2, Montana University System, Butte, Montana, United States
3, Montana Tech, Butte, Montana, United States
Hybrid organic-inorganic perovskites (HOIPs) have gained a great deal of notoriety for unique opto-electronic properties in addition to comparatively low production costs. Continued improvement in power conversion efficiencies of HOIP-based solar cells has also enabled tangential research into other optical devices; such as light-emitting diodes and solid-state radiation detection. A fundamental issue with HOIP based optical devices is in the inherent instability of the HOIP material itself. Environmental factors such as humidity, heat and ultra-violet light initiate degradation in HOIP material and limits lifetime and deployment of HOIP technology.
Previous work on improving stability has shown that compounding HOIP materials with polystyrene (PS) can drastically increase resilience of HOIPs in high humidity environments (RH~98%, 20 °C). Subsequently, the percolation threshold for conduction in these composite systems was determined (~ 70 wt% loading). The focus of this work is on fabrication of functional fiber mats of HOIP/PS composite media through melt electrospinning. Melt electrospinning is a solvent-less fabrication technique which utilizes an electrostatic field to draw-down a polymer melt into microfibers. The polymer itself may also act as a vehicle to carry out reactions and carry dopants through the draw-down process. Temperatures necessary to create a polymer melt from PS are in excess of the temperature at which thermal degradation occurs in the lead iodide HOIP species and its precursors. However, previous work has shown successful synthesis of HOIP microcrystals embedded in PS fibermats produced from melt electrospinning. At operating temperatures in the sealed melt chamber of the electrospinner methyl ammonium iodide degrades into methyl amine gas in addition to other organohalodic species. Methyl amine gas has been shown to act as a flux, converting HOIPs into a liquid state which then revert to a solid upon removal of the methyl amine gas. If correct this would be the first instance of the utilization of HOIPs in the liquid state during fabrication, as opposed during a post-processing step. The environment in the melt electrospinner will be investigated to determine the presence of liquid HOIP in situ and its effect on fiber morphology and functionality. Additionally, the use of secondary dopants, such as graphene, in the polymer melt will be investigated to incorporate a greater degree of functionally to melt electrospun HOIP/PS fibermats for use in opto-electronic devices.