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Perovskite solar cell boost with high temperature and bifacial designs

Perovskite solar cell boost with high temperature and bifacial designs

Technology News |
By Nick Flaherty



Researchers in the US and Switzerland have found a way to significantly improve the operational stability of perovskite solar cells at high temperatures, which is necessary for terawatt power grids.

At the same time researchers at NREL in the US have shown that perovskite solar cells can be used in a bifacial design to further boost the efficiency of the power conversion.

For the high temperature boost, the groups at EPFL, the University of Toronto, and the University of Kentucky use fluorinated aniliniums, a class of compounds used in pharmaceuticals, agrochemicals, and materials science.

The researchers incorporated fluorinated aniliniums in the interfacial passivation step of perovskite cell fabrication. This enhances the stability and performance of interfaces between different layers or materials to minimize defects, reduce charge recombination, and improve overall efficiency and stability.

Adding fluorinated aniliniums enhances the stability of PSCs by avoiding progressive ligand intercalation. This prevented the continuous penetration of ligand molecules between the layers or structures of the perovskite material, which destroys the integrity of the crystals, leading to degradation and decreased performance of PSCs.

Using this approach, the scientists achieved a certified quasi-steady-state power-conversion efficiency of 24.09% for inverted-structure cells. When they tested an encapsulated cell at a temperature of 85°C, 50% relative humidity, and 1-sun illumination, the device worked at its maximum power generation for 1560 hours (~65 days) while maintaining its functionality and efficiency.

The bifacial perovskite solar cell developed at the US Department of Energy’s National Renewable Energy Laboratory (NREL) showed a front illumination efficiency above 23%, comparable to monocrystalline silicon cells. From the back illumination, the efficiency was about 91%–93% of the front.

“This perovskite cell can operate very effectively from either side,” said Kai Zhu, a senior scientist in the Chemistry and Nanoscience Center at NREL.

Before constructing the cell, researchers relied on optical and electrical simulations to determine the necessary thickness. The perovskite layer on the front of the cell had to be sufficiently thick to absorb most of the photons from a certain part of the solar spectrum, but a perovskite layer that is too thick can block the photons. On the back of the cell, the NREL team had to determine the ideal thickness of the rear electrode to minimize resistive loss.

According to Zhu, simulations guided the design of the bifacial cell, and without that assistance the researchers would have had to experimentally produce cell after cell to determine the ideal thickness. They found the ideal thickness for a perovskite layer is around 850 nanometers. By comparison, a human hair is approximately 70,000 nanometers. 

While researchers estimate that a bifacial perovskite solar module would cost more to manufacture than a monofacial module, over time bifacial modules could end up being better financial investments because they generate 10%–20% more power.

www.epfl.ch; www.nrel.gov

 

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