Electrospun Networks of ZnO-SnO2 Composite Nanowires as Electron Transport Materials for Perovskite Solar Cells

Abstract

Here, we report on the fabrication of one-dimensional (1D) zinc oxide-tin oxide (ZnO-SnO2, ZTO) hollow nanostructures by coaxial electrospinning followed by investigations of their electron transport properties in regular perovskite solar cells (PSCs). The as-electrospun nanowires (NWs) were obtained as core-shell nanostructures comprised of polymeric core and metal oxide precursors-polymer shell. Thermal analysis studies of the as-electrospun NWs revealed the optimum calcination temperature for complete removal of the polymer and formation of phase pure ZTO. The obtained nanostructured ZTO materials revealed a porous morphology with tubular nanostructures, i.e., NTs. The porous structure of nanoparticles, i.e., NTs in this case, is of particular interest due to the following reasons: (a) structure, particularly 1D, has a profound influence on the electron transport properties, and (b) suitable porosity helps in effective infiltration of perovskite material and hence supports better charge transport at the ZTO-perovskite interface. The nanomaterials were characterized by Fourier transform infrared (FTIR), diffuse reflectance spectroscopy (DRS), and energy dispersive X-ray spectroscopy (EDX) to confirm the presence/absence of functional groups, establish band gap energies ($E_g$), and determine the elemental compositions, respectively. The ZTO NTs were used as electron transport media in the fabrication of perovskite solar cells (PSCs) and established the structure-property (electron transport) relationships. The highest solar to power conversion efficiency (PCE) of 13.0% (average: 11.90%) was measured for the PSCs based on ZTO NTs obtained by calcination of as-electrospun NWs at 800°C. It indicates the fact that the calcination temperature influenced the structure which as a result influenced the electron transport property of the material used as ETL in PSCs.