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Improving Metal Halide Perovskite Crystal Quality from Surface to Interior for Photovoltaic Device
Metal halide perovskites (MHPs) as the most promising semiconductor material for photovoltaic devices, has boosted the power conversion efficiency to 25.2% for solar cells and 29.1% for perovskite/Si tandem solar cells in merely several years development. In this dissertation, we focus on the performance and stability enhancement for low-cost solution-processed metal halide perovskite photovoltaic devices by reducing trap density and improving quality of the crystals (grains) from surface to interior. In Chapter 2, we observed the existence of nanocrystals and some amorphous phases at the surface of apparent single crystalline grains in solution-processed polycrystalline films which is the origin of the accelerated degradation of MHPs. By removing the defective surface layer through mechanical polishing, the stability of perovskite films is significantly enhanced. Encapsulated solar cells based on polished MHPs retain 93% of its initial efficiency after continuous illumination for 2180 hours at 1 sun intensity and with ultraviolet at 65 °C. This study narrows down the stability gap between the MHP polycrystalline films and single crystal perovskites which represents the upper limit for the stability of MHPs. In Chapter 3, I developed a chemical slurry designed for metal halide perovskite for the first time to apply the typical chemical mechanical polishing (CMP) technique. We obtained the ultra-smooth “mirror-like” single crystal surface in nanoscale of roughness (Rms of 5.3 nm) without introducing damage or scratch. In Chapter 4, adding sulfonic zwitterion molecular in precursor and obtained the high quality of MAPbI3 single crystal grown by inverse temperature crystallization (ITC) method as the state of the art. The crystallinity has been increased significantly to be the record, and the defect density has been reduced 50 times, the ion migration under bias has been largely suppressed.
Engineering|Materials science|Nanoscience|Chemical engineering|Particle physics|Energy
Liu, Ye, "Improving Metal Halide Perovskite Crystal Quality from Surface to Interior for Photovoltaic Device" (2020). ETD collection for University of Nebraska - Lincoln. AAI28088904.