Single-step, Atmospheric Pressure Chemical Vapor Deposition of Methylammonium Bismuth Iodide Thin Films

Author

Xiao Chen, Washington University in St. LouisFollow

ORCID

https://orcid.org/0000-0001-8245-2737

Date of Award

Summer 8-17-2017

Author's Department

Mechanical Engineering & Materials Science

Degree Name

Master of Science (MS)

Degree Type

Thesis

Abstract

Lead halide perovskites (CH₃NH₃PbI₃ and its variants) are promising solar cell absorber materials. Though the reported power conversion efficiencies of lead halide perovskite solar cells (up to 21%) are competitive with commercial silicon solar cells, lead toxicity in these perovskites present a challenge to further scale-up and eventual commercialization. Recently, bismuth (Bi³⁺) based organic halide perovskite has drawn attention as a substitution for lead-free perovskites, since it is a non-toxic 6p-block element, isoelectronic with Pb²⁺. Methylammonium bismuth iodide ((CH₃NH₃)₃Bi₂I₉) is reported for its non-toxic constituents and favorable optical band gap, thus making it a promising light absorber material. However, manufacturing ready, scale-up processes have not been developed for this compound and this presents a significant roadblock in integrating low-cost, non-toxic Bi-based perovskites into modern solar cell devices. Here, we report a single step, atmospheric pressure, chemical vapor deposition (CVD) process for (CH₃NH₃)₃Bi₂I₉. Atmospheric CVD addresses the need for rapid deposition across large area substrates, thus making the deposition of (CH₃NH₃)₃Bi₂I₉ thin films manufacturing-scalable. The precursors used are bismuth iodide (BiI₃) and methylammonium iodide (CH₃NH₃I) which are sublimated and subsequently deposited inside a tube furnace reactor with a well-controlled temperature profile. Extensive characterization is conducted via grazing incidence X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, UV-vis spectroscopy and variable temperature Hall measurements. Structural and electronic stability of (CH₃NH₃)₃Bi₂I₉ films in ambient are measured and degradation mechanisms elucidated.

Language

English (en)

Chair

Parag, Banerjee

Committee Members

Bryce Sadtler Srikanth Singamaneni

Comments

Permanent URL: https://doi.org/10.7936/K72V2FHB