The interfacial embedding of halogen-terminated carbon dots produces highly efficient and stable flexible perovskite solar cells

Organic-inorganic hybrid perovskite films made by low-temperature solution processing offer promising opportunities to fabricate flexible solar cells while formidable challenges regarding their environmental and mechanical stability remain due to their ionic and fragile nature. This work explores the possibility of chemical crosslinking between adjacent grains by the interfacial embedding of laser-derived carbon dots with halogen-terminated surfaces to improve the flexibility and stability of the polycrystalline films. A series of halogen-terminated carbon dots was generated in halobenzene solvents by pulsed laser irradiation in the liquid, and were then placed in the surface and grain boundaries of the perovskite film by an antisolvent procedure, where an immiscible solvent was poured onto the coating surface with a suspension containing carbon dots and perovskite precursors to cause precipitation. Strong interaction between perovskite and the carbon dots results in effective defect passivation, lattice anchoring and a change in the carrier dynamics of the perovskite films. Because of this, unencapsulated flexible perovskite solar cells after the interfacial embedding have power conversion efficiencies up to 20.26%, maintain over 90% of this initial value for 90 days under a relative humidity of 40% and have a thermal stability of 200 h even at 85 °C. The flexible devices withstand mechanical deformation, retaining over 80% of their initial values after 500 bend cycles to a radius of curvature of 4 mm.