Elimination of charge trapping at defects is highly challenging for poly-crystalline organometal halide perovskites. Here, we report a new architecture for reinforcing the built-in electric field (E_in) across the photoactive layer with a pair of strong electric dipole layers (EDLs). The paired EDLs significantly intensify the E_in across the perovskite layer, resulting in suppressed charge trapping of photogenerated charges. As a result, our low-temperature processed P–I–N planar PeSC devices using the paired EDLs exhibit a higher power conversion efficiency (η_max ∼ 19.4%) and a smaller device-to-device variation with a standard deviation (S.D.) of 0.70%, which far surpass those (η_max ∼ 17.8%, S.D. ∼ 1.1%) of the devices with typical charge transport layers.

The photoluminescence quantum yield (PLQY) and charge carrier mobility of organic–inorganic perovskite QDs were enhanced by the optimization of crystallinity and surface passivation as well as solid-state ligand exchange. The crystallinity of perovskite QDs was determined by the Effective solvent field (E_sol) of various solvents for precipitation. The solvent with high E_sol could more quickly countervail the localized field generated by the polar solvent, and it causes fast crystallization of the dissolved precursor, which results in poor crystallinity. The post-ligand adding process (PLAP) and post-ligand exchange process (PLEP) increase the PLQY of perovskite QDs by reducing non-radiative recombination and the density of surface defect states through surface passivation. Particularly, the post ligand exchange process (PLEP) in the solid-state improved the charge carrier mobility of perovskite QDs in addition to the PLQY enhancement. The ligand exchange with short alkyl chain length ligands could improve the packing density of perovskite QDs in films by reducing the inter-particle distance between perovskite QDs. The maximum hole mobility of 6.2 × 10⁻³ cm² V⁻¹ s⁻¹, one order higher than that of pristine QDs without the PLEP, is obtained at perovskite QDs with hexyl ligands. By using PLEP treatment, compared to the pristine device, a 2.5 times higher current efficiency in perovskite QD-LEDs was achieved due to the improved charge carrier mobility and PLQY.

We determine the influence of substitutional defects on perovskite quantum dots through experimental and theoretical investigations. Substitutional defects were introduced by trivalent dopants (In, Sb, and Bi) in CsPbBr₃ by ligand-assisted reprecipitation. We show that the photoluminescence (PL) emission peak shifts toward shorter wavelengths when doping concentrations are increased. Trivalent metal-doped CsPbBr₃ enhanced the PL quantum yield (~10%) and air stability (over 10 days). Our findings provide new insights into the influence of substitutional defects on substituted CsPbBr₃ that underpin their physical properties.

An electrical and optical responsive chemical‐semiconductor gas sensor is developed using Cu(I) halides with a phase transition mechanism. Cu(I) materials exhibit reversible phase transitions between the Cs₃Cu₂I₅ and CsCu₂I₃ with different properties, owing to the formation/destruction of the Cs–I and Cu–Cu bonding when the hydroxyl groups are attached/detached. Among various toxic and atmospheric gases, a Cu(I)‐based gas sensor has high selectivity in detecting the hydroxyl group, and the highest sensitivity to water. The reactivity is determined by the polarity, where water with the largest polarity has the strongest attraction for Cu⁺ and I⁻ ions, letting phase transition occur easily. The multimodal sensor red‐shifts emission from 445 to 575 nm when it detects hydroxyl gas, and the moisture‐sensitive sensor visually confirms response to breaths in less than 5 s and recovery in the air in less than 30 s. The gas sensor can operate at room temperature while applying a constant bias voltage of 1 V, and it also shows excellent sensitivity in a relative humidity range of 15–75%. Furthermore, the sensor maintained ≈90% of its initial responsivity over 1 year.

The photo-physical properties of halide perovskite films, photoluminescence intensity, and emission peak are controlled through solvent vapour annealing.

High contrast and reversible luminescence thermochromism behavior of the Cs ₄ PbBr ₆ perovskite in the solid state is demonstrated and its origin is systemically investigated.