Insight into the CH3NH3PbI3/C interface in hole-conductor-free mesoscopic perovskite solar cells

Abstract

Perovskite solar cells (PSCs) with hole-conductor-free mesoscopic architecture have shown superb stability and great potential in practical application. The printable carbon counter electrodes take full responsibility of extracting holes from the active CH₃NH₃PbI₃ absorbers. However, an in depth study of the CH₃NH₃PbI₃/C interface properties, such as the structural formation process and the effect of interfacial conditions on hole extraction, is still lacking. Herein, we present, for the first time, an insight into the spatial confinement induced CH₃NH₃PbI₃/C interface formation by in situ photoluminescence observations during the crystallization process of CH₃NH₃PbI₃. The derived reaction kinetics allows a quantitative description of the perovskite formation process. In addition, we found that the interfacial contact between carbon and perovskite was dominant for hole extraction efficiency and associated with the photovoltaic parameter of short circuit current density (J_SC). Consequently, we conducted a solvent vapor assisted process of PbI₂ diffusion to carefully control the CH₃NH₃PbI₃/C interface with less unreacted PbI₂ barrier. The improvement of interface conditions thereby contributes to a high hole extraction proved by the charge extraction resistance and PL lifetime change, resulting in the increased J_SC valve.