Thermal Stability Enhancement Of Methylammonium Lead Iodide Film Passivated By Poly(Methyl Methacrylate) And Caffeine For Perovskite Solar Cell Fabrication

Soo, Yew Hang (2021) Thermal Stability Enhancement Of Methylammonium Lead Iodide Film Passivated By Poly(Methyl Methacrylate) And Caffeine For Perovskite Solar Cell Fabrication. Master dissertation/thesis, UTAR.

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Abstract

Methylammonium lead iodide (MAPbI3) is a promising perovskite material that can function as light absorbing layer in a perovskite solar cell. However, the use of organic charge transport layers (CTLs) on the MAPbI3 layer had led to device operation instability and premature failure, which hindered their commercialization. On the other hand, the emergence of inorganic CTL-based on low-temperature metal oxide sols with annealing temperature of ≤150 °C may replace these unstable organic CTLs to improve device operational stability. Nevertheless, their annealing temperature had reported to cause rapid thermal degradation of MAPbI3 film fully into lead iodide (PbI2) in ≤90 min. Here, this work prepared the MAPbI3 films using antisolvent assisted spin-coating and encapsulated it with poly(methyl methacrylate) (PMMA) via spin-coating PMMA solution in ethyl acetate on the films. These PMMA encapsulated MAPbI3 films were then stressed at 150 °C to test their thermal stability. The MAPbI3 films encapsulated by PMMA demonstrated high thermal endurance at 150 °C, whereby the MAPbI3 phase sustained from thermal degradation for 2 h and remained dominant over PbI2 phase after 5 h. Additional thermal stability was also demonstrated with the addition of caffeine as additive to the MAPbI3 film, retaining dominant MAPbI3 phase even after 24 h. This thermally stable duration window surpassed the annealing time required for the low-temperature metal oxide sols to form compact CTLs. As a proof of concept, this work spincoated vanadium oxide (VOx) sol (derived from vanadyl acetylacetonate (VO(acac)2) aged in isopropanol) on 2 mg/mL PMMA encapsulated, caffeine added MAPbI3 film and annealed the sol for 20 min to break the acetylacetonate ring for formation of VOx. The VOx sol was successfully annealed on the PMMA encapsulated and caffeine added MAPbI3 film without thermal degradation.

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