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Fang, S-L, Chou T-chin, Samireddi S, Chen K-H, Chen L-C, Chen W-F.  2017.  Enhanced hydrogen evolution reaction on hybrids of cobalt phosphide and molybdenum phosphide, 2017/03/01. Royal Society open science. 4(3):161016161016-161016.: The Royal Society Publishing AbstractWebsite

Production of hydrogen from water electrolysis has stimulated the search of sustainable electrocatalysts as possible alternatives. Recently, cobalt phosphide (CoP) and molybdenum phosphide (MoP) received great attention owing to their superior catalytic activity and stability towards the hydrogen evolution reaction (HER) which rivals platinum catalysts. In this study, we synthesize and study a series of catalysts based on hybrids of CoP and MoP with different Co/Mo ratio. The HER activity shows a volcano shape and reaches a maximum for Co/Mo = 1. Tafel analysis indicates a change in the dominating step of Volmer-Hyrovský mechanism. Interestingly, X-ray diffraction patterns confirmed a major ternary interstitial hexagonal CoMoP(2) crystal phase is formed which enhances the electrochemical activity.

Wei-ChaoChen, Cheng-YingChen, Tunuguntla V, HungLu S, ChaochinSu, Lee C-H, Chen K-H, Chen L-C.  2016.  Enhanced solar cell performance of Cu2ZnSn(S,Se)4 thin films through structural control by using multi-metallic stacked nanolayers and fast ramping process for sulfo-selenization. Nano Energy. 30:762-770.
Wong, DP, Huang CY, Chien WL, Chang CE, Ganguly A, Lyu LM, Hwang JS, Chen LC, Chen KH.  2016.  Enhanced thermoelectric performance in percolated bismuth sulfide composite. RSC Advances . 6:98952.
Valiyaveettil, SM, Nguyen D-L, Wong DP, Hsing C-R, Paradis-Fortin L, Qorbani M, Sabbah A, Chou T-L, Wu K-K, Rathinam V, Wei C-M, Chen L-C, Chen K-H.  2022.  Enhanced Thermoelectric Performance in Ternary Skutterudite Co(Ge0.5Te0.5)3 via Band Engineering, 2022. Inorganic Chemistry. : American Chemical Society AbstractWebsite

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Chang, H-C, You H-J, Sankar R, Yang Y-J, Chen L-C, Chen K-H.  2019.  Enhanced thermoelectric performance of BiCuTeO by excess Bi additions, 2019. 45(7, Part A):9254-9259. AbstractWebsite

Thermoelectric (TE) devices used to convert waste heat directly into electricity are highly desirable for alleviating the prevailing energy crisis and global climate-change issues. Among the various TE materials available, metal oxides exhibit high thermal and chemical stabilities in air, and are hence, preferred for use in many TE applications. However, most of them possess TE figures of merit (ZT) that are below the applicable value of 2, in the mid-temperature region (from 250 to 600 °C). In a previous work, the removal of a small amount of Bi from BiCuSeO was found to improve the ZT of BiCuSeO. In this work, we pursue another track and study the TE performance of BiCuTeO after the addition of up to 6% excess Bi. Bi1+xCuTeO (x = 0.00–0.06) samples were prepared by solid-state reactions, followed by hot-pressing to form pellets. By adding a stoichiometric excess of Bi into BiCuTeO, 16% enhancement in power factor was achieved at 450 °C. This enhancement can be attributed to the increase in the Seebeck coefficient because of the appearance of secondary phases. Detailed characterizations and discussions of the effect of the nominal excess Bi in BiCuTeO are presented in this paper. The findings of this study can be applied in the investigation of novel high-performance TE materials.

Bayikadi, KS, Sankar R, Wu CT, Xia C, Chen Y, Chen L-C, Chen K-H, Chou F-C.  2019.  Enhanced thermoelectric performance of GeTe through in situ microdomain and Ge-vacancy control, 2019. Journal of Materials Chemistry A. 7(25):15181-15189.: The Royal Society of Chemistry AbstractWebsite

A highly reproducible sample preparation method for pure GeTe in a rhombohedral structure without converting to the cubic structure up to ∼500 °C is reported to show control of the Ge-vacancy level and the corresponding herringbone-structured microdomains. The thermoelectric figure-of-merit (ZT) for GeTe powder could be raised from ∼0.8 to 1.37 at high temperature (HT) near ∼500 °C by tuning the Ge-vacancy level through the applied reversible in situ route, which made it highly controllable and reproducible. The enhanced ZT of GeTe was found to be strongly correlated with both its significantly increased Seebeck coefficient (∼161 μV K−1 at 500 °C) and reduced thermal conductivity (∼2.62 W m−1 K−1 at 500 °C) for a sample with nearly vacancy-free thicker herringbone-structured microdomains in the suppressed rhombohedral-to-cubic structure phase transformation. The microdomain and crystal structures were identified with HR-TEM (high-resolution transmission electron microscopy) and powder X-ray diffraction (XRD), while electron probe micro-analysis (EPMA) was used to confirm the stoichiometry changes of Ge : Te. Theoretical calculations for GeTe with various Ge-vacancy levels suggested that the Fermi level shifts toward the valence band as a function of increasing the Ge-vacancy level, which is consistent with the increased hole-type carrier concentration (n) and effective mass (m*) deduced from the Hall measurements. The uniquely prepared sample of a near-vacancy-free GeTe in a rhombohedral structure at high temperature favoured an enhanced Seebeck coefficient in view of the converging L- and Σ-bands of the heavy effective mass at the Fermi level, while the high density domain boundaries for the domain of low carrier density were shown to reduce the total thermal conductivity effectively.

Sankar, R, Wong DP, Chi CS, Chien WL, Hwang JS, Chou FC, Chen LC, Chen KH.  2015.  Enhanced thermoelectric performance of GeTe-rich germanium antimony tellurides through the control of composition and structure. CrystEngComm, . 17:3440.
Valiyaveettil, SM, Qorbani M, Hsing C-R, Chou T-L, Paradis-Fortin L, Sabbah A, Srivastava D, Nguyen D-L, Ho T-T, Billo T, Ganesan P, Wei C-M, Chen L-C, Chen K-H.  2022.  Enhanced thermoelectric performance of skutterudite Co1−yNiySn1.5Te1.5−x with switchable conduction behavior, 2022. Materials Today Physics. 28:100889. AbstractWebsite

A fine control of carriers in solids is the most essential thing while exploring any functionality. For a ternary skutterudite like CoSn1·5Te1.5−x, which has been recently recognized as a potential material for thermoelectric conversion, the dominant carrier could be either electrons or holes via chemically tuning the quaternary Sn2Te2 rings in the structure. Both theoretical calculation and different spectroscopic probes, such as X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) were employed to unveil the conduction type switching details. On the other hand, a Ni-for-Co substitution was applied to enhance electronic transport, and thereby the thermoelectric power factor. Thanks to the substantial cut-off of lattice thermal conductivity by the characteristic Sn2Te2 rings in the skutterudite structure, ultimately a 70-fold increase in the dimensionless figure-of-merit (zT) is achieved at 723 K with the nominal composition Co0·95Ni0·05Sn1·5Te1.5.

Chang, H-C, You H-J, Sankar R, Yang Y-J, Chen L-C, Chen K-H.  2019.  Enhanced Thermoelectric Performance via Oxygen Manipulation in BiCuTeO, 2019. MRS Advances. 4(8):499-505.: Materials Research Society AbstractWebsite

BiCuTeO is a potential thermoelectric material owing to its low thermal conductivity and high carrier concentration. However, the thermoelectric performance of BiCuTeO is still below average and has much scope for improvement. In this study, we manipulated the nominal oxygen content in BiCuTeO and synthesized BiCuTeOx (x = 0.94–1.06) bulks by a solid-state reaction and pelletized them by a cold-press method. The power factor was enhanced by varying the nominal oxygen deficiency due to the increased Seebeck coefficient. The thermal conductivity was also reduced due to the decrease in lattice thermal conductivity owing to the small grain size generated by the optimal nominal oxygen content. Consequently, the ZT value was enhanced by ∼11% at 523 K for stoichiometric BiCuTeO0.94 compared to BiCuTeO. Thus, optimal oxygen manipulation in BiCuTeO can enhance the thermoelectric performance. This study can be applied to developing oxides with high thermoelectric performances.

Kichambare, PD, Tarntair FG, Wang TY, Chen LC, Chen KH, Cheng HC.  1999.  Enhancement in Field Emission of Silicon Micro-tips by Bias-assisted Carburization. the Appl. Diamond Conference and Frontier Carbon Tech. Joint Conference 1999. :353-358., Tsukuba, Japan
Kichambare, PD, Tarntair FG, Wang TY, Chen LC, Chen KH, Cheng HC.  2000.  Enhancement in field emission of silicon microtips by bias-assisted carburization. J. Vac. Sci. Tech.. B18:2722-2729.
Ramakrishnan, A, Raman S, Chen L-C, Chen K-H.  2017.  Enhancement in Thermoelectric Properties of TiS2 by Sn Addition. Journal of Electronic Materials. :1–8.
Tunuguntla, V, Chen WC, Newman TD, Hsieh MC, Lu SH, Su C, Chen LC, Chen KH.  2016.  Enhancement of charge collection at shorter wave lengths from alternative CdS deposition conditions for high efficiency CZTSSe solar cells. Solar Energy Materials & Solar Cells . 149:49-54.
Ray, SC, Palnitkar U, Pao CW, Tsai HM, Pong* WF, Lin I-N, Papakonstantinou P, Chen LC, Chen KH.  2009.  Enhancement of electron field emission of nitrogenated carbon nanotubes on chlorination. Diamond Relat. Mater.. 18:457-460.
Han, HC, Tseng CA, Du CY, A.Ganguly, Chong CW, Wang SB, Lin CF, Chang SH, Su CC, Lee JH, Chen KH, Chen LC.  2012.  Enhancing efficiency with fluorinated interlayer in small molecule organic solar cell. J. Mater. Chem.. 22:22899.
Venugopal, B, Syum Z, Yu S-Y, Sabbah A, Shown I, Chu C-W, Chen L-C, Lee C-H, Wu H-L, Chen K-H.  2022.  Enhancing the Areal Capacity and Stability of Cu2ZnSnS4 Anode Materials by Carbon Coating: Mechanistic and Structural Studies During Lithiation and Delithiation, 2022. ACS Omega. 7(11):9152-9163.: American Chemical Society AbstractWebsite

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Syum, Z, Billo T, Sabbah A, kumar Anbalagan A, Quadir S, Hailemariam AG, Sabhapathy P, Lee C-H, Wu H-L, Chen L-C, Chen K-H.  2023.  Enhancing the lithium-ion storage capability of Cu2ZnSnS4 anodes via a nitrogen-doped conductive support, 2023. Chemical Engineering Journal. 465:142786. AbstractWebsite

Achieving lithium-ion batteries with both excellent electrochemical performance and cycling stability is a top priority for their real-world applications. This work reports high-performance and stable Cu2ZnSnS4 (CZTS) anode materials encapsulated by nitrogen-doped carbon (CZTS@N-C) for advanced lithium-ion battery application. Ex-situ X-ray photoelectron spectroscopy and transmission electron microscopy revealed that the nitrogen-doped carbon network features a more conducive solid-electrolyte interphase that enables lower charge-transfer resistance and fast Li+ diffusion kinetics with negligible initial irreversible capacity loss. As a result, the CZTS@N-C electrode delivers a significantly enhanced capacity of 710 mAh g−1 with 73% capacity retention after 220 cycles at a current rate of 0.5 mA g−1 and superior rate performance compared to that of unmodified CZTS. Additionally, the study sheds light on the fast lithiation dynamics chemistry of CZTS@N-C through kinetics analysis, explored by in-situ Raman, ex-situ X-ray absorption, and in-situ electrochemical impedance. This study provides a new approach for fabricating high-performance, durable conductive polymer-encapsulated low-cost transition-metal-sulfide anode materials.

Ho, T-T, Jokar E, Quadir S, Chen R-S, Liu F-C, Cheng-YingChen, Chen K-H, Chen L-C.  2022.  Enhancing the photovoltaic properties of SnS-Based solar cells by crystallographic orientation engineering, 2022. Solar Energy Materials and Solar Cells. 236:111499. AbstractWebsite

Tin monosulfide (SnS) is a promising light-harvesting material for solar cell applications, owing to its potential for large-scale production, cost-effectiveness, eco-friendly source materials, and long-term stability. However, SnS crystallizes in an orthorhombic structure, which results in a highly anisotropic charge transport behavior. Tailoring the crystallographic orientation of the SnS absorber layer plays a critical role in the enhancement of the transfer of charge carriers and the power conversion efficiency (PCE). By controlling the substrate tilting angle and temperature ramp rate in vapor transport deposition, the crystal growth orientation was tuned to a preferred direction which significantly suppressed the unfavorable (040) crystallographic plane. Through the combination of these two approaches, the PCE could be increased from 0.11% to 2%. The effect of the tilting angle was numerically simulated to investigate its role in controlling the film uniformity and directing the film growth. In addition, the correlation between the texture coefficient of the (040) plane and the charge transport properties was determined by a combination of analytical methods such as device performance studies, electrochemical impedance spectroscopy, along with transient photovoltage, space-charge-limited current, and dark current measurements. These techniques were blended together to prove that the marked improvement in PCE can be ascribed to a reduced charge recombination (in both SnS bulk and interfaces) and an enhanced hole mobility.

Chen, KH, Wu JY, Chen LC, Juan CC, Hsu T.  1995.  Epitaxial Growth of Diamond Films for Electronic Applications. the 188th Meeting of the Electrochemical Society. :Vol95-21,p55-69., Chicago
Chen, JT, Hsiao CL, Hsu HC, Wu CT, Yeh CL, Wei PC, Chen LC, Chen* KH.  2007.  Epitaxial growth of InN films by molecular-beam epitaxy using hydrazoic acid (HN3) as an efficient nitrogen source. J. Phys. Chem. A. 111:6755-6759.