Shufang Zhang

Amorphous ZnO based resistive random access memory

Amorphous zinc oxide (a-ZnO) based resistive random access memory (RRAM) Ag/a-ZnO/Pt devices were fabricated and their resistive switching characteristics investigated. The Ag/a-ZnO/Pt RRAMs exhibit typical bipolar resistive switching features with the resistance ratio of high to low resistance states (HRS/LRS) more than 107. Detailed current–voltage I–V characteristic analysis suggests that the conduction mechanism in the low resistance state is due to the formation of metallic filaments. Schottky emission is proven to be the dominant conduction mechanism in the high resistance state which results from the Schottky contacts between the metal electrodes and ZnO. The Ag/a-ZnO/Pt devices also show excellent retention performance. These results suggest promising application potentials for Ag/a-ZnO/Pt RRAMs.

Air-stable CsPb1−xBixBr3 (0 ≤ x ≪ 1) perovskite crystals: optoelectronic and photostriction properties

The growth of single crystals allows a more accurate and reliable study of the intrinsic electrical and optical properties of halide perovskite materials. However, all-inorganic halide perovskite single crystals are difficult to prepare due to the poor solubility of the reactant precursors. In this paper, we report a series of air-stable Cs-based halide perovskite single crystals, CsPbBr3 and CsPb1−xBixBr3 (x ≪ 1), prepared via a modified antisolvent vapour-assisted crystallization method. The Cs-based halide perovskites exhibited low trap density and high carrier mobility that are comparable to those of organic–inorganic hybrid halide perovskite materials. Most importantly, the Bi-doped CsPb1−xBixBr3 perovskites also indicated excellent light absorption (covering the entire visible wavelength) and photostriction (effective photostriction of about 8 × 10−4) performances, which greatly expands the optoelectronic and optomechanical applications of these inorganic halide perovskite materials.

CuO/ZnO memristors via oxygen or metal migration controlled by electrodes

We carry out a comparative study on resistive switching in CuO/ZnO bilayer films; both samples grown Pt and Ag electrodes show bipolar switching behaviors. The two kinds of current-voltage curves reveal the different resistive switching behaviors in Pt/CuO/ZnO/Pt and Ag/CuO/ZnO/Pt, respectively. We conjecture that the formation and rupture of conducting filaments are responsible for the switching effect. Filaments induced by migration of oxygen ions are responsible for resistive switching with the Pt electrode. In contrast, resistive switching with the Ag electrode is attributed to the migration of metal cations and the corresponding electrochemical metallization. It is also inferred that the characteristic nature of the conducting filaments influences many aspects of switching characteristics, including the switching voltages and cycling variations at room temperature.

Enhancing moisture-tolerance and photovoltaic performances of FAPbI3 by bismuth incorporation

The power conversion efficiency (PCE) of perovskite-based solar cells has already exceeded of 22% due to their unique optoelectronic properties. However, the long-term ambient air stability as the Achilles heel of such promising photovoltaic materials has to be solved for commercialization. Herein, a facile method that partially substitutes B-site Pb2+ by Bi3+ was suggested to enhance moisture tolerance and photovoltaic performances for FAPbI3. The partial incorporation of Bi in FAPbI3 tuned a more favourable tolerance factor and suppressed the phase transition from black perovskite phase to yellow non-perovskite phase at room temperature. The solar cells based on the incorporation of 5 mol% Bi3+ compounds achieved a substantially improved PCE of 17.78%, which is much higher than that of the controlled device with pure FAPbI3 (13.02%). Moreover, the optimal solar cell showed remarkable stability, maintaining 62.38% of the initial PCE without encapsulation for 1000 h under ambient conditions at 25 °C with relative humidity of 30%. This work further demonstrated the possibility of substituting Pb2+ by non-equivalent elements, thus opening the door for further developments of such promising materials.

Recent Advances in One-Dimensional Halide Perovskites for Optoelectronic Applications

Metal-halide perovskites have emerged as efficient, low-cost energy materials owing to their remarkable optoelectronic properties. In particular, the dimensionality and morphology of crystallites may have a striking influence on their chemical and physical properties and therefore affect their optoelectronic applications. One-dimensional halide perovskites have superior carrier transportation in one dimension, high crystalline quality, and consequently, high quantum efficiencies and long carrier diffusion lengths, which are important for the performance of perovskite-based nanoscale optoelectronic and photonic devices. In this review, we highlight recent advances in the synthesis of one-dimensional halide perovskites and their unique properties as well as their novel optoelectronic applications. This review aims to provide an overview of the achievements in synthesis techniques and nanoscale optoelectronic applications based on one-dimensional perovskite nanocrystals.

Improved performance and stability of perovskite solar cells by incorporating gamma-aminobutyric acid in CH3NH3PbI3

Organic–inorganic hybrid perovskites have attracted enormous attention due to their remarkable properties for high-efficiency solar cells in recent years. However, controlling the morphology of perovskite films is still a challenge using a solution synthesis method. Perovskite films with incomplete coverage are inevitable and this significantly limits the device photoelectric performance and long-term stability. In this work, we have combined gamma-aminobutyric acid iodide (GABAI) and CH3NH3I (MAI) as a mixed amine source in a precursor solution to fabricate a mixed-cation perovskite (GABA)xMA1−xPbI3. As a result, high quality (GABA)xMA1−xPbI3 crystals were synthesized and showed better pore-filling and more complete contact with the TiO2 scaffold, enhancing the power conversion efficiency from 15.08 to 18.31% with respect to the controlled MAPbI3 solar cells. Importantly, the devices that contained GABA+ also showed much higher stability when compared to the reference MAPbI3 devices. This new chemical modification design, using bifunctional mixed cations in organic–inorganic hybrid perovskites, provides an efficient approach for improving both the performance and stability simultaneously.

Highly efficient flexible solar cells based on a room-temperature processed inorganic perovskite

All-inorganic perovskite cesium lead triiodine (CsPbI3) is emerging as a promising thermally stable light absorber in flexible optoelectronic devices. However, the photoactive α-CsPbI3 only exists at a temperature higher than 310 °C and rapidly degrades to the undesired δ-CsPbI3 at room temperature. Here, a vacuum-assisted drying process is first developed to fabricate all-inorganic perovskite thin films at room temperature. The film morphology and photoelectric properties as well as the long-time stability are significantly improved compared to those of the reference film fabricated with annealing process. The flexible solar cells based on such room temperature processed films demonstrate a high power conversion efficiency of 11.47% with a small hysteresis. Moreover, the champion flexible cell also exhibits high air-stability and excellent flexibility. These results offer a new pathway for developing high-performance and cost-effective flexible optoelectronic devices.