Haitao Zhai

Plasma-induced nanowelding of a copper nanowire network and its application in transparent electrodes and stretchable conductors

Copper nanowires (Cu NWs) have attracted increasing attention as building blocks for electronics due to their outstanding electrical properties and low cost. However, organic residues and oxide layers ubiquitously existing on the surface of Cu NWs impede good inter-wire contact. Commonly used methods such as thermal annealing and acid treatment often lead to nanowire damage. Herein, hydrogen plasma treatment at room temperature has been demonstrated to be effective for simultaneous surface cleaning and selective welding of Cu NWs at junctions. Transparent electrodes with excellent optical-electrical performance (19 O·sq–1 @ 90% T) and enhanced stability have been fabricated and integrated into organic solar cells. Besides, Cu NW conductors with superior stretchability and cycling stability under stretching speeds of up to 400 mm·min–1 can also be produced by the nanowelding process, and the feasibility of their application in stretchable LED circuits has been demonstrated.

Transparent heaters based on highly stable Cu nanowire films

In spite of the recent successful demonstrations of flexible and transparent film heaters, most heaters with high optical transmittance and low applied direct current (DC) voltage are silver nanowire (Ag NW)-based or silver grid-based. In this study, flexible and stretchable copper nanowire (Cu NW)-based transparent film heaters were fabricated through a solution-based process, in which a thin layer of hydrophobic polymers was encapsulated on the Cu NW films. The thin polymer layer protected the films from oxidation under harsh testing conditions, i.e., high temperature, high humidity, and acidic and alkaline environments. The films exhibited remarkable performance, a wide operating temperature range (up to 150 °C), and a high heating rate (14 °C/s). Defrosting and wearable thermotherapy demonstrations of the Cu NW film heaters were carried out to investigate their practicality. The Cu NW-based film heaters have potential as reliable and low-cost film heaters.

Novel fabrication of copper nanowire/cuprous oxidebased semiconductor-liquid junction solar cells

A Cu nanowire (NW)/cuprous oxide (Cu2O)-based semiconductor-liquid junction solar cell with a greatly enhanced efficiency and reduced cost was assembled. The Cu NWs function as a transparent electrode as well as part of the Cu NWs/ Cu2O coaxial structures, which remarkably benefit the charge separation. The best solar cell reached a conversion efficiency as high as 1.92% under a simulated AM1.5G illumination, which is 106 times higher than that of cells based on fluorine-doped tin oxide and Cu2O.

Semi-transparent polymer solar cells with all-copper nanowire electrodes

Transparent electrodes based on copper nanowires (Cu NWs) have attracted significant attention owing to their advantages including high optical transmittance, good conductivity, and excellent mechanical flexibility. However, low-cost, high-performance, and environmental friendly solar cells with all-Cu NW electrodes have not been realized until now. Herein, top and bottom transparent electrodes based on Cu NWs with low surface roughness and homogeneous conductivity are fabricated. Then, semi-transparent polymer solar cells (PSCs) with the inverted structure of polyacrylate/Cu NWs/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (PH1000)/Y-TiO2/poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid 3,4,5-tris(octyloxy)benzyl/PEDOT:PSS (4083)/Cu NWs/polyimide/polydimethylsiloxane are constructed; these could absorb light from both sides with a power conversion efficiency reaching 1.97% and 1.85%. Furthermore, the PSCs show an average transmittance of 42% in the visible region, which renders them suitable for some specialized applications such as power-generating windows and building-integrated photovoltaics. The indium tin oxide (ITO)- and noble metal-free PSCs could pave new pathways for fabricating cost-effective semi-transparent PSCs.

Copper nanowire-TiO2-polyacrylate composite electrodes with high conductivity and smoothness for flexible polymer solar cells

Copper nanowire (Cu NW) transparent electrodes have attracted considerable attention due to their outstanding electrical properties, flexibility and low cost. However, complicated post-treatment techniques are needed to obtain good electrical conductivity, because of the organic residues and oxide layers on the surface of the Cu NWs. In addition, commonly used methods such as thermal annealing and acid treatment often lead to nanowire damage. Herein, a TiO2 sol treatment was introduced to obtain Cu NW transparent electrodes with superb performance (13 Ω/sq @ 82% T) at room temperature within one minute. Polymer solar cells with excellent flexibility were then fabricated on the copper nanowire-TiO2-polyacrylate composite electrode. The power conversion efficiency (PCE) of the cells based on a blend of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PC61BM) reached 3.11%, which was better than the control devices that used indium tin oxide (ITO)-PET electrodes, and outperforms other Cu NW based organic solar cells previously reported. The PCE of the solar cells based on Cu NW electrodes remained at 90% after 500 cycles of bending, while the PET/ITO solar cells failed after 20 and 200 cycles, with sheet resistance of 35 and 15 Ω/sq, respectively.

‘Leaf vein’ inspired structural design of Cu nanowire electrodes for the optimization of organic solar cells

Cu nanowire electrodes have drawn lots of attention recently due to their potential applications in touch panels, organic solar cells and organic light-emitting diodes. The optimization of Cu nanowire electrodes is of great importance in improving the performance of devices based on them. The optical and electrical properties and surface coverage fractions of electrodes composed of nanowires with similar aspect ratios but different geometrical parameters (lengths and diameters) were thoroughly characterized, which enabled the optimization of Cu nanowire electrodes through structural design. Inspired by the grading structure of leaf veins, hybrid Cu nanowire electrodes composed of nanowires with similar aspect ratios but different geometrical parameters were constructed. By combining the advantages of nanowires with various diameters, hybrid Cu nanowire electrodes with improved conductivity at high optical transparency and large effective conducting areas were fabricated. These properties would effectively benefit the effective collection of charge carriers in solar cells. On the basis of these hybrid nanowire electrodes, organic solar cells with enhanced power conversion efficiency were constructed, which cast new light on the optimization of devices based on Cu nanowires.