The Helmholtz-Zentrum Berlin has published the results of a four-year series of measurements of perovskite solar cells in the field. According to the results, the peak output remained almost the same in the first two summers. Between the first and fourth summer, efficiency fell by around two percent in absolute terms. In the winter months, however, efficiency fell by around 30 percent.
The research team led by Carolin Ulbrich and Mark Khenkin blames this on a change in the spectral distribution of sunlight. At higher latitudes – such as in Berlin – the sunlight contains more blue components in summer and more red components in winter. However, perovskite solar cells can primarily convert the blue components of light into electrical energy. The research team therefore assumes that perovskite solar cells at locations near the equator, where these spectral shifts are less pronounced, produce a more constant yield over the course of the year. »What distinguishes perovskite solar cells from more mature PV technologies is that they often change their efficiency reversibly in the day-night cycle; this property contributes significantly to the strong seasonal fluctuations observed,« says Khenkin.
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