Universal Current Losses in Perovskite Solar Cells Due to Mobile Ions

Abstract

Efficient mixed metal lead‐tin halide perovskites are essential for the development of all‐perovskite tandem solar cells, however they are currently limited by significant short‐circuit current losses despite their near optimal bandgap (≈1.25 eV). Herein, the origin of these losses is investigated, using a combination of voltage dependent photoluminescence (PL) timeseries and various charge extraction measurements. It is demonstrated that the Pb/Sn‐perovskite devices suffer from a reduction in the charge extraction efficiency within the first few seconds of operation, which leads to a loss in current and lower maximum power output. In addition, the emitted PL from the device rises on the exact same timescales due to the accumulation of electronic charges in the active layer. Using transient charge extraction measurements, it is shown that these observations cannot be explained by doping‐induced electronic charges but by the movement of mobile ions toward the perovskite/transport layer interfaces, which inhibits charge extraction due to band flattening. Finally, these findings are generalized to lead‐based perovskites, showing that the loss mechanism is universal. This elucidates the negative role mobile ions play in perovskite solar cells and paves a path toward understanding and mitigating a key loss mechanism.

Quantification of Efficiency Losses Due to Mobile Ions in Perovskite Solar Cells via Fast Hysteresis Measurements

“…As we will discuss later and as shown in previous reports, [2][3][4][5][6][7] the accumulation of ions at the perovskite/transport layer interfaces leads to band flattening even under short-circuit (SC) and maximum power point (MPP) conditions. [45] This band flattening causes accumulation of charges in the bulk of the perovskite, which, in turn, can dramatically increase the amount of nonradiative recombination and causes a reduction in efficiency. [2][3][4][5][6][7]45,46] To quantify the impact of ions on the JV characteristics, for example, to investigate the effects of optimized ion management, researchers often use the "hysteresis index" (HI ¼ PCE forward scan/PCE reverse scan).…”

“…[45] This band flattening causes accumulation of charges in the bulk of the perovskite, which, in turn, can dramatically increase the amount of nonradiative recombination and causes a reduction in efficiency. [2][3][4][5][6][7]45,46] To quantify the impact of ions on the JV characteristics, for example, to investigate the effects of optimized ion management, researchers often use the "hysteresis index" (HI ¼ PCE forward scan/PCE reverse scan). The HI was, however, recently challenged by Habisreutinger et al [47] as a poor indicator of performance improvement.…”

All‐Slot‐Die‐Coated Inverted Perovskite Solar Cells in Ambient Conditions with Chlorine Additives

“…The reduction of the performance with upscaling for the MAPbI 3 ‐based PSCs comes mainly from the decreased values of the J sc . Current loses in upscaled single cation PSCs can be caused by an accumulation of electronic charge in the active layer due to a reduction in the charge extraction efficiency [ 59 ] in an extended device geometry. The collection loss could be due to the presence of ion motion in the absorber films, which redistribute the internal fields in the devices.…”

“…The collection loss could be due to the presence of ion motion in the absorber films, which redistribute the internal fields in the devices. [ 59 ] In single cation PSCs devices, the ionic motion is caused by the presence of MA + ions, vacancies of A‐site cation, and iodine with activation energy 0.35–0.60 eV. [ 60–62 ] Our previous studies [ 63,64 ] for ion dynamics in single and multication perovskites thin films with deep level transient spectroscopy (DLTS) demonstrate four times higher concentration of ionic defect states in MAPbI 3 in comparison to the multication perovskite.…”

Recent Progress of Light Intensity‐Modulated Small Perturbation Techniques in Perovskite Solar Cells

“…There are several mechanisms reported for the cause of hysteresis in PSCs such as trapping and detrapping of electrons at the ETL/perovskite interface, migration of ions, etc. [41,42] However, the planar PSCs show more hysteresis than meso-PSCs. [43] In this section, we have discussed the effect of perovskite morphology, doping, and interface on the IMPS/ IMVS plots of planar PSCs.…”