Electrospun Networks of ZnO-SnO₂Composite Nanowires as Electron Transport Materials for Perovskite Solar Cells

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 (Eg), 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.