Kuei-Hsien Chen

Abstract The present investigation mainly addresses the open circuit voltage (Voc) issue in kesterites based Cu2ZnSn(S,Se)4 solar cells by simply introducing alkali metal fluoride nanolayers (  several nm NaF, or LiF) to lower the work functions of the front İTO\} contacts without conventional hole-blocking ZnO layers. Kelvin probe measurements confirmed that the work function of the front İTO\} decreases from 4.82 to 3.39 and 3.65 eV for NaF and LiF, respectively, resulting in beneficial band alignment for electron collection and/or hole blocking on top electrodes. Moreover, a 10.4% power conversion efficiency ( 11.5% in the cell effective area) \{CZTSSe\} cell with improved Voc of up to 90 mV has been attained. This demonstration may provide a new direction of further boosting the performance of copper chalcogenide based solar cells as well.

The present investigation mainly addresses the open circuit voltage (Voc) issue in kesterite based Cu2ZnSn(S,Se)4 solar cells by simply introducing alkali metal fluoride nanolayers (~ several nm NaF, or LiF) to lower the work functions of the front ITO contacts without conventional hole-blocking ZnO layers. Kelvin probe measurements confirmed that the work function of the front ITO decreases from 4.82 to 3.39 and 3.65 eV for NaF and LiF, respectively, resulting in beneficial band alignment for electron collection and/or hole blocking on top electrodes. Moreover, a 10.4% power conversion efficiency (~ 11.5% in the cell effective area) CZTSSe cell with improved Voc of up to 90 mV has been attained. This demonstration may provide a new direction of further boosting the performance of copper chalcogenide based solar cells as well.

As a lead-free high-performance thermoelectric material, germanium telluride (GeTe) has recently been extensively studied for mid-temperature (500–800 K) applications. The carrier concentration and the thermal conductivity are reduced for vacancy-controlled GeTe compounds compared with pristine GeTe. We explored and optimized the Ge0.9−xSb0.1PxTe (x = 0.01–0.05) material's highest thermoelectric performance at elevated temperatures. Intrinsic Ge vacancy control and manipulation of Ge (+2) with Sb/P (+3) increased the charge contribution to power factor improvement to ∼42 µWcm−1 K−2 while minimizing the lattice thermal contribution to ∼0.4 W/mK. This resulted in an increase in thermoelectric performance of ∼2.4 @ 773 K for the Ge0.88Sb0.1P0.02Te sample. The inclusion of atomically disordered Sb/P ions considerably increases the scattering effects caused by the point defect, whereas stretched grain boundaries reveal the decreased lattice thermal contribution. The current work demonstrates the effectiveness of phosphorus as a co-dopant in increasing the average thermoelectric performance (ZTavg) value over the GeTe operating temperature range.

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.

Gas-phase photocatalytic reactions to convert carbon dioxide and water into oxygen and hydrocarbons are the foundation of life on earth. However, the efficiency of photosynthesis is relatively low (~1%), which leaves much room for artificial photosynthesis to reach the benchmark of the solar cells (>15%). In this work, carbon implanted SnS2 thin films (C–SnS2) were prepared to study photocatalytic activity and adsorbate-catalyst surface interactions during CO2 photoreduction. The electron density distribution in C–SnS2 and its contribution toward the photogenerated charge transfer process has been analyzed by the angle-dependent X-ray absorption near-edge structure (XANES) study. The C–SnS2 surface affinity toward the CO2 molecule was monitored by in-situ dark current and Raman spectroscopy measurements. By optimizing the dose during ion implantation, SnS2 thin film with 1 wt% carbon incorporation shows 108 times enhancement in the CO2 conversion efficiency and more than 89% product selectivity toward CH4 formation compared with the as-grown SnS2 without carbon incorporation. The improved photocatalytic activity can be ascribed to enhanced light harvesting, pronounced charge-transfer between SnS2 and carbon with improved carrier separation and the availability of highly active carbon sites that serve as favorable CO2 adsorption sites.

Abstract Sulfonated polyaryletherketones (SPAEK) bearing four sulfonic acid groups on the phenyl side groups were synthesized. The benzophenone moiety of polymer backbone was further reduced to benzydrol group with sodium borohydride. The membranes were crosslinked by acid-catalyzed Friedel-Crafts reaction without sacrifice of sulfonic acid groups and ion exchange capacity (IEC) values. Crosslinked membranes with the same IEC value but different water uptake could be prepared. The optimal crosslinking condition was investigated to achieve lower water uptake, better chemical stability (Fenton's test), and higher proton conductivity. In addition, the hydrophilic ionic channels from originally course and disordered could be modified to be narrow and continuous by this crosslinking method. The crosslinked membranes, CS4PH-40-PEKOH (IEC = 2.4 meq./g), reduced water uptake from 200 to 88% and the weight loss was reduced from 11 to 5% during the Fenton test compared to uncrosslinked one (S4PH-40-PEK). The membrane showed comparable proton conductivity (0.01?0.19?S/cm) to Nafion 212 at 80°C from low to high relative humidity (RH). Single H2/O2 fuel cell based on the crosslinked SPAEK with catalyst loading of 0.25?mg/cm2 (Pd/C) exhibited a peak power density of 220.3 mW/cm2, which was close to that of Nafion 212 (214.0 mW/cm2) at 80°C under 53% RH. These membranes provide a good option as proton exchange membrane with high ion exchange capacity for fuel cells.

Designing an organic polymer photocatalyst for efficient hydrogen evolution with visible and near-infrared (NIR) light activity is still a major challenge. Unlike the common behavior of gradually increasing the charge recombination while shrinking the bandgap, we present here a series of polymer nanoparticles (Pdots) based on ITIC and BTIC units with different π-linkers between the acceptor-donor-acceptor (A-D-A) repeated moieties of the polymer. These polymers act as an efficient single polymer photocatalyst for H2 evolution under both visible and NIR light, without combining or hybridizing with other materials. Importantly, the difluorothiophene (ThF) π-linker facilitates the charge transfer between acceptors of different repeated moieties (A-D-A-(π-Linker)-A-D-A), leading to the enhancement of charge separation between D and A. As a result, the PITIC-ThF Pdots exhibit superior hydrogen evolution rates of 279 µmol/h and 20.5 µmol/h with visible (>420 nm) and NIR (>780 nm) light irradiation, respectively. Furthermore, PITIC-ThF Pdots exhibit a promising apparent quantum yield (AQY) at 700 nm (4.76%).