Aluminum-Doped Zinc Oxide as Highly Stable Electron Collection Layer for Perovskite Solar Cells

Although low-temperature, solution-processed zinc oxide (ZnO) has been widely adopted as the electron collection layer (ECL) in perovskite solar cells (PSCs) because of its simple synthesis and excellent electrical properties such as high charge mobility, the thermal stability of the perovskite films deposited atop ZnO layer remains as a major issue. Herein, we addressed this problem by employing aluminum-doped zinc oxide (AZO) as the ECL and obtained extraordinarily thermally stable perovskite layers. The improvement of the thermal stability was ascribed to diminish of the Lewis acid–base chemical reaction between perovskite and ECL. Notably, the outstanding transmittance and conductivity also render AZO layer as an ideal candidate for transparent conductive electrodes, which enables a simplified cell structure featuring glass/AZO/perovskite/Spiro-OMeTAD/Au. Optimization of the perovskite layer leads to an excellent and repeatable photovoltaic performance, with the champion cell exhibiting an open-circuit voltage (<i>V</i>_oc) of 0.94 V, a short-circuit current (<i>J</i>_sc) of 20.2 mA cm^–2, a fill factor (FF) of 0.67, and an overall power conversion efficiency (PCE) of 12.6% under standard 1 sun illumination. It was also revealed by steady-state and time-resolved photoluminescence that the AZO/perovskite interface resulted in less quenching than that between perovskite and hole transport material

Competition between Metallic and Vacancy Defect Conductive Filaments in a CH₃NH₃PbI₃‑Based Memory Device

Ion migration, which can be classified into cation migration and anion migration, is at the heart of redox-based resistive random access memory. However, the coexistence of these two types of ion migration and the resultant conductive filaments (CFs) have not been experimentally demonstrated in a single memory cell. Here we investigate the competition between metallic and vacancy defect CFs in a Ag/CH₃NH₃PbI₃/Pt structure, where Ag and CH₃NH₃PbI₃ serve as the top electrode and memory medium, respectively. When the medium layer thickness is hundreds of nanometers, the formation/diffusion of iodine vacancy (V_I) CFs dominates the resistive switching behaviors. The V_I-based CFs provide a unique opportunity for the electrical-write and optical-erase operation in a memory cell. The Ag CFs emerge and coexist with V_I ones as the medium layer thickness is reduced to ∼90 nm. Our work not only enriches the mechanisms of the resistive switching but also would advance the multifunctionalization of resistive random access memory

Laser-Induced Flash-Evaporation Printing CH₃NH₃PbI₃ Thin Films for High-Performance Planar Solar Cells

Organic–inorganic hybrid perovskites have been emerging as promising light-harvesting materials for high-efficiency solar cells recently. Compared to solution-based methods, vapor-based deposition technologies are more suitable in preparing compact, uniform, and large-scale perovskite thin films. Here, we utilized flash-evaporation printing (FEP), a laser-induced ultrafast single source evaporation method employing a carbon nanotube evaporator, to fabricate high-quality methylammonium lead iodide perovskite thin films. Stoichiometric films with pure tetragonal perovskite phase can be achieved using a controlled methylammonium iodide to lead iodide ratio in evaporation precursors. The film crystallinity and crystal grain growth could further be promoted after postannealing. Planar solar cells (0.06 cm²) employing these perovskite films exhibit a champion power conversion efficiency (PCE) of 16.8% with insignificant hysteresis, which is among the highest reported PCEs using vapor-based deposition methods. Large-area (1 cm²) devices based on such perovskite films also achieved a stabilized PCE of 11.2%, indicating the feasibility and scalability of our FEP method in fabricating large-area perovskite films for other optoelectronic applications