Dr Carolin Ulbrich and Dr Mark Khenkin analyzed four years of operational data, revealing that perovskite solar cells maintain excellent efficiency in summer but experience notable declines during the winter. The team presented their findings in the journal Advanced Energy Materials, marking the longest continuous outdoor evaluation of perovskite photovoltaics to date.
Under standard test conditions, lab-scale perovskite cells have reached efficiencies up to 26.95%. While commercial versions are emerging, understanding real-world performance is essential for long-term deployment. HZB, together with the University of Ljubljana through the TAPAS project, established an outdoor rack system to monitor encapsulated perovskite cells year-round. The cells, fabricated by Eva Unger's group, include a stack with ITO | 2PACz | Cs0.15FA0.85PbI2.55Br0.45 (band gap 1.65 eV) | C60 | SnO2 | Cu.
The data show that peak output held steady across the first two summers, dropping only 2% between years one and four. However, efficiency declined roughly 30% during winter seasons. Researchers attribute this to seasonal changes in sunlight spectrum at Berlin's latitude, where blue light dominates in summer and red light in winter. Since perovskite materials convert blue wavelengths more efficiently, this spectral shift impacts their performance.
"Perovskite solar cells differ from conventional PV technologies in that their efficiency often changes reversibly within the day-night cycle," explained Mark Khenkin. "This dynamic contributes significantly to seasonal variability."
Doctoral student Marko Remec led the data evaluation, contributing vital insights into how environmental conditions affect emerging solar technologies in practical use.
Research Report:Seasonality in Perovskite Solar Cells: Insights from 4 Years of Outdoor Data
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