Study of the stability of lead halide perovskite under two different fluoropolymer top coatings

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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.109

Study of the stability of lead halide perovskite under two different fluoropolymer top coatings Fatemeh Khorramshahi1, Arash Takshi1 1

University of South Florida, Tampa, USA

Abstract

In this work, lead halide perovskite photodetectors were fabricated by a laser-assisted rapid fabrication method. A microchannel was engraved on an indium tin oxide (ITO) coated polyethylene terephthalate (PET) conductive flexible substrate using a CO2 laser source. The channels were filled by methylammonium lead halide perovskite (CH3NH3PbI3) using the capillary motion of perovskite first-step method precursor. CYTOP and the low-cost commercially available FluroPel were used as a top protective coating layer to suppress the decomposition of the perovskite channel. X-ray diffraction pattern (XRD) was used to measure the stability of the perovskite. Strong humidity resistant and self-healing behavior were observed in both devices. The performance of the photodetectors was compared by measuring electrical and optical characteristics over time. This study will help in the low-cost fabrication of perovskite-based devices.

INTRODUCTION: Perovskite solar cell is the fastest developing photovoltaic technology [1, 2]. However, the stability of organic-inorganic halide perovskite has hindered its implementation for large scale applications. One of the most common perovskites, methylammonium lead iodide perovskite (CH3NH3PbI3), decomposes rapidly when exposed to humidity, heat, light, oxygen, etc. The following chemical reactions have been recognized as the responsible process for the potential initial step of the degradation of CH3NH3PbI3 due to moisture [3, 4]: CH3NH3PbI3(s) ֐ PbI2(s) + CH3NH3I(aq.) (1) CH3NH3I(aq.) ֐ CH3NH2+ + HI(aq.)

(2)

4HI(aq.) + O2 ֐ I2 (s) + 2H2O

(3)

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2HI(aq.) ֐ H2 + I2(s)

(4)

To suppress the decomposition of perovskite and improve the stability of device some strategies have been proposed such as improving film qualities [5], engineering thermally stable, water-repelling interlayers [6], and minimizing the exposure to environment by encapsulation techniques [7, 8]. Hydrophobic polymers provide a water repellant layer that does not let water molecules penetrate the perovskite layer. Poly(perfluorobutenylvinylether) (CYTOP) is one of the most common and efficient fluoropolymers that has been used for encapsulation in perovskite devices [9, 10]. Another type of fluoropolymer high contact angle thin film coating fluid is manufactured by Cytronix corporation by trade name FluoroPel [11]. This fluid is a true solution and does not carry micron-sized solids hence results in much thinner, smoother coats than fluid based on carrying suspended solids [11]. FluoroPel has sufficient adhesion even without thermal curing. O