Conductivity Analysis of a Polycaprolactone/Carbon Nanotube Composite for use in Electrospun Photovoltaics and Flexible Electronics

In recent years, conductive electrospun (ES) microfibers have gained traction for use in flexible electronics and perovskite photovoltaics. ES fibers are attractive for their large surface-area-to-volume ratio and relative strength. Conductivity in ES nanofibers has been accomplished using conductive or semiconducting polymers. Alternatively, conductivity in polymer thin films can be accomplished through addition of carbon nanotubes (CNTs) or graphene.<br/><br/>Previously, we formed hybrid perovskite crystals encased in ES fibers <i>in situ </i>that demonstrated improved stability in humid conditions. In other work, we used melt electrospinning to produce conductive graphene-doped polymer fibers. Additionally, we have utilized the previously established method of multiwalled CNT (MWCNT) dispersion by combined use of a hydroxy-functionalized and unfunctionalized MWCNT blend in polycaprolactone (PCL) matrix to fabricate a conductive PCL/MWCNT composite. Thin films of the composite were measured using a four-point probe and demonstrated a maximum conductivity of 0.3765 S/cm. In the present work, the hydroxy-functionalized and unfunctionalized MWCNTs will be replaced with hydroxy functionalized and unfunctionalized metallic single-wall carbon nanotubes (MSWCNTs) to achieve larger conductivity values in the composite material in preparation for electrospinning of a multi-layer solar cell structure.<br/><br/>Triaxial ES will be used to form the multi-layer solar cell structure described. In the design, a conductive PCL core will be coated with the previously established perovskite-polymer composite. The exterior layer of the solar cell fiber structure will consist of a polymeric electron transport layer (ETL). In this work, each layer of the device will be characterized. Conductivity of a PCL thin-film doped with a mixture of functionalized and unfunctionalized MSWCNTs will be evaluated for conductivity via a non-destructive four-point probe method. Conductivity characterization will be used to determine the percolation threshold and preferable ratios for the MSWCNT-doped PCL composite used as the core of the functional fibers proposed. MSWCNT dispersion in the composite as a function of sonication time will be characterized through crystallinity analysis via Raman spectroscopy and electron microscopy.<br/><br/>Presented work will include conductivity characterization of the PCL/MSWCNT composite material and fabrication methods of a four-layer thin film photovoltaic system consisting of the conductive MSWCNT/PCL composite, a polymer-encapsulated hybrid perovskite layer, a polymeric ETL, and a transparent conductor. This work will provide the foundational preliminary data for future fabrication of an ES perovskite solar cell. The design is achieved without a hole transport layer, which has previously been established as non-consequential to perovskite solar cell performance. After adequate conductivity is achieved, the conductive ES nanofibers will be used as a central electrode in a concentric, triaxial ES photovoltaic cell.