Shulin Ji

Thermal Response of Transparent Silver Nanowire/PEDOT:PSS Film Heaters

Thermal response behavior of transparent silver nanowire/PEDOT:PSS film heaters are intensively studied for manipulating heating temperature, response time, and power consumption. Influences of substrate heat capacity, heat transfer coefficient between air and heater, sheet resistance and dimension of Ag nanowire film, on the thermal response are investigated from thermodynamic analysis. Suggestion is given for practical applications that if other parameters are fixed, Ag nanowire coverage can be utilized as an effective parameter to adjust the thermal response. The heat transfer coefficient plays opposite roles on thermal response speed and achievable steady temperature. A value of ≈32 W m(-2) K(-1) is obtained from transient process analysis after correcting it by considering heater resistance variation during heating tests. Guidance of designing heaters with a given response time is provided by forming Ag nanowire film with a suitable sheet resistance on substrate of appropriate material and a certain thickness. Thermal response tests of designed Ag heaters are performed to show higher heating temperature, shorter response time, and lower power consumption (179 °C cm(2) W(-1)) than ITO/FTO heaters, as well as homogeneous temperature distribution and stability for repeated use. Potential applications of the Ag heaters in window defogging, sensing and thermochromism are manifested.

Photocurrent Enhancement for Ti-Doped Fe2O3 Thin Film Photoanodes by an In Situ Solid-State Reaction Method

In this work, a higher concentration of Ti ions are incorporated into hydrothermally grown Ti-doped (2.2% by atomic ratio) micro-nanostructured hematite films by an in situ solid-state reaction method. The doping concentration is improved from 2.2% to 19.7% after the in situ solid-state reaction. X-ray absorption analysis indicates the substitution of Fe ions by Ti ions, without the generation of Fe²⁺ defects. Photoelectrochemical impedance spectroscopy reveals the dramatic improvement of the electrical conductivity of the hematite film after the in situ solid-state reaction. As a consequence, the photocurrent density increases 8-fold (from 0.15 mA/cm² to 1.2 mA/cm²), and it further increases up to ∼1.5 mA/cm² with the adsorption of Co ions. Our findings demonstrate that the in situ solid-state reaction is an effective method to increase the doping level of Ti ions in hematite films with the retention of the micro-nanostructure of the films and enhance the photocurrent.

Micro-Nano-Structured Fe2O3:Ti/ZnFe2O4 Heterojunction Films for Water Oxidation

Iron(III) oxide photoelectrodes show promise in water oxidation applications. In this study, micro-nano-structured hematite films are synthesized, and Ti ions are doped to improve photoelectric conversion efficiency. The photocurrent increases for enhanced electrical conductivity. Further enhanced photocurrent is achieved for Fe(2)O(3):Ti/ZnFe(2)O(4) heterojunction electrodes. Cyclic voltammograms combined with optical absorbance examinations demonstrate that the conduction and valence band edges of ZnFe(2)O(4) shift from those of Ti doped Fe(2)O(3) to the negative direction, which facilitates the efficient separation of electron-hole pairs at the Fe(2)O(3):Ti/ZnFe(2)O(4) interface. These findings demonstrate that, by doping hematite and by engineering the interface between the hematite and the electrolyte, charge separation can be effectively promoted and photocurrent density can be dramatically increased.

A Route to Phase Controllable Cu2ZnSn(S1-xSex)4 Nanocrystals with Tunable Energy Bands

Cu2ZnSn(S1−xSex)4 nanocrystals are an emerging family of functional materials with huge potential of industrial applications, however, it is an extremely challenging task to synthesize Cu2ZnSn(S1−xSex)4 nanocrystals with both tunable energy band and phase purity. Here we show that a green and economic route could be designed for the synthesis of Cu2ZnSn(S1−xSex)4 nanocrystals with bandgap tunable in the range of 1.5–1.12 eV. Consequently, conduction band edge shifted from −3.9 eV to −4.61 eV (relative to vacuum energy) is realized. The phase purity of Cu2ZnSn(S1−xSex)4 nanocrystals is substantiated with in-depth combined optical and structural characterizations. Electrocatalytic and thermoelectric performances of Cu2ZnSn(S1−xSex)4 nanocrystals verify their superior activity to replace noble metal Pt and materials containing heavy metals. This green and economic route will promote large-scale application of Cu2ZnSn(S1−xSex)4 nanocrystals as solar cell materials, electrocatalysts, and thermoelectric materials.

Effect of ZnS and CdS coating on the photovoltaic properties of CuInS2-sensitized photoelectrodes

This paper presents a facile route to prepare CuInS2 (CIS) as a light absorber for solar cells. CIS was effectively deposited inside the pores of the nanoporous anatase titanium dioxide photoelectrodes with a high coverage degree. The performance of the CIS-sensitized TiO2 photoelectrodes could be substantially enhanced through a sequential coating with a CdS shell and a ZnS layer via successive ionic layer adsorption and reaction (SILAR). Electrochemical impedance spectrum (EIS), cyclic voltammetry (CV), and photocurrent experiments were employed to study the effect of CdS and ZnS coating. The CdS shell provided high surface coverage to passivate surface states. The ZnS layer acted as a potential barrier which was similar to an insulating layer employed in the conventional metal–insulator–semiconductor solar cells, allowing the adjustment of the electric field and potential distribution in the interface between the electrodes and the electrolyte and suppressing the dark current, resulting in further increase in the photoresponse. We found that the thickness of the nanoporous TiO2 films had a dramatic impact on the optical response and efficiency of CIS-sensitized photoelectrodes, with the 5 μm sample performing much better than the 11 μm sample, which underlined the importance of charge (or ion) transport kinetics.

Flexible, in-plane, and all-solid-state micro-supercapacitors based on printed interdigital Au/polyaniline network hybrid electrodes on a chip

A simple and rapid fabrication method involving laser printing technology and in situ anodic electropolymerization is introduced to fabricate interdigital Au/polyaniline network hybrid electrodes on polyethylene terephthalate films for flexible, in-plane, and all-solid-state micro-supercapacitors. The as-obtained micro-supercapacitors acquire a maximum energy density of 5.83 mW h cm−3 and a maximum power density of 0.45 W cm−3 that are both comparable to or superior to the values obtained for currently available state-of-the-art planar supercapacitors/micro-supercapacitors. In addition, the micro-supercapacitors exhibit remarkably high mechanical flexibility and show a good cycling stability, with 72.7% retention of the specific capacity after 1000 cycles. Moreover, the micro-supercapacitors can be optionally connected in series or in parallel to meet the voltage and capacity requirements for a given application. Compared to traditional fabrication approaches for flexible micro-supercapacitors with an interdigital in-plane design, the method demonstrated here does not involve a complicated lithography process, toxic chemical treatments, expensive rigid template, and cumbersome fabrication of jettable and stable precursor ink, which provides a simple route for fabrication of flexible planar micro-supercapacitors with high-practicality and high-performance.

Interface engineering: Boosting the energy conversion efficiencies for nanostructured solar cells*

Nanostructured solar cells have attracted increasing attention in recent years because their low cost and ease of preparation offer unique advantages and opportunities unavailable with conventional single-crystalline solar cells. The efficiencies of this kind of solar cell largely depend on the interfacial structure owing to the large specific interface areas and the inherent high density of interface states. In this review article, strategies of interface engineering will be introduced in detail. The up-to-date progress and understanding of interface engineering and its role in influencing the efficiency of nanostructured solar cells will be discussed. Some of the representative examples of the interface engineering method will be presented wherever necessary. Continued boosting of the energy conversion efficiency for nanostructured solar cells is anticipated in the coming years and will bring this kind of solar cell to the status of commercialization.

Silver Nanowire Transparent Conductive Films with High Uniformity Fabricated via a Dynamic Heating Method.

The uniformity of the sheet resistance of transparent conductive films is one of the most important quality factors for touch panel applications. However, the uniformity of silver nanowire transparent conductive films is far inferior to that of indium-doped tin oxide (ITO). Herein, we report a dynamic heating method using infrared light to achieve silver nanowire transparent conductive films with high uniformity. This method can overcome the coffee ring effect during the drying process and suppress the aggregation of silver nanowires in the film. A nonuniformity factor of the sheet resistance of the as-prepared silver nanowire transparent conductive films could be as low as 6.7% at an average sheet resistance of 35 Ω/sq and a light transmittance of 95% (at 550 nm), comparable to that of high-quality ITO film in the market. In addition, a mechanical study shows that the sheet resistance of the films has little change after 5000 bending cycles, and the film could be used in touch panels for human-machine interactive input. The highly uniform and mechanically stable silver nanowire transparent conductive films meet the requirement for many significant applications and could play a key role in the display market in a near future.

Study on hole-transport-material-free planar TiO2/CH3NH3PbI3 heterojunction solar cells: the simplest configuration of a working perovskite solar cell

Perovskite solar cells have been widely investigated owing to their high efficiency and low production cost. The working principle of perovskite solar cells is also a hot research topic. Investigations show that either the microporous oxide layer or the hole transport material could be omitted (planar configuration vs. hole-transport-material-free configuration). However, it is not known if the configuration of perovskite solar cells could be further simplified. In this work, we report on a simple hole-transport-material-free planar heterojunction perovskite solar cell with the structure FTO/hole blocking layer (compact TiO2 film)/CH3NH3PbI3/Au. We achieved a power conversion efficiency of 10.04% under one sun illumination for this simple configuration of perovskite solar cells using high-quality planar CH3NH3PbI3 films grown by a well reproducible method. Capacitance–voltage measurements show that a built-in field aiding in taking out the photocurrent to the external circuit and suppressing the back reaction of electrons from the TiO2 to the CH3NH3PbI3 film was formed in the TiO2/CH3NH3PbI3 interface depletion region. Impedance spectroscopy measurements show that a transport resistance Rtr originating from the perovskite active layer was suppressed by a large number of photo-generated currents produced at the CH3NH3PbI3 layer under light illumination.

Visible-light-driven photocatalysts: (La/Bi + N)-codoped NaNbO3 by first principles

To improve the photocatalytic activity of NaNbO3 for water splitting, the bandgap and the band edges of NaNbO3 should be tailored to match the visible part of the solar spectrum and hydrogen and oxygen redox potentials. By analyzing the band structures of La/Bi-doped and (La/Bi + N)-codoped NaNbO3, we found that the pseudointermediate band (PIB) was formed in the bandgap in all the doped systems because of the orbital splitting of the Nb 4d induced by the dramatically enlarged O-Nb-O angles. The PIB could make the wide bandgap semiconductors absorb visible-light photons as long as it was degenerate or partially degenerate. Considering that the appropriate band edges and absorption properties, we believe that (La/Bi + N)-codoped NaNbO3 materials are promising photocatalysts for hydrogen production through water splitting under visible-light irradiation without other modifications.