van der Waals Metal Contacts for Characterization and Optoelectronic Application of Metal Halide Perovskite Thin Films

The metal contacts on metal halide perovskite thin films are often formed through physical vapor deposition (PVD) processes for investigation of the film properties or construction of optoelectronic devices. However, the PVD processes generate high-energy metal atoms, directly bombarding the film surface, potentially causing unintended damage in the film. In this study, we performed systematic investigation on the impact of a PVD-processed metal contact on the optoelectronic properties of underlying organic–inorganic hybrid perovskite thin films. We adopted a physically laminated van der Waals metal contact for comparison to enable quantitative analysis. Through space-charge-limited current measurement, we demonstrated the defect density increases by 26–48% on average after formation of the metal contact by the PVD process. In-situ photoluminescence measurements unraveled that the generated defects easily migrate under the electric field to seriously deteriorate the performance and stability of photodetectors. This study highlights the importance of the intact junction between the perovskite and metal contacts for characterization and optoelectronic application of perovskite thin films

van der Waals Metal Contacts for Characterization and Optoelectronic Application of Metal Halide Perovskite Thin Films

The metal contacts on metal halide perovskite thin films are often formed through physical vapor deposition (PVD) processes for investigation of the film properties or construction of optoelectronic devices. However, the PVD processes generate high-energy metal atoms, directly bombarding the film surface, potentially causing unintended damage in the film. In this study, we performed systematic investigation on the impact of a PVD-processed metal contact on the optoelectronic properties of underlying organic–inorganic hybrid perovskite thin films. We adopted a physically laminated van der Waals metal contact for comparison to enable quantitative analysis. Through space-charge-limited current measurement, we demonstrated the defect density increases by 26–48% on average after formation of the metal contact by the PVD process. In-situ photoluminescence measurements unraveled that the generated defects easily migrate under the electric field to seriously deteriorate the performance and stability of photodetectors. This study highlights the importance of the intact junction between the perovskite and metal contacts for characterization and optoelectronic application of perovskite thin films

Artificial Synapse Based on a δ‑FAPbI₃/Atomic-Layer-Deposited SnO₂ Bilayer Memristor

Halide perovskite-based resistive switching memory (memristor) has potential in an artificial synapse. However, an abrupt switch behavior observed for a formamidinium lead triiodide (FAPbI3)-based memristor is undesirable for an artificial synapse. Here, we report on the δ-FAPbI3/atomic-layer-deposited (ALD)-SnO2 bilayer memristor for gradual analogue resistive switching. In comparison to a single-layer δ-FAPbI3 memristor, the heterojunction δ-FAPbI3/ALD-SnO2 bilayer effectively reduces the current level in the high-resistance state. The analog resistive switching characteristics of δ-FAPbI3/ALD-SnO2 demonstrate exceptional linearity and potentiation/depression performance, resembling an artificial synapse for neuromorphic computing. The nonlinearity of long-term potentiation and long-term depression is notably decreased from 12.26 to 0.60 and from −8.79 to −3.47, respectively. Moreover, the δ-FAPbI3/ALD-SnO2 bilayer achieves a recognition rate of ≤94.04% based on the modified National Institute of Standards and Technology database (MNIST), establishing its potential in an efficient artificial synapse

Enhancing Efficiency and Stability of Tin Halide Perovskite Light-Emitting Diodes via Engineered Alkali/Multivalent Metal Salts

Sn-based perovskite light-emitting diodes (PeLEDs) have emerged as promising alternatives to Pb-based PeLEDs with their rapid increase in performance owing to the various research studies on inhibiting Sn oxidation. However, the absence of defect passivation strategies for Sn-based perovskite LEDs necessitates further research in this field. We performed systematic studies to investigate the design rules for defect passivation agents for Sn-based perovskites by incorporating alkali/multivalent metal salts with various cations and anions. From the computational and experimental analyses, sodium trifluoromethanesulfonate (NaTFMS) was found to be the most effective passivation agent for PEA2SnI4 films among the explored candidate agents owing to favorable reaction energetics to passivate iodide Frenkel defects. Consequently, the incorporation of NaTFMS facilitates the formation of uniform films with relatively large crystals and reduced Sn4+. The NaTFMS-containing PEA2SnI4 PeLEDs demonstrate an improved luminance of 138.9 cd/m2 and external quantum efficiency (EQE) of 0.39% with an improved half-lifetime of more than threefold. This work provides important insight into the design of defect passivation agents for Sn-based perovskites

Composition-Dependent Optoelectronic Properties of Mixed 2D/3D Metal Halide Perovskite Films for Light-Emitting Diodes

Low-dimensional perovskites with large organic cations have shown great potential for boosting the luminescence efficiency of metal halide perovskite light-emitting diodes (PeLEDs). Although numerous successful results have been obtained for mixed two-dimensional (2D)/three-dimensional (3D) perovskite films, the correlation of the optoelectronic properties with the crystallographic properties and film composition remains elusive. Herein, we investigated the optoelectronic quality of thin films and their impact on luminescence and transport behaviors in a mixed 2D/3D perovskite system containing 2D butylammonium lead bromide (BA2PbBr4) and 3D formamidinium lead bromide (FAPbBr3). Ultrafast transient absorption and temperature-dependent photoluminescence measurements revealed distinct changes in nonemissive decay of the excited states, including the vibrational coupling properties. These behaviors could then be closely correlated with the crystallographic evolution of the perovskite films. We rationalized the performance of PeLED devices and determined the possible limitations to further utilize the advantageous properties of mixed 2D/3D perovskite systems by examining both the luminescence and electrical properties of the perovskite films