Investigation of 2D Hybrid Organic-Inorganic Perovskite Thin Films Deposited by RIR-MAPLE for Heterostructure Integration

Abstract

The power conversion efficiency of perovskite solar cells has increased significantly in the past 10 years from around 13% to over 25%. However, the most common perovskite absorber materials, three-dimensional (3D) perovskites, are challenged by moisture stability which hinders their more widespread commercialization. One approach to increase moisture stability is to incorporate a layer of hydrophobic ligands on top of the absorber layer in the form of a two-dimensional (2D) perovskites, thereby forming a 2D-on-3D heterostructure, however there are significant processing challenges. This dissertation conducts a careful investigation of n = 1 2D perovskite thin films deposited using a technique called resonant infrared, matrix-assisted pulsed laser evaporation (RIR-MAPLE) to better understand and then improve the heterostructure. The major conclusions of this work are that any halide mixing likely occurs in the 3D layer only at the heterostructure interface due to the site preferences that bromine and iodine have in the octahedra. Several supplemental processing parameters – deposition scheme, growth temperature, and solvent ratio (DMSO:MEG) – were used to successfully increase the average grain size, increase the amount of vertically oriented grains, modify the morphology, and decrease the Stokes shift in (PEA)2PbI4 thin films. Ultimately, out-of-plane conductivity in (PEA)2PbI4 thin films was successfully improved using the sequential deposition scheme, elevated growth temperature, and decreased amount of matrix solvent. The structural improvements and improved out-of-plane conductivity were also demonstrated for the heterostructure when modified processing conditions were used to deposit the 2D layer. The process-structure-property relationships investigated in this work serve as guidelines for tailoring 2D-on-3D heterostructures.