Comprehensive Performance Calibration Guidance for Perovskites and Other Emerging Solar Cells

Abstract

have also shown remarkable efficiency improvements from ≈10% in 2017 to the latest confirmed efficiency records of 18.2% and 18.1%, respectively. [1,2] Despite the progress, researchers [3][4][5][6][7][8] have argued that many reported efficiencies in journals are being incorrectly measured, which can lead to controversies in efficiency comparison, and damage the credibility and long-term development of this field. The most common cause of efficiency ambiguity is related to the electrical I-V measurement procedure. For conventional crystalline Si cells, a current-voltage (I-V) scan is usually carried out with short dwell times from milliseconds (hereafter termed "flash I-V") to seconds (hereafter termed "fast I-V"). It is a very robust method to extract device efficiencies for Si PV and has been included in the ASTM and IEC standards [9,10] for both PV cell and module performance measurements. However, adoption of this protocol for emerging PV technologies causes efficiency ambiguity due to variable forms of electrical behaviors, mostly relating to the I-V sweep setup (i.e., scan rate and direction) and preconditioning requirements like lightsoaking. [4][5][6][7][8] For instance, hysteresis behaviors in fast I-V scans are often seen in perovskite solar cells, as shown in Figure 1. The I-V curves differ between the forward and reverse scan directions and the degree of discrepancy typically varies with the scan rate and/or preconditioning. It is therefore difficult to conduct meaningful efficiency comparisons between different emerging PV device architectures using conventional fast I-V scans. What is more important is that these controversial performance results may sacrifice confidence on future emerging PV deployment in the renewable energy portfolio. Alternatively, measurement protocols that drive the cell to steady-state provide a reliable and reproducible way to calibrate efficiencies and help all interest groups set up benchmarks for performance comparison and technology advancement. A detailed discussion on the steady-state performance calibration protocol will be presented in Section 2.3 and is the main scope of this paper.Prior to discussing steady-state performance measurements and in the interest of providing a comprehensive calibration protocol for emerging PV, we also briefly discuss two important aspects of the performance measurement sequence: the area definition and the spectral response measurement. Poorly defined device areas [11,12] result in a common measurement error and are discussed in Section 2.1. Given the small sizes

Rear Interface Engineering to Suppress Migration of Iodide Ions for Efficient Perovskite Solar Cells with Minimized Hysteresis

“…Due to the sensitivity of J – V curves to scan rate, scan direction, and light soaking, the MPPT method is normally used to validate the real performance of PvSCs. [ 45 ] From Figure 1c, the MPPT efficiency of the NdCl 3 ‐IL device is estimated to be 22.07% at 0.98 V bias, where the control gives an efficiency of 18.69% at 0.92 V bias. The more significant mismatch between reverse‐scanned J – V and MPPT efficiencies of the control device could be due to the more severe hysteresis behavior.…”

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

“…Finally, our benchmark measurement that we take to represent the true performance of the device at steady-state is the Asymptotic P MAX scan because this method has been found to produce highly reliable results. [7,8,16,17] As mentioned above, other steady-state measurement methods, such as MPPT, are also valid for performance rating of perovskite PV. Ultimately, the results we present below would have to be augmented to include comparison of fast I-V with other steady-state measurements in the perovskite and emerging PV community.…”

“…For the purpose of obtaining low-uncertainty calibrations of the complete I-V curve, the results presented here and elsewhere confirm the crucial role of stabilized measurements of slowresponding devices such as the perovskites. [3][4][5][6][7][8][9][10][11] Nonetheless, fast I-Vs do still have utility in this application, for providing a starting point for the V max search in the stabilized measurement, and for checking for whether degradation occurred during the stabilized scan by doing fast I-Vs before and after. [8,16,17] .…”

“…[3][4][5][6][7][8][9][10][11] Nonetheless, fast I-Vs do still have utility in this application, for providing a starting point for the V max search in the stabilized measurement, and for checking for whether degradation occurred during the stabilized scan by doing fast I-Vs before and after. [8,16,17] .…”

“…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] ).…”