Degradation of perovskite solar cells

What is it about?

We have studied a type of solar-cell made from a new class of material called perovskites. Although perovskite based solar cells are known to convert sunlight into electrical power with very high efficiency, they can also loose this efficiency with time in a process termed degradation. We have fabricated a series of solar cells, and have explore the critical factors involved in their degradation. Our tests involved running devices under a bright lamp for several hundred hours to follow their efficiency, and also exploring changes in the structure of the various materials used in the device as they age. We conclude that one of the materials used in the devices to help extract electrical current, probably trapped low levels of moisture. This trapped moisture most likely diffused into the perovskite layer over time and contributed to its degradation, making the solar cell devices loose efficiency. The most stable devices that we made lasted almost 300 hours; finding ways to extend their operational lifetime will be critical if they are going to be a practical technology.

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Why is it important?

Perovskite solar cells could be very important in a range of technologies, and could be used to generate sustainable electricity at very low cost. However understanding the practical considerations necessary to make a technology fit for real world applications is important. Here, a full understanding of the factors that cause device degradation is critical. Our measurements have shown that while certain perovskite device architectures can be efficient, some of the materials used in such devices can contribute to the degradation of the device - in particular by trapping moisture. Indeed, we believe that materials that are hydrophobic (and repel moisture) will have better stability when used as materials to extract electrical current from a perovskite solar cell as they are less likely to trap moisture. Our work confirms that it is necessary to consider each layer in a solar cell device, and understand how it contributes to the overall device stability. We have recently identified replacement materials to extract electrical current that do not trap moisture, and have been able to extend device lifetime significantly.

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