Kebin Lin

Abstract All‐inorganic and lead‐free CsSnI 3 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 CsSnI 3 ‐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 CsSnI 3 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.

Recently, surface passivation has been proved to be an essential approach for obtaining efficient and stable perovskite light-emitting diodes (Pero-LEDs). Phosphine oxides performed well as passivators in many reports. However, the most commonly used phosphine oxides are insulators, which may inhibit carrier transport between the perovskite emitter and charge-transporter layers, limiting the corresponding device performance. Here, 2,7-bis(diphenylphosphoryl)-9,9′-spirobifluorene (SPPO13), a conductive molecule with two phosphine oxide functional groups, is introduced to modify the perovskite emitting layer. The bifunctional SPPO13 can passivate the nonradiative defects of perovskite and promote electron injection at the interface of perovskite emitter and electron-transporter layers. As a result, the corresponding Pero-LEDs obtain a maximum external quantum efficiency (EQE) of 22.3%. In addition, the Pero-LEDs achieve extremely high brightness with a maximum of around 190 000 cd/m2.

The inorganic CuSCN interlayer makes carbon-based perovskite solar cells more efficient and stable.