Interface energetics and dynamics in organic-inorganic hybrid perovskites

• Main Author: Goh, Teck Wee
• Other Authors: Sum Tze Chien
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: DRNTU::Science::Physics::Descriptive and experimental mechanics; DRNTU::Engineering::Materials::Compositional materials science
• Online Access: https://hdl.handle.net/10356/84081; http://hdl.handle.net/10220/48558
• Institution: Nanyang Technological University

Organic-inorganic lead halide perovskites have gained a lot of attention over the past six years as a desirable class of materials for various devices which has been shown to possess desirable properties such as long diffusion lengths, large carrier mobility, low trap states. At present, some important topics in this research have not been adequately addressed, like interface energetics, hot carrier dynamics and problems with UV degradation. This thesis is dedicated to address these issues. Firstly, the interface energetics of FAPbI3-based perovskites with organic charge extraction layers showed apparent upward band bending, but its origin is unexpectedly due to presence of δ-FAPbI3. This finding implicates solar cell operation as it causes inefficient extraction of photoexcited electrons to the PCBM. In the second part of the work, a successful homemade TR-2PPE system was set up, and preliminary studies on CsPbBr3 single crystals found that hot carriers generated through carrier-carrier scattering ∼1 eV above the conduction band edge possess long lifetimes ∼3 ns under resonant excitation due to strong band-filling and long lifetimes of band edge carriers in single crystals which hinder hot carrier cooling. This observation in CsPbBr3 may point towards using perovskite single crystals to generate and extract hot carriers in solar cells. The last part of this work addresses the issue of UV instability of perovskites in MAPbI3 through the addition of Hindered Amine Light Stabilisers (HALS) to suppress photodegradation by UV light through photo-oxidation and free radical formation of perovskite. A systematic study was performed by doping MAPbI3 through antisolvent treatment with four representative HALS compounds with varying functional groups and molecular sizes to study their effects on film formation, morphology and resulting photostability enhancement under UV light. Surprisingly, doping with different HALS compounds provides varying photostability enhancements and may even result in more photodegradation in some cases due to the influence of functional group and size on surface morphology, crystallinity and surface coverage. Among the HALS compounds, the polymeric one gave the best photostability enhancement with reduction of photodegradation by 59.2%. This method would not only be potentially useful for solar cell applications, but also in optical spectroscopy that uses UV light like TR-2PPE.