimensional materials and their Van der Waals hetero-structures.
in bus shelter, railway station and airport waiting hall due to its semi-transparency
with transparent conducting oxide as back electrode. Meanwhile, it is suitable in
tandem solar cells. However, the rectifying junction between transparent conducting
oxide and Cu(In,Ga)Se 2 absorbers deteriorates the cell performance. Thus, the contact
issue of ZnO:Ga and Cu(In,Ga)Se 2 were analyzed and solved in this thesis. Bifacial
CIGS solar cells were fabricated with ZnO:Ga/ MoSe 2 back electrode.
To begin with, the history of energy exploits and solar cells, the development
milestones of Cu(In,Ga)Se 2 solar cells are listed in the first chapter. Following is
detailed information of bifacial CIGS solar cells. And then, the device structure of
bifacial solar cells and the deposition process for each layer are simplified together
with the characterization methods.
Thereafter, the selenization parameters of Mo thin films both on bare soda lime
glass and on ZnO:Ga coated one were exploited and optimized, i.e. the substrate
temperature and the sodium incorporation. The addition of MoSe 2 into ZnO:Ga/
CIGS interface and its effect on the contact were studied.
Finally, CIGS solar cells were fabricated on both ZnO:Ga electrodes and
ZnO:Ga/ MoSe 2 back contact. Cell performances were carried on under the
illumination of AM 1.5 sun simulator. Quantum efficiencies were also measured with
crystal silicon solar cells as references. Further modification for solar cells are
delivered with comparison and analysis of parameters related to improving current
solar cells.
Key Words: transparent conducting oxide, bifacial solar cells, MoSe2, CIGS thin film, ZnO:Ga
Keywords: transition metal dichalcogenides; WSe2; optoelectronics; photodetectors; transistors; layered noble metal dichalcogenides
first stage, the substrate temperature is 350 o C, subsequently the substrate temperature is kept on 450 o C in second and third stages.
The configuration of CIGS thin film-based solar cell is as SLG/Mo/CIGS/CdS/ZnO/ZnO:Al/Ni-Al. grid, and the heterojunction is
formed between P type CIGS and N type CdS. In our work, the temperature-dependent current-voltage (JVT) measurements on
CIGS solar cells are investigated. The active energy is extracted from JVT measurement data. Simultaneously, the ideality factors in
different temperature are fitted by tunneling enhanced recombination models, which can deduce the characteristic tunneling energy
and characteristic energy of defect distribution. Finally, the dominated recombination mechanisms and paths is determined。 This
result is helpful to further understand the electrical transport of this device.
Key words: solar cells, CIGS thin film absorber, recombination paths