I. ENERGY CONVERSION

(1) CZTS Solar Cells
CZTS material is a compound semiconductor that uses the earth abundant elements, Cu, Zn, Sn and S, and is therefore a very promising material to produce low cost solar cells. CZTS solar cells have proven efficiencies higher than 12%. However, the current method for the fabrication of CZTS solar cells is based on vacuum deposition of Cu, Zn and Sn followed by a sulfurization treatment conducted in tube furnace in the presence of S and Se vapors, which makes the material synthesis and device fabrication low efficient and thus makes the solar cell cost high. We are developing a solution-based method to produce CZTS material as well as fabricate solar cells of CZTS, aiming to significantly lower the cost of CZTS solar cells in terms of both material synthesis and device fabrication. In addition to lowering the cost, the solution method operating at room temperature may also make the solar cell compatible with flexible substrates, and thus gain a broader range of applications.

(2) Nanoantenna Solar Cells
Nanoantenna solar cells use (1) nanostructured antennas to capture sunlight what is viewed an electromagnetic wave and (2) rectifier diodes that works for optical frequencies and convert the AC electricity to DC electricity. Our research is focused on the design of the optical antennas that can absorb sunlight highly efficiently using a commercial software package and the fabrication of the antennas using semiconductor technology combined with nanotechnology.

(3) Thermionic Solar Cells
The theme of this project is to explore a new material which has been theoretically predicted very low work function, and is therefore a promising cathode material that can be used for thermionic solar cells towards the achievement of higher efficiency than the traditional semiconductor solar cells. Our research involves synthesizing the material, fabricating solar cell devices, and investigating the solar cell performance.

 

II. ENERGY STORAGE

(1) Solid State Electrolytes
This project is to develop solid state electrolytes with high lithium ionic conductivity by computing based on the first-principle computing. Our current interest is in Garnet-Structured Solid State Electrolytes that have proven the potential of reaching a lithium ionic conductivity as high as 0.01 S/cm, which is comparable to that of liquid electrolytes widely used in lithium ion batteries at present.

(2) Lithium Ion Batteries
Lithium ion batteries have been widely used for potable electronics in view of their high energy density for electricity storage. Lithium ion batteries have also been considered as the most competitive candidate to provide power for emerging electric vehicles. However, almost all of the existing lithium ion batteries become obviously inefficient when the environment temperature falls below the freezing point and will not work at all when the temperature is down to -20 C. There are many reasons limiting the low temperature operation of lithium batteries, such as the high viscosity of electrolytes, low ion mobility, and much slow kinetic processes in electrochemical reaction at low temperatures. Our research with regard to lithium ion batteries is focused on better understanding the kinetic processes in lithium ion batteries at low temperatures and explore methods such as doping and/or adding nanostructured catalyst to the anode and cathode of battery to improve the lithium intercalation and deintercalation at low temperatures.

 

III. NANOMATERIALS AND BIO-APPLICATIONS

(1) MXene Materials
MXenes are a family of two dimensional nanomaterials which composition can be expressed with a formula MxCy (M=a transition metal, C=carbon). MXene materials possess a large specific surface area, good conductivity and excellent chemical stability, making them a promising candidate for applications in energy conversion storage and biosensors. What we are doing are to explore an effective way to synthesize MXenes with a control of the surface chemistry to thus (1) achieve low work function that will make the materials possibly be used to build thermionic solar cells converting heat generated by concentrated sunlight to electricity, and (2) use the materials as a medium to carry certain polymers for catching and detecting biomarkers towards disease diagnosis and monitoring. (Collaborator: Wang, D. – ECE)

(2) Chemiresistive Sensor Materials
Nanomaterials with manipulable surface chemistry and large specific surface area hold great potential for being used in chemiresistive sensors to achieve high sensitivity and excellent selectivity. One of the projects that are going on in our lab is to develop and optimize a nanostructured ferroelectric material for acetone sensor. This work is being collaborated with Dr. Danling Wang's lab towards the creation of a breath analyzer for the diabetic patients based on the detection of the amount of trace acetone in the exhaled breath - a non-invasive method/device as an addition to the traditional finger prick-based blood test which is however invasive, painful and very inconvenient. (Collaborator: Wang, D. – ECE)

(3) 2D Nanomaterial Biosensor for Application in Anti-Cancer Therapy
Research in this direction focuses on the development of a new sensing technique based on novel 2D material, MXene Ti3C2, for the detection of anti-cancer metabolite, 8-hydroxyctanoic acid (8-HOA). (Collaborators: Wang, D. – ECE, Qian, S. – Pharmaceutical Sciences)

 

IV. COMPUTING

First-Principles-Based Simulation of the Properties of Electric Materials
This research is to simulate materials in terms of electric, optical, thermal and electrochemical properties to provide prediction for experimental investigations and enhance the understanding of experimental observations. The simulation is based on the first-principles computing that uses the Vienna Ab initio Simulation Package (VASP) and the super-computers in the NDSU Center for Computationally Assisted Science and Technology (CCAST). We currently focus on the simulation of the lithium ionic conductivity of garnet structure oxides, for example, Li7La3Zr2O12 (LLZO) - a promising solid-state electrolyte which has demonstrated a high lithium ionic conductivity on the order of 10^(-3) S/cm at room temperature. (Collaborator: Hoang, K. – Physics, NDSU CCAST)