Defect-Polaron and Enormous Light-Induced Fermi-Level Shift at Halide Perovskite Surface

Alkhalifah, Ghadah; Marshall, Angelo; Rudayni, Fatimah; Wanigasekara, Shanika; Wu, Judy; Chan, Wai‐Lun

doi:10.1021/acs.jpclett.2c01940

Cited by 13 publications

(10 citation statements)

References 84 publications

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“…Recently, a series of phenomena, e.g. the significant shift of Fermi energy levels reaching the value of 700 meV [34], prolonged electron trapping and enhanced defect migration [31], have been proved by experiments in MHPs, all of which could be attributed to the formation of defect-polaron states.…”

Section: Resultsmentioning

confidence: 99%

“…For instance, the first-principles calculations predict that holeinjection and ion migration can form deep states and accelerate the nonradiative recombination due to the strong distortion of lattice [30,31]; the strong covalency at certain charge states gives rise to deep trapping levels within the band gap, which could be attributed to to the defect coupling with the distortion lattice field [32]; electrons trapping by the interstitial defects undergo the formation processes of defect-polarons in CH 3 NH 3 PbI 3 [33]. Recently, Alkhalifah et al found that the Fermi level can be shifted in a very large scale upon light illumination in halide perovskite films with excess halide vacancies, in which the formation of defect-photocarrier complex leads to lattice deformation and an energy shift of defect state [34]. They suggested that the whole process can be explained by the polaron formation at a defect site.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Polaron states of the full-configuration defects in metal halide perovskites

Liu¹,

Cui²,

Cheng³

et al. 2023

J. Phys.: Condens. Matter

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The systematical analysis for varieties of defects with diﬀerent depths and lattice relaxation strengths in metal halide perovskites (MHPs) is a challenging task. Here, we study the energy shifts of the full-conﬁguration defects due to the polaron eﬀect based on the all-coupling variational method in MHPs, where these polaron states are formed stemming from diﬀerent defect species coupling with the longitudinal optical phonon modes via Fröhlich mechanism. We ﬁnd that the polaron eﬀect results in defect levels varying from tens to several hundreds of meV, which are very close to the correction of defect levels due to the defect-polaron eﬀect, especially for these migration defects proved in the recent experiments in MHPs. These results provide the signiﬁcant enlightenment not only for analyzing the radiation and non-radiation processes of carriers mediated by defects, but also for optimizing defect eﬀect in the photovoltaic and photoelectric devices based on MHPs materials.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Polaron states of the full-configuration defects in metal halide perovskites

Liu¹,

Cui²,

Cheng³

et al. 2023

J. Phys.: Condens. Matter

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“…[37][38][39] Correspondingly, the remaining V I defects induced an upshift of CBM. [40,41] Therefore, a direct correlation was conjectured between the iodine activity and Sn 2+ autoxidation.…”

Section: Resultsmentioning

confidence: 99%

Efficient Tin Perovskite Solar Cells via Suppressing Autoxidation in Inert Atmosphere

Zhang,

Zhao,

Liu

et al. 2023

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The unsatisfactory power conversion efficiency (PCE) and long‐term stability of tin perovskite solar cells (TPSCs) restrict its further development as alternatives to lead perovskite solar cells (LPSCs). Considerable research has focused on the negative impacts of O2 and H2O, while discussions about degradation mechanism in an inert atmosphere remains insufficient. Herein, the light‐induced autoxidation of tin perovskite in nitrogen atmosphere is revealed for the first time and the elastic lattice distortion is demonstrated as the crucial role of rapid degradation. The continuous injection of photons induces energy transfer from excited A‐site cations to vibrating Sn–I framework, leading to the elastic deformation of perovskite lattice. Consequently, the over distorted Sn–I framework releases free iodine and further oxidizes Sn2+ in the form of molecular iodine. Through an appropriately designed light–dark cyclic test, a remarkable PCE of 14.41% is achieved based on (Cs0.025(MA0.25FA0.75)0.975) 0.98EDA0.01SnI3 solar cells, which is the record of hybrid triple TPSCs so far. The findings unveil autoxidation as the crux of TPSCs’ degradation in an inert atmosphere and suggest the possibility of reinforcing the tin perovskite lattice towards highly efficient and stable TPSCs.

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“…[26] Since the SPV signal depends on the Fermi level and the Fermi level change under illumination in the sample, it is influenced by band bending, doping, [49] and stoichiometry in the sample. [50] Figure 1. Schematic overview of the tr-KPFM setup.…”

Section: Surface Photovoltage and Surface Photovoltage Decaymentioning

confidence: 99%

Nanoscale Surface Photovoltage Spectroscopy

Yalcinkaya,

Rohrbeck,

Schütz

et al. 2023

Advanced Optical Materials

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Understanding electron and ion dynamics is an important task for improving modern energy materials, such as photovoltaic perovskites. These materials usually have delicate nano‐ and microstructures that influence the device parameters. To resolve detailed structure–function relationships on the relevant micro‐ and nanometer length scales, the current macroscopic and microscopic measurement techniques are often not sufficient. Here, nanoscale surface photovoltage spectroscopy (nano‐SPV) and nanoscale ideality factor mapping (nano‐IFM) via time‐resolved Kelvin probe force microscopy are introduced. These methods can map nanoscale variations in charge carrier recombination, ion migration, and defects. To show the potential of nano‐SPV and nano‐IFM, these methods are applied to perovskite samples with different morphologies. The results clearly show an improved uniformity of the SPV and SPV decay distribution within the perovskite films upon passivation and increasing the grain size. Nevertheless, nano‐SPV and nano‐IFM can still detect local variations in the defect density on these optimized samples, guiding the way for further optimization.

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Defect-Polaron and Enormous Light-Induced Fermi-Level Shift at Halide Perovskite Surface

Cited by 13 publications

References 84 publications

Polaron states of the full-configuration defects in metal halide perovskites

Polaron states of the full-configuration defects in metal halide perovskites

Efficient Tin Perovskite Solar Cells via Suppressing Autoxidation in Inert Atmosphere

Nanoscale Surface Photovoltage Spectroscopy

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