Metastability in performance measurements of perovskite PV devices: a systematic approach*

Performance measurements of photovoltaic devices, including metastable ones, should reflect as closely as possible the behaviour of these devices when deployed in the field, i.e. at constant illumination and fixed conditions. We review the wide-ranging behaviour observed in and previously proposed measurement solutions for perovskite solar cells (PSC) devices and further illustrate the variability during measurement with recent examples from our own experience. We propose a generic measurement protocol for PSC devices to ensure that electrical characterisation under simulated sunlight reflects real life conditions. The approach focusses on determining the steady-state maximum-power output under continuous illumination rather than relying on the I-V characteristics. Given the large variations in device behaviour, this protocol is particularly suitable in cases where a priori information about the devices under test is not available. We conclude that the approach to the electrical characterisation of PSC devices should shift from traditional I-V curves to the maximum-power output under steady-state conditions. The latter is the simplest and most reliable method to evaluate, assess and compare PSC technologies when power and efficiency reporting are required. This protocol also contributes to harmonising comparison between different calibration laboratories thus contributing to increased confidence in the results.