Investigation of Structural and Electronic Properties of CH3NH3PbI3 Stabilized by Varying Concentrations of Poly(Methyl Methacrylate) (PMMA)

Celline Awino,Thomas Sakwa,Bernd Rech,Thomas Dittrich,Victor Odari,Pongthep Prajongtat

doi:10.3390/coatings7080115

Abstract

Studies have shown that perovskites have a high potential of outdoing silicon based solar cells in terms of solar energy conversion, but their rate of degradation is also high. This study reports on improvement on the stability of CH3NH3PbI3 by passivating it with polymethylmethacrylate (PMMA). Structural and electronic properties of CH3NH3PbI3 stabilized by polymethylmethacrylate (PMMA) were investigated by varying concentrations of PMMA in the polymer solutions. Stability tests were performed over a period of time using modulated surface photovoltage (SPV) spectroscopy, X-ray diffraction (XRD), and photoluminescence (PL) measurements. The XRD patterns confirm the tetragonal structure of the deposited CH3NH3PbI3 for every concentration of PMMA. Furthermore, CH3NH3PbI3 coated with 40 mg/mL of PMMA did not show any impurity phase even after storage in air for 43 days. The Tauc gap (ETauc) determined on the basis of the in-phase SPV spectra was found in the range from 1.585 to 1.62 eV for the samples stored during initial days, but shifted towards lower energies as the storage time increased. This can be proposed to be due to different chemical reactions between CH3NH3PbI3/PMMA interfaces and air. PL intensity increased with increasing concentration of PMMA except for the perovskite coated with 40 mg/mL of PMMA. PL quenching in the perovskite coated with 40 mg/mL of PMMA can be interpreted as fast electron transfer towards the substrate in the sample. This study shows that, with an optimum concentration of PMMA coating on CH3NH3PbI3, the lifetime and hence stability on electrical and structural behavior of CH3NH3PbI3 is improved.

Highlights

Hybrid organic inorganic perovskite (HOIP), for example, methylammonium lead triiodide (CH3 NH3 PbI3 ) possesses several properties such as high absorption coefficient [1], long carrier diffusion length [2], ambipolar charge transport [3], high mobility [4], as well as the ability to be solution processed via a low temperature deposition method
We successfully demonstrated that polymethylmethacrylate (PMMA) can be used to stabilize CH3NH3PbI3 due to its hydrophilic nature which helps to inhibit intrusion of moisture to stabilize CH3 NH3 PbI3 due to its hydrophilic nature which helps to inhibit intrusion of moisture into the perovskite layer
An optimum concentration of 40 mg/mL of PMMA coated on the Perovskite into the perovskite layer

Summary

Introduction

Hybrid organic inorganic perovskite (HOIP), for example, methylammonium lead triiodide (CH3 NH3 PbI3 ) possesses several properties such as high absorption coefficient [1], long carrier diffusion length [2], ambipolar charge transport [3], high mobility [4], as well as the ability to be solution processed via a low temperature deposition method. Homogenous film formation is very crucial for high performance of the device since inhomogeneous film enhances recombination of charge carriers. One-step solution process, two-step sequential method, and two-step interdiffusion are the most commonly used deposition approaches with spin coating techniques. The two-step process has received considerable efficiencies—of about 15.7%—via low temperature processing [8], there is a persistent problem of non-reproducibility due to incomplete reaction of lead iodide which reduces device performance

Methods

Results

Conclusion