Defects and related trap sites are generated inevitably at grain boundaries (GBs) and on surfaces of solution-processed polycrystalline perovskite films.

The plasmonic characteristic of core–shell nanomaterials can effectively improve exciton‐generation/dissociation and carrier‐transfer/collection. In this work, a new strategy based on core–shell Au@CdS nanospheres is introduced to passivate perovskite grain boundaries (GBs) and the perovskite/hole transport layer interface via an antisolvent process. These core–shell Au@CdS nanoparticles can trigger heterogeneous nucleation of the perovskite precursor for high‐quality perovskite films through the formation of the intermediate Au@CdS–PbI2 adduct, which can lower the valence band maximum of the 2,2,7,7‐tetrakis(N,N‐di‐p‐methoxyphenyl‐amine)9,9‐spirobifluorene (Spiro‐OMeTAD) for a more favorable energy alignment with the perovskite material. With the help of the localized surface plasmon resonance effect of Au@CdS, holes can easily overcome the barrier at the perovskite/Spiro‐OMeTAD interface (or GBs) through the bridge of the intermediate Au@CdS–PbI2, avoiding the carrier accumulation, and suppress the carrier trap recombination at the Spiro‐OMeTAD/perovskite interface. Consequently, the Au@CdS‐based perovskite solar cell device achieves a high efficiency of over 21%, with excellent stability of ≈90% retention of initial power conversion efficiencies after 45 days storage in dry air.

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Interface engineering is critical for achieving high-efficiency and high-stability perovskite solar cells (PSCs). Herein, a new interface engineering approachpoly(ethylene oxide) (PEO) modification of SnO 2 quantum dot (QD) film-to improve electron transport is introduced. It is found that when the PEO film is annealed over its glass-transition temperature, the ether-oxygen unshared electron pair in the PEO film activates to form a crosslinking complex with metal ions at the SnO 2 QD and perovskite interface, which triggers heterogeneous nucleation over the perovskite precursor film and is beneficial for achieving uniform and dense perovskite films. PEO is also shown to passivate the bulk defects of perovskite films and the interface defects between SnO 2 QD and perovskite, which promotes electron-transferring from the perovskite layer to cathode. PSCs based on SnO 2 QD with PEO treatment exhibit an enhanced efficiency, leading to a champion PCE of 20.23%, with good reproducibility and stability.

An improved protocol is proposed for preparation of a humiditysensitive soft actuator through the layer-by-layer assembling of weight-ratio-variable composites of sodium alginate (SA) and poly(vinyl alcohol) (PVA) into laminated structures. The design induces nonuniform hygroscopicity in the thickness direction and gives rise to strong interfacial interaction between layers, making the actuator have directional motility. A mathematical model reveals that the directional motion is driven by the chemical potential of humidity, and its energy conversion efficiency from humidity to mechanical work reaches 81.2% at 25 °C. By coating with CoCl 2 , the composite film of SA@PVA/CoCl 2 can act as a warning sign that provides reminder information to prevent people from slipping or falling by a conspicuous red sign during a high-humidity environment. When the film is involved in a bidirectional switch, it is capable of turning on/off light-emitting diodes by humidity, showing promising potential in control over humidity-dependent devices.

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