Reversible Degradation in Hole Transport Layer-Free Carbon-Based Perovskite Solar Cells

The rationale for ambient degradation behaviors in hole transport layer (HTL)-free carbon-based perovskite solar cells (PSCs) still remains a mystery, although carbon-based PSCs have been the frontrunner among the emerging next-generation photovoltaics owing to their low cost of materials and fabrication process, as well as the exceptional durability. Herein, the long-term stability of HTL-free carbon-based PSCs (H-C-PSCs) in the ambient air environment is investigated to thoroughly understand and identify the governing chemistry during the degradation. Specifically, a reversible degradation phenomenon is observed along with an anomalous S-shape of current-voltage curves involving only reduction of fill factor (FF), almost without impact for short-circuit current density and open-circuit voltage. Furthermore, a minute-heating treatment will eliminate the reversible degradation which can be attributed to the reversible formation of intermediate hydrate at the interface between perovskite and carbon contact. This provides a new perspective for the stability issue of H-C-PSCs.