Less expensive, more flexible, more efficient – these are the advantages that solar cells based on perovskites offer compared to the previously dominant semiconductor material, silicon. Even the high efficiency of the best laboratory cells of 25.7 percent is hardly inferior to the efficiency of silicon solar cells. The lack of durability of the perovskites alone has so far slowed down serial production. But now researchers have succeeded in drastically increasing the longevity of their prototypes with an extremely thin protective layer. As they report in the journal Science, their perovskite solar cells can generate solar power for more than five years at temperatures of up to 35 degrees Celsius.
So far, the sunlight-absorbing perovskite layer and the underlying layer for transporting the electrical charge carriers have been particularly sensitive. Therefore, Yueh-Lin Loo from Princeton University and her team added a protective layer of the elements cesium, lead and iodine, only a few atoms thick, between these two layers. The so-called two-dimensional material had a strong stabilizing effect on the surrounding layers, which are particularly important for solar power generation. Initial observations have already shown that the efficiency of the perovskite solar cell has not decreased even after six months.
Loo and her colleagues then analyzed this surprising stability even more precisely by developing a kind of stress test for solar cells. “A durability of 30 years is desired, but we cannot test our cells for 30 years,” says Loo. Therefore, the researchers not only exposed their solar cells to artificial sunlight for a long time, but also heated them to high temperatures of up to 110 degrees Celsius Under these conditions, the aging process of the solar cells could be greatly accelerated.From the collected data, Loo and her team then deduced the actual service life under cooler, more realistic conditions.
The stress test showed that at temperatures of 110 degrees Celsius, the efficiency of the solar cells only dropped to around 80 percent of the original efficiency after more than 2100 hours. At 35 degrees Celsius, on the other hand, Loo and her colleagues observed hardly any loss of performance. More precise calculations showed that the solar cells achieve an amazingly long service life of more than five years at moderate temperatures. With new material variants and manufacturing processes, it is therefore possible for perovskite solar cells to be able to generate solar power with high efficiency for 20 to 30 years, according to the researchers. At the same time, the hitherto relatively low efficiency of the prototype of 17.4 percent could be further increased. There is therefore a realistic chance that in a few years pure perovskite solar cells with an efficiency of more than 20 percent or perovskite-silicon tandem cells with an efficiency of up to 30 percent can be mass-produced.