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

Abstract

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.

Comprehensive Performance Calibration Guidance for Perovskites and Other Emerging Solar Cells

“…In addition, these considerable ambiguities make it difficult to conduct meaningful efficiency comparison between different cell architectures and technologies. More and more researchers [7,8,13,[40][41][42][43][44][45][46] have advocated that the measured cell efficiency should not be determined by fast I-V scans; rather, it should represent the stabilized or steady-state performance of the device under test. Nowadays, all accredited PV testing labs in the world that report efficiencies for publication in the Progress in Photovoltaics solar cell efficiency tables [22] have adopted steady-state efficiency calibration protocols to replace the inaccurate "transient" efficiency calibration from fast I-V measurements.…”

“…In general, the steady-state efficiency calibration protocols can be categorized into two main techniques: [7,8,[40][41][42][43][44][45][46] the maximum power point tracking (MPPT) where a "perturb and observe" approach to continuously update the device load resistance is used to identify the stabilized maximum-power point over a certain period of time; and the asymptotic P MAX scan where a set of voltages are chosen in the vicinity of the voltage of maximum power point of the device, V MAX , and the device is held at each voltage long enough to permit the current to stabilize and extract a steady-state P MAX with a set of stabilized I-V points. The CMP group at NREL has developed the latter approach to conduct steady-state performance calibrations for emerging solar cells since 2016.…”

“…Even though each of the two steady-state calibration methods (i.e., MPPT and Asymptotic P MAX scan) can provide a reliable comparison between different emerging solar cells, there is limited discussion in the testing community regarding the intercomparison of results from both methods. Recently, Bardizza et al [46] have comprehensively reviewed all kinds of steady-state electrical performance calibration methods adopted in different PV testing labs and illustrated the importance of measurement repeatability. Therefore, future interlab comparisons are necessary for establishing the connection between the two protocols and the reliability of comparing results between the two methods.…”

Hysteresis in hybrid perovskite indoor photovoltaics

“…To verify our observations regarding the hysteresis of halide perovskite indoor photovoltaic devices from the J–V scan analysis, we carried out the steady state measurement of maximum power point tracking as well for the corresponding devices since the latter represents accurately the performance of the device under real operating conditions [18,28].…”

How Useful are Conventional I–Vs for Performance Calibration of Single‐ and Two‐Junction Perovskite Solar Cells? A Statistical Analysis of Performance Data on ≈200 Cells from 30 Global Sources

“…In the remainder of the manuscript, we will refer to conventional I-V scans with preset voltage scan rate as "fast I-V." Changes in perovskite devices under applied voltage typically take place over minutes and sometimes much longer, leading to the well-documented dependence of the I-V curve on voltage scan rate and scan direction. [4][5][6][7][8][9][10] These findings have led to the development of so-called steady-state performance measurement techniques aiming at bringing the device to a stable steady-state condition prior to recording its current and voltage. There are essentially two types of steady-state measurements (with some authors subdividing these into finer categories and/or using the terminology of "dynamic I-V" to represent what we here call asymptotic I-V [7] ).…”