Pioneering the Future of Solar Energy: an interview with Negar Naghavi
The Hi-BITS is revolutionising the photovoltaic landscape with cutting-edge research and innovation.
Among its key focus areas, Work Package 2 (WP2) is leading the development of novel back contact technologies for Cu(In,Ga)Se2 (CIGS) solar cells, aiming to boost efficiency, lower costs, and enhance sustainability.
Negar Naghavi, Research Director at CNRS
Negar Naghavi, Research Director at CNRS, leads WP2, coordinating efforts across a diverse group of experts within the Hi-BITS consortium.
In this interview, Naghavi provides insights into how WP2’s advancements are shaping the future of solar energy.
Rethinking Solar Cell Back Contacts: Why It Matters
Q: WP2 focuses on improving solar cell efficiency by changing the materials used in the back contact of the cells. Why is this change important, and how could it help make solar panels more efficient and cost-effective?
Naghavi: The traditional back contacts in CIGS solar cells, such as the CIGS/Mo interface, have significant drawbacks, including low reflectivity and high surface recombination. These factors limit the ability of the solar cell to generate and collect charge carriers effectively, reducing overall efficiency.
Our approach involves using a transparent or reflective, passivated back contact, which brings two major improvements. Firstly, it reduces surface recombination, allowing for better charge carrier collection and higher open-circuit voltage (Voc). Secondly, the enhanced reflectivity of the back contact bounces light back into the cell, making it possible to generate more charge carriers even with a thinner absorber layer. Together, these changes allow us to use thinner and less graded absorbers, which are cheaper to produce while significantly boosting the cell’s efficiency.
Bifacial Solar Cells: Efficiency Across All Conditions
Q: Regarding the development of special transparent layers for the back of the solar cells, how do these new materials improve both the efficiency and durability of the solar panels, especially under different weather conditions?
Naghavi: Replacing the opaque molybdenum back contact with a transparent layer opens the door for bifacial solar cells, which can capture sunlight from both the front and rear sides. This feature significantly improves efficiency, particularly in environments with high ground reflectivity, such as snowy, sandy, or watery areas.
For example, the high albedo from snow-covered ground can dramatically increase rear-side illumination, boosting performance. These cells also perform well in overcast or diffuse light conditions, ensuring continued energy generation without direct sunlight. Moreover, the frameless or elevated designs used in bifacial modules enhance airflow around the panels, reducing overheating in hot climates. Altogether, these advancements maximise energy output while ensuring adaptability to diverse geographical and environmental conditions.
“By replacing traditional back contacts with transparent or reflective, passivated designs, we’re not only enhancing solar cell efficiency but also paving the way for thinner, more cost-effective, and sustainable technologies.”
Making Solar Cells Thinner and Smarter
Q: One goal of WP2 is to make solar cells thinner while keeping them highly efficient. Could you explain how new techniques for managing light within the solar cell can help achieve this, and what advantages it might offer for future solar technologies?
Naghavi: To achieve thinner solar cells, we are leveraging advanced light management techniques like back reflection, scattering, and optical confinement. These methods effectively extend the optical path length, enabling the solar cell to absorb more light even with reduced physical thickness.
This approach allows us to design solar cells that are optically thick but electrically thin. The shorter carrier collection paths compensate for imperfections in the absorber material, ensuring high efficiency despite the reduced thickness. The result is lighter, more cost-effective solar cells that maintain excellent energy conversion rates, paving the way for new applications and greater scalability in the solar industry.
Looking Ahead
Negar Naghavi’s leadership and vision in WP2 underscore the transformative potential of innovative research within Hi-BITS. By addressing fundamental inefficiencies and pushing the boundaries of solar technology, the collaborative work of WP2 is paving the way for more sustainable and cost-effective solutions that can adapt to diverse environments and market demands.
As Hi-BITS progresses, the outcomes of WP2 promise to set new standards in photovoltaic technology, solidifying Europe’s position as a leader in renewable energy innovation.