Nanocrystal optoelectronic devices : from materials synthesis to structural engineering

Abstract

Semiconducting nanomaterials hold great promise for the advancement of optoelectronic applications in the next generation. This thesis focuses on two specific types of nanocrystals: silver bismuth sulfide (AgBiS₂) and inorganic halide perovskite (CsPbX₃). Our research involves integrating these nanocrystals into solar cell and light emitting devices, with a focus on characterizing their performance. In the AgBiS₂ project, we explore two different solar cell structures: n-i-p and p-i-n. Our findings indicate that the p-i-n structure shows greater promise for AgBiS₂, as the NiO/AgBiS₂ heterojunction enables more efficient charge transport, resulting in higher efficiency. Additionally, we incorporate a singlet fission chromophore, pentacene, to form an AgBiS₂/Pc heterojunction. Through transient spectroscopy, we observe efficient charge harvesting between AgBiS₂ and pentacene, leading to the development of the first singlet-fission solar cell based on AgBiS₂ material. In the CsPbX₃ project, we initially investigate anion exchange in CsPbBr₃ nanocrystals synthesized at room temperature. By switching the anion from chloride to iodide, we achieve color emission covering the entire visible spectrum. To protect the nanocrystals during the anion exchange, we employ a post-treatment strategy that enhances the quantum yield. Furthermore, we fabricate pure-red CsPbI₃ quantum dot LEDs by leveraging the quantum confinement effect. Through a moderate ligand exchange process, we replace long-chain ligands with short-chain amino-acid ligands, resulting in improved efficiency and lifetime of the LED devices. Both studies provide valuable insights into the potential enhancements of nanocrystal optoelectronic devices.

Date of Award	2023
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Jonathan Eugene HALPERT (Supervisor) & Kam Sing WONG (Supervisor)