Organic cation – polystyrene sulfonate polyelectrolytes as hole transporting interfacial layers in perovskite solar cells

Interfacial layers are important tools that can be used to control the band structure and performance of perovskite solar cells, however, relatively few p-type materials are known compared to n-type interfacial materials. In this work, we demonstrate that anionic polystyrene sulfonate (PSS) polyelectrolytes, with organic cations as counter ions, are able to function as p-type interfacial layers in methylammonium lead triiodide (MAPbI₃) perovskite solar cells. These polyelectrolytes show interfacial dipole formation resulting in a significant increase in the work function of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and decrease in the Fermi energy of the CH₃NH₃PbI₃ layer (band bending) as evident from x-ray photoelectron spectra (XPS) and ultraviolet photoelectron spectra (UPS) analysis. These effects result in superior electron blocking and hole extracting characteristics at the anode. We show that open circuit voltage, power conversion efficiency and other device parameters can be increased compared to the devices without interfacial layers using these convenient polyelectrolytes.