Light and Heat Induced Changes in Halide Perovskites

Michael McGehee^a, Andrea Bowring^a, Aryeh Gold-Parker^a, Vanessa Pool^b, Chris Tassone^b

^aStanford University, Stanford, CA 94305, United States

^bStanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory Menlo Park, 94025, United States

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Poster, Andrea Bowring, 144
Publication date: 5th February 2015

Methylammonium lead halides have demonstrated great promise as photovoltaic absorbing materials, recently achieving power conversion efficiencies over 18%. However, there haven’t been many detailed studies about the degradation mechanisms in these devices. Figuring out these mechanisms will be vital before perovskite solar cells can be widely deployed. Two key drivers for degradation are heat and light, both visible and UV. It seems that visible light will be an important factor in these materials because they exhibit many unusual light-induced phenomena that have yet to be explained and occur without UV illumination. For example, it has been shown that perovskite solar cells have slow photoconductivity responses, which cause I-V hysteresis only under illumination. In addition, wehave previously demonstrated that mixed halide perovskites such as CH₃NH₃Pb(Br_xI_1-x)₃ undergo a reversible structural transformation under constant 1-sun illumination over the course of minutes, resulting in the formation of defect states that pin the photoluminescence and open circuit voltage of devices made with this material at a lower energy, which reduces the power conversion efficiency.^[1] Both of these unusual phenomena likely involve ion migration and changes in the crystal lattice. In this work, weuse in-situ high resolution synchrotron x-ray powder diffraction to resolve tiny changes in lattice parameters that occur when methylammonium lead iodide is illuminated and/or heated. This study on light and heat-induced structural changes in the perovskite absorber are expected tohave important implications for device reliability and could possibly help explain the origin of hysteresis.

Hoke, E. T.; Slotcavage, D. J.; Dohner, E. R.; Bowring, A. R.; Karunadasa, H. I.; McGehee, M. D. Reversible photo-induced trap formation in mixed- halide hybrid perovskites for photovoltaics. Chem. Sci. 2014, 6, 613–617.

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