Materials chemistry and device design : improving the functionality of perovskite optoelectronic devices

Abstract

Perovskite materials have sparked great excitement in optoelectronics in last two decades due to their low-cost and high-performance in devices. The devices include solar cells (SCs), light-emitting diodes (LEDs), photodetectors, X‐ ray detectors, lasers and memristors. Generally, perovskite structures can be synthesized in a variety of forms such as bulk material, two-dimensional materials, and colloidal quantum dots (QDs). Bulk perovskite materials have shown tremendous progress in SCs, achieving remarkable power conversion efficiencies (PCEs). On the other side, perovskite QDs have become the new paradigm for LEDs due to their high photoluminescence quantum yield (PLQY) and tunable emission wavelength. By employing perovskites as an active layer of the LED or SCs, high-performance functional devices can be fabricated. This is due to their unique features such as ease of synthesis, size control, and composition tunability of the bandgap and confined excitons. In this research, we investigate perovskite synthesis, solvent chemistry, and its impact on device performances. The research is divided into three parts. At first, we focus on the perovskite QDs synthesis, optoelectronic properties, their application in SCs. The current state of the art of QDs, problems associated with ligand chemistry, is briefly investigated. Perovskite QD devices still deteriorate from fabrication issues such as poor surface morphology, surface defects, and notably insulating native lands such as anionic oleate and cationic oleylammonium ligands. A novel layer-by-layer (LBL) ligand chemistry has been developed to overcome the problems. As a result, QDSC was fabricated in p–i–n inverted configurations. The efficiency was improved from 11.50 % for the control to 13.1 % for the new ligand chemistry devices. In the second part, solvent engineering of formamidinium lead bromide (FAPbBr₃) perovskites have been investigated. The one-step fabrication of FAPbBr₃ perovskites has not been thoroughly investigated. Particularly, solvent‐dependent crystallization, the chemical transformation route to FAPbBr₃, and the crystalline intermediates of FA‐based perovskites. Herein, a new protocol using a one‐step deposition method for producing formamidinium lead bromide (FAPbBr₃) perovskites are reported, which features a solvent‐engineered intermediate phase to achieve superior films. As a result, inverted SCs using solvent engineered films achieve power conversion efficiencies (PCEs) of up to 9.06 %, the highest reported efficiency for inverted FAPbBr₃ perovskite devices. The third part focuses on fabricating semitransparent perovskite SCs (STPSCs) based on FAPbBr₃ perovskites. We varied the perovskite precursors concentrations and optimized the antisolvent strategy to achieve high-quality pin-hole free films. The semitransparent devices with different concentrations such as C1 (1.2 M), C2 (0.8 M), C3 (0.4 M) obtained the average visible transmittance of 35.6 %, 42.5 % and 49.2 %, respectively. The device results are presented with future directions. The last project is carried out to find the solution for the stability of iodide-based perovskite. We have identified the polymer PCF, which improves the stability and photoluminescence of MAPbI₃ perovskites. The passivation of defects using PCF has been thoroughly investigated. The PCF structural properties and crystallization effects on MAPbI₃ grains have been studied. Near-infrared LED has been constructed based on utilizing an optimized concentration of PCF polymer. Collectively, this research includes the synthesis of inorganic MHPs nanostructures, ligand chemistry for efficient devices, solvent engineering in wideband gap FAPbBr₃ perovskites. The projects utilized various in-depth scientific characterizations on pursuing the fundamental understanding of the synthesis, material properties and fabrication of efficient devices.

Date of Award	2021
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Jonathan Eugene HALPERT (Supervisor)