A bifacial perovskite solar cell, which allows sunlight to reach both sides of the device, holds the potential to produce higher energy yields at a lower overall cost, according to scientists at the US Department of Energy’s National Renewable Energy Laboratory (NREL).
The dual nature of a bifacial solar cell is able to capture direct sunlight at the front and capture reflected sunlight at the back, allowing this type of device to outperform its monofacial counterpart.
“This perovskite cell can be very effective from either side,” said Kai Zhu, a senior scientist at NREL’s Chemistry and Nanoscience Center and lead author of a new paper published in the journal Joule. His co-authors from NREL are Qi Jiang, Rosemary Bramante, Paul Ndione, Robert Tirawat, and Joseph Berry. The other co-authors are from the University of Toledo.
Previous bifacial perovskite solar cell research has yielded devices that are considered inadequate compared to monofacial cells, with a current record of 26% efficiency. In fact, the NREL researchers noted, a bifacial cell should have a front-side efficiency close to the best-performing monofacial cell and a similar back-side efficiency.
Researchers have developed a solar cell where the efficiency under light from both sides is close. The efficiency measured in the front lighting lab reached above 23%. From the back light, the efficiency is about 91%-93% of the front.
Before building the cell, the researchers relied on optical and electrical simulations to determine the required thickness. The perovskite layer in front of the cell must be thick enough to absorb most of the photons from a portion of the solar spectrum, but a perovskite layer that is too thick will block the photons. At the back of the cell, the NREL team needed to determine the ideal thickness of the back electrode to minimize resistive loss.
According to Zhu, the simulations guided the design of the bifacial cell, and without that help the researchers had to experiment with making cell after cell to determine the ideal thickness. They found that the ideal thickness for a perovskite layer is about 850 nanometers. In comparison, a human hair is approximately 70,000 nanometers.
To evaluate the efficiency obtained by bifacial illumination, the researchers placed the cell between two solar simulators. Direct light is directed to the front side, while the back side receives reflected light. The efficiency of the cell increased as the ratio of reflected light to front light increased.
While researchers estimate that a bifacial perovskite solar module costs more to manufacture than a monofacial module, over time bifacial modules may be a better financial investment because they generate 10%-20% more power.
Qi Jiang et al, Optimal bifacial single-junction perovskite solar cells, Joule (2023). DOI: 10.1016/j.joule.2023.06.001
Provided by the National Renewable Energy Laboratory
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