Gaoshan Jing

A hybrid physical–chemical deposition process at ultra-low temperatures for high-performance perovskite solar cells

The quality of a perovskite film will directly determine the performance and stability of the corresponding perovskite solar cell. High-quality and uniform CH3NH3PbI3 films were synthesized by a new hybrid physical–chemical vapor deposition (HPCVD) process in a vacuum and isothermal environment. The reaction temperature can be accurately adjusted from 73 °C to 100 °C, with 73 °C as the lowest reaction temperature for a vapor based approach. CH3NH3PbI3 solar cells with high performance were fabricated at 82 °C to achieve a high power conversion efficiency (PCE) up to 14.7%. The unsealed champion solar cell was tested for 31 days continuously, and its efficiency could maintain 12.1%, demonstrating high effectiveness of this HPCVD process.

High-performance perovskite solar cells fabricated by vapor deposition with optimized PbI2 precursor films

The quality of a perovskite film determines the performance of a perovskite solar cell. A novel hybrid physical-chemical vapor deposition (HPCVD) method is presented to grow high-quality CH3NH3PbI3 films. These films were synthesized in a vacuum quartz tube with a constant growth temperature of 100 °C, resulting in the uniform film with grain sizes up to 800 nm and surface roughness of about RMS 17.4 nm. Combined with an optimized spin-coating process for PbI2 precursor films, a high-performance CH3NH3PbI3 solar cells power conversion efficiency (PCE) can reach up to 14.2%. When treated in a controlled harsh environment at 80 °C for 96 hours, ten solar cells maintained 78% of their initial efficiency on average, which demonstrates the effectiveness of this HPCVD method.

Single-crystalline monolayer and multilayer graphene nano switches

Growth of monolayer, bi-layer, and tri-layer single-crystalline graphene (SCG) using chemical vapor deposition method is reported. SCGs mechanical properties and single-crystalline nature were characterized and verified by atomic force microscope and Raman spectroscopy. Electro-mechanical switches based on mono- and bi-layer SCG were fabricated, and the superb properties of SCG enable the switches to operate at pull-in voltage as low as 1 V, and high switching speed about 100 ns. These devices exhibit lifetime without a breakdown of over 5000 cycles, far more durable than any other graphene nanoelectromechanical system switches reported.

Flexible Mixed-Potential-Type (MPT) NO2 Sensor Based on An Ultra-Thin Ceramic Film

A novel flexible mixed-potential-type (MPT) sensor was designed and fabricated for NO2 detection from 0 to 500 ppm at 200 °C. An ultra-thin Y2O3-doped ZrO2 (YSZ) ceramic film 20 µm thick was sandwiched between a heating electrode and reference/sensing electrodes. The heating electrode was fabricated by a conventional lift-off process, while the porous reference and the sensing electrodes were fabricated by a two-step patterning method using shadow masks. The sensor’s sensitivity is achieved as 58.4 mV/decade at the working temperature of 200 °C, as well as a detection limit of 26.7 ppm and small response time of less than 10 s at 200 ppm. Additionally, the flexible MPT sensor demonstrates superior mechanical stability after bending over 50 times due to the mechanical stability of the YSZ ceramic film. This simply structured, but highly reliable flexible MPT NO2 sensor may lead to wide application in the automobile industry for vehicle emission systems to reduce NO2 emissions and improve fuel efficiency.

Micro catalytic methane sensor on bulk quartz substrate

A micro catalytic methane sensor was designed and fabricated on a bulk quartz substrate for the first time to reduce power consumption of the sensor. This sensor was designed using finite element method (FEM) and fabricated on a bulk quartz substrate by two simple MEMS processes, lift off and high resolution screen printing. Local working temperature of the sensor can reach 550°C. Sensitivity of the sensor increases with temperatures changing from 250°C to 470°C, and the highest is 1.52 mV/vol. % CH4. At 300°C, sensitivity of this sensor is 0.77 mV / vol. % CH4 and power consumption of the pellistor pair is about 415 mW.

An ultrasensitive mercury sensor based on self-assembled graphene and gold nanoparticles on shrink polymer

Ultrasensitive trace mercury (II) micro sensor fabricated by mixed gold nanoparticle (Au NPs) and graphene suspension solution, and layer-by-layer self-assembled (LBL SA) on a shrink polymer based micro gold electrode is reported for the first time. Owing to the unique wrinkle surface structure and superior properties of modification film, performance of the LBL SA Graphene-Au NPs shrink sensor has enhanced greatly in determination of Hg (II) using anodic stripping voltammetry (ASV): compared with a shrink gold electrode without surface modification, the sensitivity is improved for about 3.7 times from 0.197 μA/ppb to 0.721 μA/ppb; compared with a same-sized sensor without surface modification nor shrink, the sensitivity is improved for over 50 times. This sensors detection limit of Hg (II) achieved 0.931 ppb with a sensitivity of 0.721 μΑ/ppb. This simple but highly sensitive sensor can be widely used in applications of on-line environmental monitoring of Hg (II).

Wafer-size free-standing single-crystalline graphene device arrays

We report an approach of wafer-scale addressable single-crystalline graphene (SCG) arrays growth by using pre-patterned seeds to control the nucleation. The growth mechanism and superb properties of SCG were studied. Large array of free-standing SCG devices were realized. Characterization of SCG as nano switches shows excellent performance with life time (>22 000 times) two orders longer than that of other graphene nano switches reported so far. This work not only shows the possibility of producing wafer-scale high quality SCG device arrays but also explores the superb performance of SCG as nano devices.

Planar structured perovskite solar cells by hybrid physical chemical vapor deposition with optimized perovskite film thickness

The thickness of perovskite absorber layer is a critical parameter to determine a planar structured perovskite solar cells performance. By modifying the spin coating speed and PbI2/N,N-dimethylformamide (DMF) solution concentration, the thickness of perovskite absorber layer was optimized to obtain high-performance solar cells. Using a PbI2/DMF solution of 1.3 mol/L, maximum power conversion efficiency (PCE) of a perovskite solar cell is 15.5% with a perovskite film of 413 nm at 5000 rpm, and PCE of 14.3% was also obtained for a solar cell with a perovskite film of 182 nm thick. It is derived that higher concentration of PbI2/DMF will result in better perovskite solar cells. Additionally, these perovskite solar cells are highly uniform. In 14 sets of solar cells, standard deviations of 11 sets of solar cells were less than 0.50% and the smallest standard deviation was 0.25%, which demonstrates the reliability and effectiveness of hybrid physical chemical vapor deposition (HPCVD) method.

Highly sensitive micro sensor with nafion coated bismuth for trace lead determination

This paper presents a highly sensitive micro sensor for trace determination of lead. The sensor consists of three microelectrodes including a working electrode, a counter electrode, and a reference electrode. On the working electrode surface of the sensor, a bismuth film was evaporated on the working electrode to enhance the sensors sensitivity and a negatively charged functional film of Nafion for cation-exchanging was deposited to reduce the interference caused by anionic substances in the solution. Compared with traditional glassy carbon electrode based heavy metal sensors, the microfabrication process endows the proposed sensor with great potential in portable heavy metal analyzer industry. Determination of Pb (II) was performed in an acetate buffer solution (0.1 M, pH 4.5) using anodic stripping voltammetry (ASV). Low limit of detection (LOD) of 2.79 ppb is obtained when detecting trace lead with the deposition time of 300 s. This simple, but highly sensitive electrochemical sensor may lead to wide applications of portable monitoring trace metal ions.

Low-cost and high-performance micro-channel integrated biosensor systems

We presented a low-cost and high performance layer-by-layer (LBL) self-assembled carbon nanotube (CNT) biosensor with TiO2 nanoparticles coated micro-channel integrated. The microfluidic channel surface is super hydrophilic after TiO2 nanoparticle deposition and is capable of automating liquid sampling. It is able to give stable and precise results by consuming only 10 μl reagent, approximately, which facilitates portable application of such devices. The detection limit of lung cancer biomarker ENO1 could be achieved as low as 0.01 fg/ml, superior to most of the existing detection studies reported.