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Probing the Ionic Defect Landscape in Halide Perovskite Solar Cells

Carsten
October 07, 2020

Probing the Ionic Defect Landscape in Halide Perovskite Solar Cells

Mobile ions in metal halide perovskites are causing current-voltage hysteresis in solar cells, and promote degradation and non-radiative recombination. We want to contribute to the understanding of the fundamental properties of ionic transport and its relationship to processing parameters. Therefore, we characterised the ionic defect landscape of methylammonium lead triiodide (MAPbI3) perovskites with fractionally changed precursor stoichiometry [1] by impedance spectroscopy and deep-level transient spectroscopy (DLTS). I will briefly introduce these experimental methods, and how the latter allows to distinguish between electronic traps and ionic defects. With IS, we observed three different ionic defects in MAPbI3 and their migration rates and activation energies. To gain more insight, we applied a newly developed algorithm for performing inverse Laplace transform to evaluate the DLTS capacitance transients. The result reveals a broad distribution of migration rates for each of the observed ionic defect [2]. Our findings show a major impact of the precursor stoichiometry on the defect landscape, with direct consequences for the electronic properties such as the measured built-in potential and the open-circuit voltage. I will also show how we applied the Meyer-Neldel rule to categorise the migration rates of the different ionic defects and discuss where it comes from [3].

[1] P. Fassl, V. Lami, A. Bausch, Z. Wang, M.T. Klug, H.J. Snaith, and Y. Vaynzof, Fractional deviations in precursor stoichiometry dictate the properties, performance and stability of perovskite photovoltaic devices. Energy & Environmental Science 11, 3380 (2018).
[2] S. Reichert, J. Flemming, Q. An, Y. Vaynzof, J.-F. Pietschmann, and C. Deibel, Ionic-Defect Distribution Revealed by Improved Evaluation of Deep-Level Transient Spectroscopy on Perovskite Solar Cells. Phys. Rev. Applied 13, 034018 (2020).
[3] S. Reichert, Q. An, Y.-W. Woo, A. Walsh, Y. Vaynzof, and C. Deibel, Probing the ionic defect landscape in halide perovskite solar cells. arXiv 2005.06942v1 (2020).

Carsten

October 07, 2020
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  1. PERIMPED ∙ 7th October 2020 ∙ [email protected] www.tu-chemnitz.de/physik/OPKM Carsten Deibel

    Optik und Photonik kondensierter Materie Institut für Physik Technische Universität Chemnitz Probing the Ionic Defect Landscape 
 in Halide Perovskite Solar Cells
  2. PERIMPED ∙ 7th October 2020 ∙ [email protected] www.tu-chemnitz.de/physik/OPKM Probing the

    Ionic Defect Landscape 
 in Halide Perovskite Solar Cells Sebastian Reichert & Sandhya Tammireddy @ TUC Yana Vaynzof & Qingzhi An @ TU Dresden Aron Walsh & Young-Won Woo @ Imperial & Yonsei U Jan-F Pietschmann & Jens Flemming @ TUC
  3. [email protected] www.tu-chemnitz.de/physik/OPKM Capacitance in the time and frequency domain transparent

    anode p n W 𝜀 𝑅 𝑅 s 𝑅 p perovskite cathode HTL ETL ≈ i - ETL HTL E x additional capacitance Cion by ion accumulation Debye double layer 𝑍 = 𝑉 𝑎 𝑐 𝐼 𝑎 𝑐 = 1 1 𝑅 p + i 𝜔 𝐶 + 𝑅 s 𝐶 + + -
  4. [email protected] www.tu-chemnitz.de/physik/OPKM Capacitance–Voltage 1. Capacitance–voltage measurement C(V) - applying additional

    dc-voltage
 → built-in voltage Vbi and 
 effective doping density Neff transparent anode 𝜀 𝑅 𝑍 = 𝑉 𝑎 𝑐 𝐼 𝑎 𝑐 = 1 1 𝑅 p + i 𝜔 𝐶 + 𝑅 s perovskite cathode HTL ETL 𝐶 = 𝑑 𝑄 𝑑 𝑈 = 𝑒 𝜀 𝜀 0 2( 𝑉 bi − 𝑉 ) 𝑁 eff V C full depletion injection depletion capacitance - + Note of caution: 
 consider the work by Ravishankar, Unold, Kirchartz (2020), arXiv:2008.02892 (as defect concentration for DLTS dep. on ε and Neff, and on ε for impedance)
  5. [email protected] www.tu-chemnitz.de/physik/OPKM Impedance spectroscopy 1. Capacitance-voltage measurement - C(V) -

    applying additional dc-voltage !Vbi and Neff 2. Impedance spectroscopy – C(ω) - varying measurement frequency ω ! defect/ion characterisation (EA , D, Nt ) 𝑍 = 𝑉 𝑎 𝑐 𝐼 𝑎 𝑐 = 1 1 𝑅 p + i 𝜔 𝐶 + 𝑅 s 𝐶 = 𝑑 𝑄 𝑑 𝑈 = 𝑒 𝜀 𝜀 0 2( 𝑉 bi − 𝑉 ) 𝑁 eff C log( ) ω Cgeo ΔC2 ΔC1 𝑒 t2 𝑒 t1 transparent anode 𝜀 𝑅 perovskite cathode HTL ETL - +
  6. [email protected] www.tu-chemnitz.de/physik/OPKM Deep-level transient spectroscopy 1. Capacitance-voltage measurement - C(V)

    - applying additional dc-voltage !Vbi and Neff 2. Impedance spectroscopy – C(ω) - varying measurement frequency ω ! defect/ion characterization (EA , D, Nt ) 3. Deep-level transient spectroscopy (DLTS) – C(t) - applying filling pulse ! defect/ion characterization (EA , D, Nt ) + sign of defect (majority/minority, anion/cation) 𝑍 = 𝑉 𝑎 𝑐 𝐼 𝑎 𝑐 = 1 1 𝑅 p + i 𝜔 𝐶 + 𝑅 s 𝐶 = 𝑑 𝑄 𝑑 𝑈 = 𝑒 𝜀 𝜀 0 2( 𝑉 bi − 𝑉 ) 𝑁 eff t U ΔC C0 t C 𝑪 ( 𝒕 ) = 𝑪 𝟎 ± ∆ 𝑪 𝐞 𝐱 𝐩 (− 𝒆 𝐭 𝒕 ) transparent anode 𝜀 𝑅 perovskite cathode HTL ETL - +
  7. [email protected] www.tu-chemnitz.de/physik/OPKM MAPbI3 solar cells with stoichiometric variation Fassl et.al.,

    Energy Environ. Sci., 2018, 11, 3380: (Yana Vaynzof’s group)
  8. [email protected] www.tu-chemnitz.de/physik/OPKM Example: stoichiometric 1:3.00 sample β γ β γ

    δ Ionic-Defect Distribution Revealed by Improved Evaluation of Deep-Level Transient Spectroscopy on Perovskite Solar Cells S. Reichert, J. Flemming, 
 Q. An, Y. Vaynzof, 
 J. F. Pietschmann, C. Deibel Phys. Rev. Applied 13, 034018 (2020) Impedance spectroscopy Deep-level transient spectroscopy ! three defects (β,γ,δ) can be analyzed (shown: boxcar evaluation)
  9. [email protected] www.tu-chemnitz.de/physik/OPKM Arrhenius for all stoichiometries 𝑒 t = e2

    𝑁 eff 𝐷 𝑘 B 𝑇 𝜖 0 𝜖 R 𝐷 = 𝐷 0 exp(− 𝐸 A 𝑘 B 𝑇 ) with Probing the ionic defect landscape in halide perovskite solar cells S. Reichert, Q. An, Y. W. Woo, A. Walsh, Y. Vaynzof, C. Deibel arXiv:2005.06942 arXiv:2005.06942 Cite this:DOI: 10.1039/c9mh00445a Quantification of ion migration in CH3 NH3 PbI3 perovskite solar cells by transient capacitance measurements† Moritz H. Futscher, a Ju Min Lee,a Lucie McGovern,a Loreta A. Muscarella, a Tianyi Wang, a Muhammad Irfan Haider,b Azhar Fakharuddin, b Lukas Schmidt-Mende b and Bruno Ehrler *a Ion migration in halide perovskite films leads to device degradation and impedes large scale commercial applications. We use transient Received 25th March 2019, Accepted 11th April 2019 DOI: 10.1039/c9mh00445a rsc.li/materials-horizons New concepts Materials Horizons COMMUNICATION (as done before on perovskites by:)
  10. [email protected] www.tu-chemnitz.de/physik/OPKM Defect assignments classical defect: 𝝉 𝟏 ≫ 𝝉

    𝟐 ionic defect: 𝝉 𝟏 ~ 𝝉 𝟐 𝝉 𝟐 𝝉 𝟏 DLTS: R-DLTS: → all defects are mobile ions literature comparison for defect assignment (likely scenario): 
 (the signs are experimental, the rest is guesstimating) β → γ → δ → 𝑉 − 𝑀 𝐴 𝑀 𝐴 + 𝑖 𝐼 − 𝑖 energy band trap level - 𝝉 𝟏 𝝉 𝟐 capture emission arXiv:2005.06942
  11. [email protected] www.tu-chemnitz.de/physik/OPKM Distribution of migration rates Inverse Laplace transform via

    Regularized Sparse Laplace Spectrum (RegSLapS) test with synthetic data revealed equidistant peaks in solution space for decay with distributed migration rates with different methods are slightly different migrations rates of the same defect distribution detectable → possible explanation for differences in reported defect parameters in literature Phys. Rev. Applied 13, 034018 (2020)
  12. [email protected] www.tu-chemnitz.de/physik/OPKM • Yang et al., Science 356, 1376 (2017)

    • Futscher et al., Mater. Horiz. 6, 1497 (2019) • Rosenberg et al., J. Appl. Phys. 122, 145701 (2017) • Samiee et al., Appl. Phys. Lett. 105, 153502 (2014) • Xu et al., Nature Photonics 13, 418 (2019) Arrhenius comparison with literature arXiv:2005.06942
  13. [email protected] www.tu-chemnitz.de/physik/OPKM Impact on defect parameters arXiv:2005.06942

  14. [email protected] www.tu-chemnitz.de/physik/OPKM Meyer-Neldel rule with 𝐷 0 = 𝐷 00

    exp ( 𝐸 A 𝐸 MN ) ! D00 and EMN related to ionic hopping process 𝐷 = 𝐷 0 exp(− 𝐸 A 𝑘 B 𝑇 )
  15. PERIMPED ∙ 7th October 2020 ∙ [email protected] www.tu-chemnitz.de/physik/OPKM Thank you!

    impedance and DLTS are consistent minor stoichiometry changes in MAPI change the 3 ionic defects strongly → solar cell parameters defects are distributions, but Meyer–Neldel rule allows their classification @deibellab