Xiaoyi Li

Flexible quantum dot-sensitized solar cells employing CoS nanorod arrays/graphite paper as effective counter electrodes

We present a flexible solar cell which is composed of cobalt sulfide (CoS) nanorod arrays (NRAs) on graphite papers (GPs) (CoS NRAs/GP) as the counter electrode and CdS/CdSe quantum dot sensitized ZnO NRAs (CdS/CdSe@ZnO NRAs) as the photoanode. Orderly ZnO NRAs were directly fabricated on the flexible ITO/PET substrate by a hydrothermal method and CdS and CdSe quantum dots were subsequently deposited on them by chemical liquid deposition. CoS NRA/GP hybrid electrodes showed much higher electrocatalytic activity, higher exchange current density, and lower charge transfer resistance toward the reduction of Sx2− ions compared to Pt and GP electrodes and they exhibited superior performance when functioning as counter electrodes (CEs) in CdS/CdSe quantum dot-sensitized solar cells (QDSSCs), 400–500% better than that with Pt and GP as counter electrodes. An absolute energy conversion efficiency of 2.70% has been demonstrated for the QDSSC employing an optimized CoS NRA/GP hybrid electrode, which was relatively higher than those of the QDSSCs featuring Pt (0.52%) and GP (0.71%) CEs. This work not only provides a hybrid electrode with high catalytic activity for QDSSCs, but also demonstrates a cost-effective way to fabricate flexible electrodes that can be applied in dye-sensitized solar cells or super capacitors.

Enhancing Light Emission of ZnO‐Nanofilm/Si‐Micropillar Heterostructure Arrays by Piezo‐Phototronic Effect

n-ZnO nanofilm/p-Si micropillar heterostructure light-emitting diode (LED) arrays for white light emissions are achieved and the light emission intensity of LED array is enhanced by 120% under -0.05% compressive strains. These results indicate a promising approach to fabricate Si-based light-emitting components with high performances enhanced by the piezo-phototronic effect, with potential applications in touchpad technology, personalized signatures, smart skin, and silicon-based photonic integrated circuits.

Full Dynamic-Range Pressure Sensor Matrix Based on Optical and Electrical Dual-Mode Sensing

A pressure-sensor matrix (PSM) with full dynamic range can accurately detect and spatially map pressure profiles. A 100 × 100 large-scale PSM gives both electrical and optical signals by itself without applying an external power source. The device represents a major step toward digital imaging, and the visible display of the pressure distribution covers a large dynamic range.

Tuning Light Emission of a Pressure-Sensitive Silicon/ZnO Nanowires Heterostructure Matrix through Piezo-phototronic Effects

Based on white light emission at silicon (Si)/ZnO hetrerojunction, a pressure-sensitive Si/ZnO nanowires heterostructure matrix light emitting diode (LED) array is developed. The light emission intensity of a single heterostructure LED is tuned by external strain: when the applied stress keeps increasing, the emission intensity first increases and then decreases with a maximum value at a compressive strain of 0.15-0.2%. This result is attributed to the piezo-phototronic effect, which can efficiently modulate the LED emission intensity by utilizing the strain-induced piezo-polarization charges. It could tune the energy band diagrams at the junction area and regulate the optoelectronic processes such as charge carriers generation, separation, recombination, and transport. This study achieves tuning silicon based devices through piezo-phototronic effect.

Visualization Recording and Storage of Pressure Distribution through a Smart Matrix Based on the Piezotronic Effect

Pressure sensors that can both directly visualize and record applied pressure/stress are essential for e-skin and medical/health monitoring. Here, using a WO3 -film electrochromic device (ECD) array (10 × 10 pixels) and a ZnO-nanowire-matrix pressure sensor (ZPS), a pressure visualization and recording (PVR) system with a spatial resolution of 500 µm is developed. The distribution of external pressures can be recorded through the piezotronic effect from the ZPS and directly expressed by color changes in the ECD. Applying a local pressure can generate piezoelectric polarization charges at the two ends of the ZnO nanowires, which leads to the tuning of the current to be transported through the system and thus the color of the WO3 film. The coloration and bleaching process in the ECD component show good cyclic stability, and over 85% of the color contrast is maintained after 300 cycles. In this PVR system, the applied pressure can be recorded without the assistance of a computer because of the color memory effect of the WO3 material. Such systems are promising for applications in human-electronic interfaces, military applications, and smart robots.

A self-powered system based on triboelectric nanogenerators and supercapacitors for metal corrosion prevention

As water covers most of the earths surface, the energy of the ocean is abundant and almost unexplored, which can be one of the most environmentally friendly forms of energy. Prevention of metal corrosion plays an important role in national economic development and daily life. Here, we report a network of triboelectric nanogenerators (TENGs) and supercapacitors (SCs), which is also called the self-powered system, to harvest a huge amount of water energy for preventing metal corrosion. When the TENG is integrated with a SC, the output current is stable and continuous. The corrosion results indicate that the TENG-SC self-powered system can prevent about 80% degree of corrosion for Q235 steel in 0.5 M NaCl solution. This work demonstrates that the TENG-SC system, which is self-powered, flexible and environmentally friendly, can harvest and store large-scale blue energy from the ocean, and also renders an innovative approach toward preventing the metal corrosion without other power sources.

A Highly Stretchable Transparent Self‐Powered Triboelectric Tactile Sensor with Metallized Nanofibers for Wearable Electronics

Recently, the quest for new highly stretchable transparent tactile sensors with large-scale integration and rapid response time continues to be a great impetus to research efforts to expand the promising applications in human-machine interactions, artificial electronic skins, and smart wearable equipment. Here, a self-powered, highly stretchable, and transparent triboelectric tactile sensor with patterned Ag-nanofiber electrodes for detecting and spatially mapping trajectory profiles is reported. The Ag-nanofiber electrodes demonstrate high transparency (>70%), low sheet resistance (1.68-11.1 Ω □-1 ), excellent stretchability, and stability (>100% strain). Based on the electrode patterning and device design, an 8 × 8 triboelectric sensor matrix is fabricated, which works well under high strain owing to the effect of the electrostatic induction. Using cross-locating technology, the device can execute more rapid tactile mapping, with a response time of 70 ms. In addition, the object being detected can be made from any commonly used materials or can even be human hands, indicating that this device has widespread potential in tactile sensing and touchpad technology applications.

A nanowire based triboelectric nanogenerator for harvesting water wave energy and its applications

The ocean wave energy is one of the most promising renewable and clean energy sources for human life, which is the so-called “Blue energy.” In this work, a nanowire based triboelectric nanogenerator was designed for harvesting wave energy. The nanowires on the surface of FEP largely raise the contacting area with water and also make the polymer film hydrophobic. The output can reach 10 μ A and 200 V. When combined with a capacitor, an infrared emitter, and a receiver, a self-powered wireless infrared system is fabricated, which can be used in the fields of communication and detecting.

Flexible Light Emission Diode Arrays Made of Transferred Si Microwires-ZnO Nanofilm with Piezo-Phototronic Effect Enhanced Lighting

Due to the fragility and the poor optoelectronic performances of Si, it is challenging and exciting to fabricate the Si-based flexible light-emitting diode (LED) array devices. Here, a flexible LED array device made of Si microwires-ZnO nanofilm, with the advantages of flexibility, stability, lightweight, and energy savings, is fabricated and can be used as a strain sensor to demonstrate the two-dimensional pressure distribution. Based on piezo-phototronic effect, the intensity of the flexible LED array can be increased more than 3 times (under 60 MPa compressive strains). Additionally, the device is stable and energy saving. The flexible device can still work well after 1000 bending cycles or 6 months placed in the atmosphere, and the power supplied to the flexible LED array is only 8% of the power of the surface-contact LED. The promising Si-based flexible device has wide range application and may revolutionize the technologies of flexible screens, touchpad technology, and smart skin.