Inkjet printing of novel nanoparticle conductive inks for improving Silicon Solar cell performance.
Developments in the solar power industry over the past 50 years have led to improvements in both efficiency and economic viability of solar power installations. The cost of solar panels, in particular, has dropped from an average cost of 76.67 USD per Watt in 1977 to 0.74 USD per Watt in 2013. This has made solar photovoltaics (PV) more practical and attainable than ever before.
This project aims to address the major issues associated with the operation of solar cells in high ambient temperature environments for prolonged periods of time. A particular focus would be placed on the environmental conditions that can occur in desert and semi-arid environments such as those typical in Northern Africa, India, the Middle East and Australia. The majority of developing countries in Africa are located in deserts or semi-arid environments which cover 64% of Africa’s combined landmass. These dry environments are not suitable for agricultural production but are ideal for solar power generation. Countries such as Algeria, Libya, Sudan, Egypt and Ethiopia have normal solar irradiation values of up to 2500 kWhr/m2 year (i.e. 2 m2 could meet the energy use of a total electrical requirement of a typical Irish household). This is more than double Europe or North America’s average solar irradiance. The aridity and extreme solar irradiance of these areas make them perfectly suited to solar power generation.
Despite increased solar resources, deploying large scale solar power in these countries is still problematic due to high operating temperatures. Ambient temperatures can reach over 49 oC in arid environments and under these conditions, a solar panel can easily reach 100 oC. A primary cause of solar cell performance degradation and failure in desert and semi-arid environments is due to problems associated with thermal expansion/contraction. Arid regions have large diurnal temperature fluctuations with temperatures between day and night ranging between 49 °C and -18 °C. These fluctuations coupled with increased temperature due to absorption of thermal radiation cause expansion/contraction of the silicon in solar cells which can result in the breakage of the cell top contacts and interconnects between cells over time. By reducing the maximum operating temperature of solar cells by just 10°C, the life cycle of solar cells operating in these environments could potentially be doubled.
The main objective of this 6-week research project will be to investigate inkjet printing techniques for defining optimised top contact patterns for solar cells specifically designed to operate in arid and semi-arid environments. Solar cells require conductive contacts in their top surface in order to extract charge and complete the circuit. These contacts result in the familiar parallel lines we see on a solar cell if we look closely enough. The most common technique for defining these contacts is screen printing using conductive inks containing silver microparticles. This results in semi-porous lines which are subject to failure due to electromigration at elevated temperatures. The screen-printing process also imposes limitations in contact thickness which limit performance. These top contacts block light from falling on the solar cell and reduce overall efficiency. In any solar cell design, there is a trade-off between top contact design and efficiency. In this work, I will investigate the use of state of the art Inkjet printing technology available in the additive manufacturing laboratory at Trinity College Dublin to overcome some of the issues with conventional screen printing.
There are two reasons why inkjet printing is of interest for solar cell top contact design:
- Inkjet printing allows rapid prototyping of different contact geometries. The contact geometry has a large influence on the total sheet resistance compared to light lost due to shadowing.
- There are a number of novel conductive inks using silver nanoparticles, carbon nanotubes and graphene under development at Trinity College Dublin. The performance of these inks as silicon solar cell top contacts has not yet been tested.
This project brings together my interest in additive manufacturing and machine learning. I intend to develop a computer program to optimise the contact geometry, considering sheet resistance and light lost. I will then prototype the design by printing on top of conventional solar cells, which would be sourced from manufacturers in China. Using the Solar simulator in Prof. McCloskey’s lab, I will be able to directly measure the solar cell performance under standardised conditions and compare my results with state of the art technology.
This research, if successful, would make solar power installations more economically viable due to lower maintenance costs and increased efficiency. Developing countries would gain the most from this research as they are actively investing in energy infrastructure, and solar power is one of their most readily available resources. Countries such as Australia, which also receive comparable amounts of annual solar irradiance, would also benefit from the improvements in solar cell technology
Can inkjet printing and novel conductive inks be used to prototype top contact geometries which improve solar cell efficiency and operational lifetime in extreme temperature environments?
- Numerically design optimised contact geometry using Machine learning.
- Print the design using inkjet printing facilities and a range of inks.
- Use optical spectroscopy and scanning electron microscopy to quantify the performance and microstructure of the contacts.
- Test the device performance under standard conditions and at elevated temperatures in Prof. McCloskey’s Lab.
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