Engineered Surface Halide Defects by Two-Dimensional Perovskite Passivation for Deformable Intelligent Photodetectors

Modulating Dimensionality of 2D Perovskite Layers for Efficient and Stable 2D/3D Perovskite Photodetectors

Two-dimensional (2D) perovskites have been widely adopted for improving the performance and stability of three-dimensional (3D) metal halide perovskite devices. However, rational manipulation of the phase composition of 2D perovskites for suitable energy level alignment in 2D/3D perovskite photodetectors (PDs) has been rarely explored. Herein, we precisely controlled the dimensionality of the 2D perovskite on CsPbI2Br films by tuning the polarity of the n-butylammonium iodide (BAI)-based solvents. In comparison to the pure n = 1 2D perovskite (ACN-BAI) formed by acetonitrile treatment, a mixture of n = 1 and n = 2 phases (IPA-BAI) generated by isopropanol (IPA) treatment guaranteed more robust defect passivation and favorable energy level alignment at the perovskite/hole transport layer interface. Consequently, the IPA-BAI PD exhibited a responsivity of 0.41 A W-1, a detectivity of 1.01 × 1013 Jones, and a linear dynamic range of 120 dB. Furthermore, the mixed-phase 2D layer effectively shielded the 3D perovskite from moisture. The IPA-BAI device retained 76% of its initial responsivity after 500 h of nonencapsulated storage at 10% relative humidity. This research provides valuable insights into the dimensional modulation of 2D perovskites for further enhancing the performance of 2D/3D perovskite PDs.

Recent advance of high-quality perovskite nanostructure and its application in flexible photodetectors

Flexible photodetectors (PDs) have garnered increasing attention for their potential applications in diverse fields, including weather monitoring, smart robotics, smart textiles, electronic eyes, wearable biomedical monitoring devices, and so on. Notably, perovskite nanostructures have emerged as a promising material for flexible PDs due to their distinctive features, such as a large optical absorption coefficient, tunable band gap, extended photoluminescence decay time, high carrier mobility, low defect density, long exciton diffusion lengths, strong self-trapped effect, good mechanical flexibility, and facile synthesis methods. In this review, we first introduce various synthesis methods for perovskite nanostructures and elucidate their corresponding optical and electrical properties, encompassing quantum dots, nanocrystals, nanowires, nanobelts, nanosheets, single-crystal thin films, polycrystalline thin films, and nanostructured arrays. Furthermore, the working mechanism and key performance parameters of optoelectronic devices are summarized. The review also systematically compiles recent advancements in flexible PDs based on various nanostructured perovskites. Finally, we present the current challenges and prospects for the development of perovskite nanostructures-based flexible PDs.

Fluorination and Conjugation Engineering Synergistically Enhance the Optoelectronic Properties of Two-Dimensional Hybrid Organic-Inorganic Perovskites

Two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs) are expected to be a viable alternative to three-dimensional (3D) analogs in solar cells (SCs) and optoelectronic devices due to their high stability, diverse composition, and physical properties. However, unsuitable band alignment and large bandgaps limit the power conversion efficiency (PCE) improvement of SCs based on 2D HOIPs. Here, we report a molecular design strategy that combines fluorination and conjugation engineering to tune the electronic structure and optimize the PCE of 2D HOIPs. Our results show that type IIa band alignment and tunable bandgaps can be achieved in 2D Dion-Jacobson (DJ) HOIPs by H/F substitution of organic cations with different degrees of conjugation. In general, the bandgap of 2D DJ-HOIPs decreases monotonously with the increase of the number of F atoms, which is due to the gradual decrease of the lowest unoccupied molecular orbitals (LUMO) of organic cations. In addition, the enhanced interlayer charge transfer and higher dielectric constant suggest that the fluorination-induced dielectric limitations are weakened. The estimated PCE of 2D DJ-HOIPs is exponentially increased and positively correlated with the degree of conjugation and fluorination of organic cations, with a PCE approaching 29% under their synergistic effect. Our results not only provide promising candidates for photovoltaic device applications but also provide an effective method for PCE optimization.

Metal-Free PAZE-NH4 X3 ⋅H2 O Perovskite for Flexible Transparent X-ray Detection and Imaging

Metal-free perovskites are of interest for their chemical diversity and eco-friendly properties, and recently have been used for X-ray detection with superior carrier behavior. However, the size and shape complexity of the organic components results in difficulties in evaluating their stability in high-energy radiation. Herein, we introduce multiple hydrogen-bond metal-free PAZE-NH₄ X₃ ⋅H₂ O perovskite, where H₂ O leads to more hydrogen bonds appearing between organic molecules and the perovskite host. As suggested by the theoretical calculations, multiple hydrogen bonds promote stiffness of the lattice, and increase the diffusion barrier to inhibit ionic migration. Then, low trap density, high μτ products and structural flexibility of PAZE-NH₄ Br₃ ⋅H₂ O give a flexible X-ray detector with the highest sensitivity of 3708 μC Gy_air ^-1  cm^-2 , ultra-low detection limit of 0.19 μGy_air ^-1  s^-1 and superior spatial resolution of 5.0 lp mm^-1 .