Characterisation of Single CsPbBr3 Perovskite Nanowire Devices with Ag Electrodes

Abstract

Metal halide perovskites are widely researched for their optoelectronic properties and potential applications. They are made into devices by being contacted with different electrode materials. In particular, perovskite devices with silver (Ag) electrodes have been studied for their potential applications as memristors, taking advantage of Ag ion migration which can be controlled by the polarity of an applied electric field. The devices studied in this thesis work are single nanowires made of the perovskite caesium lead bromide (CsPbBr3). Some of these devices are contacted with one Ag and one titanium/gold (Ti/Au) electrode (the Ag|CsPbBr3|(Ti/Au) configuration), while others have two Ag electrodes (Ag|CsPbBr3|Ag). The already-fabricated devices were characterised electrically under dark conditions as well as by using electron spectroscopy techniques including scanning electron microscopy and energy dispersive X-ray spectroscopy (EDS). The devices were also checked for any photoluminescence (PL) response. The I–V curves showed very low currents in general, and rather drastic changes in device morphology were observed due to the external electric field. It was confirmed with EDS that there was considerable Ag migration that led to the formation of Ag structures on the surface of the nanowires, which was irreversible under an electric field of the opposite polarity. Moreover, the lack of PL suggested altered perovskite lattice. Additional techniques such as X-ray photoelectron spectroscopy and X-ray diffraction are needed to investigate the chemical state of the present Ag and any change in the bulk properties of the nanowires, respectively.

Popular Abstract

Can we make resistors remember information?

Semiconductors make up key components in our beloved daily electronics, for which a large data storage capacity is desirable. In this project, we explore beyond traditional semiconductor materials for memory applications in electronics.

A memristor (short for memory-resistor) is an electronic device that can switch between states with different resistance depending on the direction of current flow, which is controlled by an applied electric bias. The “SET” process occurs when a high bias of one polarity is applied, putting the memristor in its low resistance state (“ON” state); when the opposite bias is applied during the “RESET” process, the memristor switches to its high resistance state (“OFF” state). The memory property is seen when the applied electric field is removed – the memristor can remember its resistance. This property can be important in data storage applications based on resistive-switching memory devices.

The term perovskite is the mineral name of calcium titanate (CaTiO3), named after the mineralogist Lev Perovski. Since CaTiO3 has a special crystal structure, the term perovskite is also commonly used to refer to all ionic compounds that have this crystal structure. Many interesting properties come with this crystal structure. For one, they can produce notably higher current under illumination than in the dark. Also, depending on the exact composition, perovskites can emit light of a wide range of colours when illuminated. Additionally, due to the ionic nature of perovskites, it is relatively easy for impurity ions to move through the lattice. This property of perovskites is utilised to make memristor devices – ion movements driven by an electric field control whether they are turned “ON” or “OFF”.

Nanowires are structures that have a diameter of at most a few hundred nanometers (1 nanometer is 0.0000001 times of 1 centimeter), and they are typically a couple of micrometers long (1 micrometer is 0.0001 times of 1 centimeter). These extremely tiny structures are much longer than they are wide. This means that whenever nanowires are integrated into an electronic device, current basically flows in one direction. Nanowires are ideal to be incorporated into chips, which are becoming smaller and smaller nowadays. Furthermore, their open geometry allows us to inspect their conditions directly.

The attractive properties of perovskites and the nanowire geometry prompt us to study single perovskite nanowires sandwiched between two metal electrodes. More specifically, the perovskite studied in this project is caesium lead bromide (CsPbBr3), and the two electrode material combinations are silver/gold and silver/silver. Unexpectedly, these devices did not show memory behaviour: there was no clear distinction between high and low resistance states, and silver movements destroyed the perovskite crystal. To better understand the underlying cause of this outcome, additional techniques are needed.

• author: Fang, Cecilia
• supervisor: Jesper Wallentin; Ziyun Huang
• organization: Synchrotron Radiation Research; Department of Physics
• alternative title: Characterisation of Single Caesium Lead Bromide Perovskite Nanowire Devices with Silver Electrodes
• course: FYSK04 20251
• year: 2025
• type: M2 - Bachelor Degree
• subject: Physics and Astronomy
• keywords: semiconductor, perovskite, memristor
• language: English
• id: 9190453
• date added to LUP: 2025-06-02 14:01:47
• date last changed: 2025-06-02 14:01:47