Experiences of Continuous On-Sun Performance Measurements of Perovskite Mini-Modules
A set of Perovskite-based mini-modules have been distributed between testing partners in Cyprus and Germany in order to acquire performance measurements of the devices under long-term outdoor exposure. The devices were tested indoors prior to mounting outdoors where their current-voltage characteristics were recorded at regular intervals over several months using various loading and voltage sweeping strategies. All modules tested showed a decrease in power conversion efficiency over time, though subsequent discoveries have shown that this arose from some recoverable process and is not an irreversible form of degradation. A basic theory is expounded that attributes both long-term performance decline and recovery to the migration of slow-moving ionic species within the Perovskite cells. Furthermore, the same process, with faster ion migration, can explain the observed behaviour of the modules under different voltage sweep and loading strategies. This work has reaffirmed the importance of considering the movement of ions in any I-V tracing strategy and provides a set of recommendations to deal with this. While MPP loading facilitates the measurement of more representative instantaneous device efficiencies, it has not been possible to conclude that real degradation is enhanced when keeping modules at open circuit between scans.