Ar, N2, O2 and Humidity Impact on the Optical Constants of CH3NH3PbI3 Layers in the Temperature Range 40-80°C
Antonino La Magna a, Salvatore Sanzaro a, Emanuele Smecca a, Ioannis Deretzis a, Giovanni Mannino a, Alessandra Alberti a, Tsutomu Miyasaka b, Yohuei Numata b
a CNR-IMM, zona industriale strada VIII n°5, Catania, 95121, Italy
b 2Graduate School of Engineering, Toin University of Yokohama, 1614, Kuroganecho, Aoba, Yokohama 225-8503, Japan
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference Asia-Pacific Hybrid and Organic Photovoltaics (AP-HOPV17)
Yokohama-shi, Japan, 2017 February 2nd - 4th
Organizers: Tsutomu Miyasaka and Iván Mora-Seró
Poster 121
Publication date: 7th November 2016

We show that modifications of the optical constants occur in planar CH3NH3PbI3 layers well before any structural change is observed by X-ray diffraction. We demonstrate that environment and temperature are key parameters driving changes in the dielectric function and therefore the absorption coefficient. The measurements were performed in controlled atmosphere of non-reactive gas (dry Ar or N2) and reactive gas (O2 or humid air) as a function of the working temperature, in the range 40-80°C, indeed across the tetragonal-cubic transition. With respect to truly inert Ar used as benchmark to sign the thermal behavior of the material, annealing in N2 ambient not only assures the reversibility of the optical behavior during thermal cycles, thus preventing/counteracting degradation effects, but also slightly improves the optical response during time. While it is clearly elucidated that the optical constants of the material can be recovered during thermal cycles in N2 and Ar ambient, the presence of humidity in the air, instead, causes the absorption coefficient to monotonically and inexorably degrade especially at the crossover of the phase transition (above 60°C). An intermediate case is represented by the saturated O2 ambient. The appropriate use of N2 to stabilize the layer indeed results as an effective strategy to preserve the optical response of the material under thermal operation conditions

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