Dendritic CsSnI₃ for Efficient and Flexible Near‐Infrared Perovskite Light‐Emitting Diodes

TLDR

CsSnI₃ is a promising lead‑free material for near‑infrared perovskite LEDs, but its devices suffer from hole‑electron injection imbalance that degrades performance. The study aims to balance charge injection and enhance recombination by adjusting the perovskite/charge‑transport interface. A dendritic CsSnI₃ layer is deposited on the hole‑transport material, exposing most of its surface to the electron‑transport layer, thereby enlarging the electron‑interface area and spatially confining carriers to boost radiative recombination. This architecture delivers lead‑free NIR LEDs with a record 5.4 % EQE and retains 93.4 % of the initial efficiency after 50 bending cycles, with negligible morphology change after 2000 bends.

Abstract

All-inorganic and lead-free CsSnI3 is emerging as one of the most promising candidates for near-infrared perovskite light-emitting diodes (NIR Pero-LEDs), which find practical applications including facial recognition, biomedical apparatus, night vision camera, and Light Fidelity. However, in the CsSnI3 -based Pero-LEDs, the holes injection is significantly higher than that of electrons, resulting in unbalanced charge injection, undesired exciton dissipation, and poor device performance. Herein, it is proposed to manage charge injection and recombination behavior by tuning the interface area of perovskite and charge-transporter. A dendritic CsSnI3 structure is prepared on the hole-transporter, only making a bottom contact with the hole-transporter and exposing all other available crystal surfaces to the electron-transporter. In other words, the interface area of perovskite/electron-transporter is significantly higher than that of perovskite/hole-transporter. Moreover, the embedding interface of perovskite/electron-transporter can spatially confine holes and electrons, increasing the radiation recombination. By taking advantage of the dendritic structure, efficient lead-free NIR Pero-LEDs are achieved with a record external quantum efficiency (EQE) of 5.4%. More importantly, the dendritic structure shows great superiorities in flexible devices, for there is almost no morphology change after 2000-cycles of bends, and the fabricated Pero-LEDs can keep 93.4% of initial EQEs after 50-cycles of bends.