Introduction: Renewable energies are considered as only safe energy
sources that should be used in the future. The other types of energy sources
adds heat and chemicals to the environment. All these could lead to climate
changes and environmental pollutions.
Cu2ZnSnS4 (CZTS) is a promising
material that consists of earth abundant and non-toxic elements. Due to its
high light absorption coefficient, it can be 300 times thinner (1 µm) than
conventional silicon solar cells. As the material gets thinner, it becomes
flexible and opens up completely new possibilities for applications such as wearable
and easy to transport products. It is also possible to make this compound by
chemical process and printing technologies.
CZTS is usually grown on molybdenum substrate by high
temperature (~570°C) sulfurization of Cu, Zn and Sn. Molybdenum
substrate is then later used as a back contact for solar cell. There are not
many metals that are as resilient as Mo in high temperature sulfurization. Therefore,
researches involving different back contact or back surface passivation are
lift off process and back contact engineering: Laser lift off is a method that separates two layers
of material with significant bandgap difference. The high power laser pulse (25
ns duration) transmit through the transparent substrate and knocks off the thin
materials on top. Employing laser lift off process will enable us to grow CZTS
(and the subsequent cell) on different crystalline substrates and transfer the
cell on any highly reflective back contact material. Using crystalline substrates,
such as sapphire, quartz
might allow us to grow epitaxial CZTS films with fewer defects. This is a novel
technique in the field of CZTS research. Initial trials for laser lift off
process with KrF 248 nm excimer laser has been successfully made.
tandem structure: Another
advantage of laser lift off process is that it can be perfect way to make
tandem CZTS/Si solar cell. Manufacturing tandem solar cell is usually a complex
process. The main problem of integrating CZTS with silicon layer will be high
temperature sulfurization process. During this process, Cu and S can contaminate
and degrade the bottom silicon solar cell. Copper is notorious for degrading
device performance of silicon solar cells. Sulfur is also highly reactive element,
which will cause detrimental effects.
Opportunities: The main focus of this project will be on interface
between CZTS and back contact with this novel technique. Furthermore, the student
will be able to experience solar cell production process from a scratch. It is
good opportunity to learn about how physics, chemistry, and mathematical models
all connect when making solar cell in the purpose of maximizing efficiency. You have to be open minded and creative to find the ways to improve the efficiency
and explain the results.
Feel free to contact if you have questions.
Solid background in physics, creativity and passion