Jinbo Pang | University Of Jinan (original) (raw)

Papers by Jinbo Pang

Applied Surface Science, 2024

Germanous selenide (GeSe) is an emerging photoactive layer material due to its excellent photoele... more Germanous selenide (GeSe) is an emerging photoactive layer material due to its excellent photoelectric properties, low cost and environmental friendliness. However, severe carrier recombination in the GeSe photoactive layer remains a significant factor limiting the conversion efficiency of GeSe solar cells. In this study, the GeSe photoactive layers were doped copper chloride (CuCl 2) solution, enabling the distribution of Cu 2+ ions throughout the layer, primarily accumulating on the GeSe grain surface. Its impact on the carrier transport in the GeSe photoactive layer was studied by ultraviolet photoelectron spectroscopy, kelvin probe force microscopy, and transient photovoltage. The doping can not only increase the Fermi level of the GeSe, but also adjust the local built-in potential on grain boundaries, so that the charge carriers can be redistributed in the three-dimensional space. Notably, at the grain boundaries, the hole flow before doping changes to electron flow, effectively reduces the recombination probability of charge carriers, and increases the carrier lifetime from 200.23 to 374.57 μs. As a result, the conversion efficiency after processing with CuCl 2 is increased from 1.98 % to 3.01 %. This study provides a reference for understanding the carrier kinetics in GeSe solar cells to improve the photoelectric conversion performance of the device.

Advanced Functional Materials, 2024

Recently, field-effect transistors (FETs) have emerged as a novel type of multiparameter, high-pe... more Recently, field-effect transistors (FETs) have emerged as a novel type of multiparameter, high-performance, highly integrated platform for biochemical detection, leveraging their classical three-terminal structure, working principles, and fabrication methods. Notably, graphene materials, known for their exceptional electrical and optical properties as well as biocompatibility, serve as a fundamental component of these devices, further enhancing their advantages in biological detection. This review places special emphasis on recent advancements in graphene field-effect transistor (GFET)-based biosensors and focuses on four main areas: i) the basic concepts of FETs and the specific electrical properties of GFETs; ii) various state-of-the-art approaches to enhance the performance of GFET-based biosensors in terms of operating principles and the "3S"-stability, sensitivity, and specificity; iii) multiplexed detection strategies for GFET-based biosensors; and iv) the current challenges and future perspectives in the field of GFET-based biosensors. It is hoped that this article can profoundly elucidate the development of GFET biosensors and inspire a broader audience.

Advanced Functional Materials, 2024

Pathogenic bacteria are commonly found in food, water, and soil, posing significant public health... more Pathogenic bacteria are commonly found in food, water, and soil, posing significant public health challenges globally. Therefore, early, rapid, and highly sensitive strategies for monitoring the bacterial proliferation are crucial for ensuring public health, medical diagnosis, and food safety. Compared to traditional techniques, microfluidic platforms provide powerful detective tools characterized by high integration, high throughput, ease of operation, low reagent consumption, and high sensitivity. Driven by substantial commercial demand, research and development in microfluidic-based rapid detection methods and technologies has progressed significantly derived by the interdisciplinary integration of multiple disciplines. In this review, progress in clinical detection of pathogenic bacteria with microfluidic biosensors, including microfluidic devices for point-of-care (POC) testing, is summarized. Strategies for pathogenic bacteria detection, containing their advantages and disadvantages are discussed in detail. Advanced platforms for capturing and detecting pathogenic bacteria, such as microchannels, microarrays, digital microfluidics (DMF) and paper-based platforms, are highlighted. The accomplishments and shortcomings of these microfluidic devices are also summarized. Additionally, case studies of biosensor-based microfluidic devices used for detecting diseases caused by bacterial imbalances are listed. Finally, possible research perspectives for further development in highly effective biosensor-based microfluidics for clinical detection of pathogenic bacteria are proposed.

Soft science, May 14, 2024

The skin, a vital medium for human-environment communication, stands as an indispensable and pivo... more The skin, a vital medium for human-environment communication, stands as an indispensable and pivotal element in the realms of both production and daily life. As the landscape of science and technology undergoes gradual evolution and the demand for seamless human-machine interfaces continues to surge, an escalating need emerges for a counterpart to our biological skin-electronic skins (e-skins). Achieving high-performance sensing capabilities comparable to our skin has consistently posed a formidable challenge. In this article, we systematically outline fundamental strategies enabling e-skins with capabilities including strain sensing, pressure sensing, shear sensing, temperature sensing, humidity sensing, and self-healing. Subsequently, complex e-skin systems and current major applications were briefly introduced. We conclude by envisioning the future trajectory, anticipating continued advancements and transformative innovations shaping the dynamic landscape of e-skin technology. This article provides a profound insight into the current state of e-skins, potentially inspiring scholars to explore new possibilities.

Social Science Research Network, 2022

Optical Materials, Feb 1, 2020

A 2.5 nm-thickness tungsten disulfide (WS 2) saturable absorber (SA) was successfully fabricated ... more A 2.5 nm-thickness tungsten disulfide (WS 2) saturable absorber (SA) was successfully fabricated by the electron beam evaporation (EBE) combined with post vulcanization. By applying the prepared WS 2 SA to an acousto-optic (AO) Q-switched fundamental laser, a dual-loss-modulated Q-switched intracavity optical parametric oscillator (IOPO) has been experimentally realized. Because of the participation of WS 2 SA, the problem of output decline was alleviated when the pump power was between 8.6 W and 10.8 W. The pulse width could be maximally compressed by 73% in WS 2 SA based active-passive Q-switched IOPO with 10 kHz pulse-repetition rate, and the shortest pulse width in experiment was 1.098 ns. Benefiting from the pulse compression, the maximum pulse peak power in dual-loss-modulated Q-switched IOPO was 427% higher than that in AO active Q-switched IOPO. The application of WS 2 SA also contributed to the stability of signal pulse train whose root mean square error (RMS) was efficiently lowered from 0.01776 to 0.00954. The nonlinear conversion efficiency was improved by approximate 38.2% in the dual-loss-modulated Q-switched IOPO.

Applied Physics Express, Apr 16, 2020

A dual-loss Q-switched laser was realized by applying a home-made 2.5 nm thick WTe2 to an acousto... more A dual-loss Q-switched laser was realized by applying a home-made 2.5 nm thick WTe2 to an acousto-optic modulated laser. Besides conventional pulse compression, the inclusion of WTe2 could obviously improve the average output power by 29.6% and reduce the laser threshold by 20%, even with the introduced 8% nonsaturable loss. The average output-power improvement and pulse compression in this dual-loss modulated laser resulted in a 113.7% increase of peak power. According to the measured spectra of the laser and the photoluminescence of WTe2, the laser-induced excitonic light emission may be the reason for this laser's gain.

Optics Express, Nov 27, 2019

A 2.5nm-thickness molybdenum diselenide (MoSe2) saturable absorber (SA) is prepared by electron b... more A 2.5nm-thickness molybdenum diselenide (MoSe2) saturable absorber (SA) is prepared by electron beam evaporation (EBE) method. Applying the prepared MoSe2 SA to an acousto-optic (AO) Q-switched fundamental laser, a dual-loss-modulated intra-cavity optical parametric oscillator (IOPO) has been experimentally realized. The signal-pulse train from this IOPO has 0.0053 standard deviation (SD) of pulse amplitude. When the MoSe2 SA is applied to IOPO, the signal pulse is compressed by maximum 68%, the peak power increases by 274%, and the nonlinear conversion increases by 12.6%. To solve the established rate equation of IOPO, the ground-state and excited-state absorption cross section of MoSe2 are rationally estimated to be 1.04×10-18cm-2 and 6.25×10-19cm-2 from the measured transmittance curve, and the excited-state lifetime is 275.6µs. The numerical solution of the equations fits the experimental data well.

ACS applied energy materials, Mar 11, 2020

In this work, the molybdenum oxide (MoOx) was employed as a back contact layer to improve the dev... more In this work, the molybdenum oxide (MoOx) was employed as a back contact layer to improve the device performance of ultrathin Cu(In,Ga)Se2 (CIGS) solar cells with CIGS absorber synthesized through the low-temperature three-stage co-evaporation process. This contribution focuses on the investigation of the inherent mechanisms and the improved device performance in detail. Our research shows that the energy band of the CIGS/Mo interface can be tuned and the Schottky barrier can be reduced. Compared with the reference sample without MoOx, the back barrier height of the new device with 10 nm MoOx enjoys a significant decrease from 43.83 to 15.98 meV because of the improvement of energy band structure. Meanwhile, the results of wxAMPS simulation corroborate that the energy band bends upward in the devices with an appropriate thickness of MoOx films, which facilitates the carrier transportation and suppresses the recombination of charge carriers at the MoOx/Cu(In,Ga)Se2 interface. Moreover, the carriers can transport through the MoOx/CIGS interface by tunneling when the MoOx film is thin enough. Finally, by controlling the thicknesses of MoOx films, an efficiency of 10.38% is achieved in 0.5 μm CIGS solar cells by optimizing the MoOx thickness under the low-temperature three-stage co-evaporation process.

Small methods, May 11, 2020

Contact engineering, especially at the interface between metal and 2D semiconductors, to enable h... more Contact engineering, especially at the interface between metal and 2D semiconductors, to enable high‐performance devices remains a formidable challenge due to the inevitable chemical disorder and Fermi‐level pinning at the interface. Here, the authors report the InSe–Se vertical van der Waals (vdW) heterostructures to achieve high field‐effect mobility and electrical stability in 30 nm InSe field‐effect transistor (FET), which has a low lattice mismatch of 1.1% and form 2D/2D low‐resistance contacts, creating an InSe contact interface that substantially limits chemical disorder and Fermi‐level pinning. The Se layer forms a vdW contact to prevent the damage induced by direct metallization and acts as a tunneling layer as well as a protective encapsulation layer. Using this approach, heterojunction devices with a high field‐effect mobility of ≈2500 cm2 (V s)−1 and an excellent on‐state current of ≈10−3 A at room temperature is achieved. Furthermore, the device field‐effect mobility degrades by only 3.46% following two months of storage time in open air, which represents the best electrical stability reported to date. In particular, the heterojunction devices exhibit a better photoresponsivity compared with InSe devices in practical application. This study provides a highly valuable strategy to improve the contact condition of metal/2D semiconductors for high‐performance, 2D‐based electronics and optoelectronics.

Journal of Materials Science, Oct 3, 2019

Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for sensing, which can detect a bro... more Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for sensing, which can detect a broad range of chemical and biological analytes at the singlemolecule level. In this work, a hybrid structure of Au nanodot array and highquality graphene monolayer is used as SERS substrate, which integrates the electromagnetic enhancement from Au nanodots and chemical enhancement from monolayer graphene. The fabricated SERS substrates consist of uniform round top shape Au nanodot array with coverage of 36.9% where their diameter and gap distribution ranges from * 33 to * 42 nm and from * 22 to * 28 nm. The hybrid Au nanodot array/monolayer Gr SERS substrate exhibited a 4.67 times enhanced Raman signal compared to Au nanodots without Gr at the R6G concentration of 10-6 M. The detection limit of R6G is achieved as low as 4.69 9 10-9 M on the Au nanodot array/Gr SERS substrate. These experiments demonstrate a facile approach to fabricate hybrid metal nanostructure/2D materials SERS substrate for biomedical and environmental sensing and provide a clue for high-performance optoelectronic devices.

ACS applied electronic materials, Jun 16, 2020

Electrical stability and field-effect mobility of two-dimensional (2D) materials based fieldeffec... more Electrical stability and field-effect mobility of two-dimensional (2D) materials based fieldeffect transistors (FETs) are extremely important for practical electronic applications. Interface scattering during the transmission of 2D materials, which can be significantly influenced by the interface between dielectric and 2D materials, remain formidable challenges. Early work has achieved excellent mobility and on/off ratio, but the understanding and improvement of the electrical stability of MoS 2 devices is still in its infancy. Herein, a facile and effective strategy is proposed via spin-coated polymethyl methacrylate (PMMA) dual layer to enhance both fieldeffect mobility and electrical stability of molybdenum disulfide (MoS 2) FETs, in which the PMMA underneath MoS 2 works as gate dielctric together with SiO 2 , and the PMMA on top of MoS 2 is used to protect FET channel from exposure to air. The field-effect electron mobility has been improved up to 2.5 times, from 41.8 to 104.6 cm 2 /Vs, by using PMMA/SiO 2 as back gate dielectric and PMMA capsulation layer. The time-and stress-dependent electrical stability has been essentially improved. Negligible threshold voltage shift (ΔV th <0.1V) and field-effect mobility degradation (1.4%) are achieved, upon a gate-bias voltage of ±35 V applying for 300 s, even after 45 days storage in open air. The effective suppression of interface impurities located at channel interface contributes to the electrical performance enhancement of MoS 2 FETs. Furthermore, a theoretical model was developed to investigate different MoS 2 /dielectric interface structures by density-functional theory (DFT) which is consistent with interface scattering theory. This study not only provides a clue for the high performance 2D FETs fabrication but also offers an opportunity to understand electrical properties degradation mechanism of the 2D materials family devices and push forward their practical applications in the 2D devices and flexible electronics.

ACS Applied Materials & Interfaces, Apr 9, 2019

Graphene, with its excellent chemical stability, biocompatibility, and capability of electric fie... more Graphene, with its excellent chemical stability, biocompatibility, and capability of electric field enhancement, has a great potential in optical and optoelectronic applications with superior performances by integrating with conventional optical and plasmonic devices. Here, we design and demonstrate graphene-activated optoplasmonic cavities based on rolled-up nanomembranes, which are employed for in situ monitoring the photodegradation dynamics of organic dye molecules on the molecular level in real time. The presence of the graphene layer significantly enhances the electric field of hybrid optoplasmonic modes at the cavity surface, enabling a highly sensitive surface detection. The degradation of rhodamine 6G molecules on the graphene-activated sensor surface is triggered by localized laser irradiation and monitored by measuring the optical resonance shift. Our demonstration paves the way for real-time, high-precision analysis of photodegradation by resonance-based optical sensors, which promises the comprehensive understanding of degradation mechanism and exploration of effective photocatalysts.

Solar RRL, Feb 26, 2021

Antimony chalcogenides have become a family of promising photoelectric materials for high‐efficie... more Antimony chalcogenides have become a family of promising photoelectric materials for high‐efficiency solar cells. To date, single‐junction solar cells based on individual antimony selenide or sulfide are dominant and show limited photoelectric conversion efficiency. Therefore, great gaps remain for the multiple junction solar cells. Herein, triple‐junction antimony chalcogenides‐based solar cells are designed and optimized with a theoretical efficiency of 32.98% through band engineering strategies with Sb2S3/Sb2(S0.7Se0.3)3/Sb2Se3 stacking. The optimum Se content of the mid‐cell should be maintained low, i.e., 30% for achieving a low defect density in an absorber layer. Therefore, Sb2(S0.7Se0.3)3‐based mid solar cells have contributed to elevate the external quantum efficiency in triple‐junction devices by the full utilization of the solar spectrum. In a single‐junction solar cell, the bandgap gradient is regulated through the Se content gradient along the depth profile of Sb2(S1−xSex)3. Besides, an increasing Se content profile provides an additional built‐in electric field for boosting hole charge carrier collection. Thus, the high charge carrier generation rate leads to a 17.96% improvement in the conversion efficiency compared with a conventional cell. This work may pave the way to boost the conversion efficiency of antimony chalcogenides‐based solar cells to their theoretical limits.

Advanced Optical Materials, Dec 18, 2017

Patterned plasmonic nanodimers are fabricated exploiting an ultrathin porous anodic aluminum oxid... more Patterned plasmonic nanodimers are fabricated exploiting an ultrathin porous anodic aluminum oxide membrane as a mask during angle‐resolved shadow deposition. The fabricated nanodimer arrays exhibit consistent sub‐10 nm gaps and a high particle density up to 1.0 × 1010 cm−2 over a large area. The ultrasmall dimer gaps provide highly confined electromagnetic fields, which strongly enhance the photoluminescence (PL) emission and Raman scattering from the surrounding monolayer molybdenum disulphide (MoS2). The ensemble PL intensity from MoS2/dimers is enhanced by up to a factor of ≈160 by resonant excitation of the dimer modes. Anisotropic polarization‐dependent characteristics of PL and Raman from the MoS2/dimers confirm that the dominant enhancement originates from the dimer configuration. These experiments demonstrate a facile approach for the fabrication of low‐cost high‐performance 2D material‐based optoelectronic devices.

Solar Energy Materials and Solar Cells, Mar 1, 2020

Sb 2 S 3 thin-film solar cells have recently gained attention due to their low cost, low toxicity... more Sb 2 S 3 thin-film solar cells have recently gained attention due to their low cost, low toxicity, and simple fabrication. However, there is still plenty of room to improve their performance. It is known that efficient carrier transport is essential for high performance Sb 2 S 3 solar cells, which, unfortunately, is difficult to characterize by conventional testing methods. Therefore, the carrier transport process in Sb 2 S 3 solar cells was studied here using a theoretical simulation. The results show that high solar performances can be achieved with a wide parameter window for selecting the electron transport layer as well as the hole transport layer, viz., with a conduction band minimum of the electron transport layer (À 4.4 eV < CBM < À 3.2 eV), and a valence band maximum of the hole transport layer (À 5.2 eV > VBM > À 6.4 eV). Here the interfacial potential barrier become negligible and as a consequence electrons and holes cross at ease, which guarantee the good device performance. Indeed, a Sb 2 S 3 solar cell with a high power conversion efficiency (PCE) can be obtained by ensuring that the carrier transport and collection are unimpeded in the device, i.e., the Sb 2 S 3-based single junction solar cells shows high efficiency of 19.53%. Furthermore, we found that optimized Sb 2 S 3 solar cells are particularly suitable for use as the top cell of tandem structure solar cells. Thus, a Sb 2 S 3 /Sb 2 Se 3 double junction solar cell structure was proposed. With a 0.5 μm thick Sb 2 S 3 absorber, double junction solar cells could achieve a theoretical efficiency as high as 26.64%. Our results based on the rotational design of bandgap alignment provide a general guide rule for selecting the optimal electron transport layer as well as the hole transport layer to boost the power conversion efficiency for Sb 2 S 3 solar cells up to its theoretical limit.

InfoMat, Mar 2, 2020

The pioneering exfoliation of monolayer tungsten diselenide has greatly inspired researchers towa... more The pioneering exfoliation of monolayer tungsten diselenide has greatly inspired researchers toward semiconducting applications. WSe2 belongs to a family of transition-metal dichalcogenides. Similar to graphene, WSe2 and analogous dichalcogenides have layered structures with weak van der Waals interactions between two adjacent layers. First, the readers are presented with the fundamentals of WSe2, such as types, morphologies, and properties. Here, we report the characterization principles and practices such as microscopy, spectroscopy, and diffraction. Second, the methods for obtaining high-quality WSe2, such as exfoliation, hydrothermal and chemical vapor deposition, are briefly listed. With advantages of light weight, flexibility, and high quantum efficiency, 2D materials may have a niche in optoelectronics as building blocks in p-n junctions. Therefore, we introduce a state-of-the-art demonstration of heterostructure devices employing the p-type WSe2 semiconductor. The device architectures include field-effect transistors, photodetectors, gas sensors, and photovoltaic solar cells. Due to its unique electronic, optical, and energy band properties, WSe2 has been increasingly investigated due to the conductivity of the p-type charge carrier upon palladium contact. Eventually, the dynamic research on WSe2 and van der Waals heterostructures is summarized to arouse the passion of the 2D research community.

Nano Energy, Aug 1, 2019

Molybdenum disulphide (MoS 2) presents a promising electrocatalyst for hydrogen evolution reactio... more Molybdenum disulphide (MoS 2) presents a promising electrocatalyst for hydrogen evolution reaction. Immense effort has been made to optimize MoS 2 catalysts with more active sites for the sake of satisfying HER performance. In this work, the MoS 2

Solar Energy Materials and Solar Cells, Sep 1, 2019

Sb 2 Se 3 as a rising star semiconducting material with a bandgap of 1.1 eV has played a role of ... more Sb 2 Se 3 as a rising star semiconducting material with a bandgap of 1.1 eV has played a role of the absorber in the thin film solar cells. Regular device architectures such as metal grids/buffer/Sb 2 Se 3 /metal electrode, or transparent electrode film/buffer/Sb 2 Se 3 /metal electrode have been fabricated both experimentally and theoretically and exhibit relatively good photovoltaic performances. Yet the theoretical power-conversion efficiency is not competitive with commercial thin film solar cells. Therefore, we propose an inverted architecture with top illumination through ITO substrate, with allocating the hole transport layer (HTL) on top of Sb 2 Se 3 and stacking electron transport layer beneath the Sb 2 Se 3. Indeed an optimal power conversion efficiency of 24.7% and fill factor of 80.3% have been simulated in the solar devices with the selected NiO as the HTL. The improvement in solar cell performances stems from the satisfying bandgap alignment and improved hole conductivity due to the high acceptor concentration of the chosen material. Further increase of the device performances depend on the high quality Sb 2 Se 3 thin films, i.e., with negligible defects states and the suppression of defects at the Sb 2 Se 3 / HTL interfaces.

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

Applied Surface Science, 2024

Advanced Functional Materials, 2024

Soft science, May 14, 2024

Social Science Research Network, 2022

Optical Materials, Feb 1, 2020

Applied Physics Express, Apr 16, 2020

Optics Express, Nov 27, 2019

ACS applied energy materials, Mar 11, 2020

Small methods, May 11, 2020

Journal of Materials Science, Oct 3, 2019

ACS applied electronic materials, Jun 16, 2020

ACS Applied Materials & Interfaces, Apr 9, 2019

Solar RRL, Feb 26, 2021

Advanced Optical Materials, Dec 18, 2017

Solar Energy Materials and Solar Cells, Mar 1, 2020

InfoMat, Mar 2, 2020

Nano Energy, Aug 1, 2019

Solar Energy Materials and Solar Cells, Sep 1, 2019

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

ACS Fall 2022, 2022

Keywords: transition metal dichalcogenides; WSe2; optoelectronics; photodetectors; transistors; layered noble metal dichalcogenides

ACS Spring Meeting 2021, 2021

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.