Date of Award
Master of Science (MS)
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.
Bryce Sadtler Srikanth Singamaneni