Suppressing Cation Migration in Triple-Cation Lead Halide Perovskites

• Published in: ACS energy letters Vol. 5; no. 9; pp. 2802 - 2810
• Main Authors: Pavlovetc, Ilia M, Brennan, Michael C, Draguta, Sergiu, Ruth, Anthony, Moot, Taylor, Christians, Jeffrey A, Aleshire, Kyle, Harvey, Steven P, Toso, Stefano, Nanayakkara, Sanjini U, Messinger, Jonah, Luther, Joseph M, Kuno, Masaru
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 11-09-2020; American Chemical Society (ACS)
• Subjects: cation migration; Cations; Genetics; Perovskites; Solar cells; SOLAR ENERGY; Stability
• ISSN: 2380-8195; 2380-8195
• DOI: 10.1021/acsenergylett.0c01207

Ion migration represents an intrinsic instability of metal halide perovskite solar cells. Here we show that triple-cation FA x MA y Cs1–x–y PbI3 [FA+ = (NH2)2CH+, MA+ = CH3NH3 +] active layers with mixed orthorhombic, post-perovskite (δortho-CsPbI3), and cubic perovskite (α) phases (i.e., α/δ-phase FA x MA y Cs1–x–y PbI3) exhibit improved cation stability against applied bias relative to pure α-phase perovskites (i.e., FA0.85Cs0.15PbI3 and FA0.76MA0.15Cs0.09PbI3). Infrared photothermal heterodyne imaging and time-of-flight secondary ion mass spectrometry are used to visualize exclusive α-phase perovskite lateral device A+ cation accumulation (depletion) at perovskite negative (positive) electrode interfaces. The resulting compositional heterogeneities lead to degradation. Operational stability testing of solar cells reveals similar degradation behavior; α/δ-phase FA x MA y Cs1–x–y PbI3 lateral devices/solar cells, by contrast, show improved stabilities. Enhanced α/δ-FA x MA y Cs1–x–y PbI3 stability is rationalized by δortho-phase inclusions, acting as barriers through which A+ cations do not easily migrate. This study thus provides new insights into cation migration in FA x MA y Cs1–x–y PbI3 perovskites and suggests a materials design strategy toward suppressing cation instabilities in hybrid perovskites.