Carsten Deibel Institut für Physik Technische Universität Chemnitz Ionic Defects in Halide Perovskite Solar Cells Optik und Photonik kondensierter Materie
anode p n W 𝜀 𝑅 𝑅 s 𝑅 p perovskite cathode HTL ETL ≈ i - 𝑍 = 𝑉 𝑎 𝑐 𝐼 𝑎 𝑐 = 1 1 𝑅 p + i 𝜔 𝐶 + 𝑅 s 𝐶 + ETL HTL E x additional capacitance Cion by ion accumulation Debye double layer + - 4
(an additional one, δ, is seen in DLTS) find migration rate et by inflexion points → extrema of 1st derivative, β γ β γ 6 S. Reichert, J. Flemming, Q. An, Y. Vaynzof, J.-F. Pietschmann, C. Deibel Phys. Rev. Applied 13, 034018 (2020) MAPI-based solar cell
can be analyzed β γ δ Downloaded 01 Feb 2005 to 146.103.254.11. Redistribution subject to AIP license or copyright, see http://jap.aip.org/jap/copyright.jsp D. V. Lang, J. Phys. Appl. 45, 3023 (1974) double boxcar method with rate window t2/t1 e t(T) = 1/τ max(T) for this rate window migration rates et(T) = 1/τmax(T) 8 MAPI-based solar cell
𝟐 𝝉 𝟏 DLTS: R-DLTS: → all observed defects are ionic energy band trap level - 𝝉 𝟏 𝝉 𝟐 capture emission semiconductor defect: emission time longer then emission time, τ1 ≫ τ2 - 𝝉 𝟏 𝝉 𝟐 - ionic defect: migration back = migration forth, τ1 ≈ τ2 9 M. Futscher, C. Deibel ACS Energy Lett 7, 140 (2022)
defect assignment β → γ → (still mysterious ;-) δ → (also: why only in DLTS?) 𝑉 + I 10 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) S. Reichert, Q. An, Y. W. Woo, A. Walsh, Y. Vaynzof, C. Deibel Nature Commun. 11, 6098 (2020) Literature comparison
S. Tammireddy, S. Reichert, Q. An, A. D. Taylor, R. Ji, F. Paulus, Y. Vaynzof, C. Deibel ACS Energy Lett. 7, 310 (2022) Comparison MAPI, TripleCat, CsPbI3 • migration rates in MAPI, Triple cation, CsPbI3 are in the same range. • present in all: Pb or I • Pb requires high activation energies for vacancy formation • β likely iodide related defect, V+ I
both systems, β is likely • iodide vacancy at under-stoichiometry, confirming earlier result • could it be: iodide interstitial at over-stoichiometry? Triple cation MAPI β β
performance 19 3.04 ratio → highest power conversion efficiency → maximum change in absolute entropy of formation → minimum formation enthalpy → minimum migration enthalpy → lowest density of total ionic defects (β) ACS Energy Lett 7, 310 (2022)
is dominated by ionic rather than electronic defects – migration rates show wide distribution for each defect – different activation energies can still belong to the same ionic defect species → Meyer–Neldel rule – β is likely and dominates the ionic conductivity – MAPI stoichiometry with best solar cell performance coincided with minimum formation/migration enthalpy and lowest density of total ionic defects of β V+ I 20 - 𝝉 𝟏 𝝉 𝟐 -