How Interplay between Photo and Thermal Activation Dictates Halide Ion Segregation in Mixed Halide Perovskites

Journal Article · 20 November 2019 · ACS Energy Letters

DOI: https://doi.org/10.1021/acsenergylett.9b02265 · OSTI ID:1657796

Elmelund, Tor ^[1]; Seger, Brian  ^[2]; Kuno, Masaru  ^[3]; Kamat, Prashant V.  ^[3]

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1. Univ. of Notre Dame, IN (United States); Technical Univ. of Denmark, Lyngby (Denmark)
2. Technical Univ. of Denmark, Lyngby (Denmark)
3. Univ. of Notre Dame, IN (United States)

The halide ion mobility in mixed halide perovskite demonstrates two opposite trends in response to photo and thermal activation. While halides prefer to remain as Br-rich and I-rich domains under steady-state light irradiation of MAPbBr_1.5I_1.5 films, they prefer to remain in their stable mixed composition when kept in the dark. The activation energies as determined from the temperature-dependent rate constants are E_a,forward = 28.9 kJ mol^–1 for photoinduced segregation and E_a,reverse = 53.5 kJ mol^–1 for remixing of halides in the dark, respectively. The energy input from photoexcitation assists overcoming the dark (thermally activated) mixing to induce Br-rich and I-rich domains. This segregated state is maintained as long as the mixed halide film is irradiated continuously with visible light. The excitation intensity threshold above which segregation occurs follows a linear temperature dependence, such that phase separation occurs above I_exc = 30 μW/cm² white light at 23 °C. The threshold at 90 °C becomes higher with a minimum intensity requirement of 100 μW/cm² to induce segregation. The thermodynamic rationale behind this unusual halide mobility under photo and thermal excitation discussed here can aid in understanding the stability issues of perovskite solar cells.

• Research Organization: University of Notre Dame, IN (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division; Villum Foundation; USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division
• Grant/Contract Number: SC0014334; FC02-04ER15533; 9455
• OSTI ID: 1657796
• Journal Information: ACS Energy Letters, Vol. 5, Issue 1; ISSN 2380-8195
• Publisher: American Chemical Society (ACS)Copyright Statement
• Country of Publication: United States
• Language: English