Abstract
The practical application of metal halide perovskites in optoelectronic devices is currently mainly limited by their instability under environmental stress, such as common environmental factors such as humidity, oxygen, and high temperature, which can affect material properties. This thesis focuses on this core issue and advances it through two interrelated directions: additive engineering and degradation mechanism research, covering both three-dimensional (3D) and two-dimensional (2D) perovskite systems.
In the research on 3D systems, a strategy to enhance the stability of methylamine free perovskite solar cells (PSCs) was proposed. Specifically, 2- (2-naphthyl) ethylamine hydrochloride (22n) is introduced as a functional additive into the perovskite precursor. From the perspective of material properties, 22n has unique reducing properties, which can effectively suppress the oxidation of iodide in the precursor solution, while also passivating defects in the final formed perovskite film. This treatment not only improves the quality and uniformity of the perovskite layer, but also enhances its resistance to degradation caused by moisture. From experiment, the addition of optimized concentration 22n PSCs not only achieved a champion power conversion efficiency (PCE) of 23.2%, but more importantly, after continuous operation for 300 hours in high humidity environments, it still retained 93% of the initial PCE - a performance significantly better than the control group devices (only retaining 82%).
On the basis of stability studies, another work focuses on the degradation mechanism of 2D Ruddlesden Popper perovskites, with particular attention to the significant stability differences between lead based and tin based analogues - a key issue that has not been fully clarified in previous research. A comparative study on A2PbI4 and A2SnI4 (where A is 2-thiophenethylamine (TEA) and 4-fluorophenylethylamine (FPEA)) was conducted, and essential differences in the degradation pathways of the two types of materials were founded. Unlike lead based materials, A2SnI4 films that have undergone aging produce amorphous SnO2, and there is no release of ammonia gas (NH3) during the process, which also confirms the key differences in the redox chemical reactions in the two types of materials. Based on the understanding of these mechanisms, additives for improving the stability of TEA2SnI4 were investigated.
Overall, the research in this thesis provides a comprehensive contribution to the field: not only have effective additive based strategies been developed for 3D lead based and 2D tin based perovskites to enhance their stability, but also provide a clear guidance by elucidating the intrinsic mechanisms of material degradation.
Anyone interested is welcome to attend.