UCLA

Organic and perovskite materials have shown a remarkable promise for solar cell manufacturing due to scalability, low cost and flexibility of the material compared to other solar panel technologies. The major challenge for organic and perovskite solar cell commercialization, however, is whether they can perform and last as long as silicon panels, which often depends on the molecular properties of materials. Hence, this dissertation focuses on understanding the crucial role and the effect that small molecules have on the efficiency and stability of organic and perovskite solar cells. Chapter 1 explores the inter- and intramolecular interactions of small molecules in organic solar cells. The electron-withdrawing character of functional groups and extension of conjugation strongly contributed to the performance of organic solar cells. Chapter 2 dives into radical formation in a novel small molecule hole-transport material for perovskite photovoltaics and its role in performance and stability of the device. In Chapter 3 and 4, recently designed spirofluorene-based π∙∙∙π-bonded organic framework and a spiroconjugated small molecule are introduced, both of which present remarkable transport properties in organic electronics. Chapter 5 and 6 examine the interactions between small molecules and perovskite quantum dots (QDs). First, a process that controls the density of small molecules on QD surface is developed, after which a small molecule is integrated onto the surface of QDs resulting in improved device performance. The focus then advances to the analysis of small molecule interactions with the thin-film perovskite. Chapter 7 demonstrates a kinetically-controlled and substrate-tolerant local epitaxial growth of formamidinium-based perovskite for thin-films using a cheap, versatile and simple method that improved stability and performance. Chapter 8 and 9 delve into passivation of perovskite defects using small molecules. Theophylline, a small molecule found in tea, emerged to be a strong candidate for silencing the most probable defects on perovskite surface due to its optimal configuration relative to the surface. It was also discovered that the passivation of perovskite surface defects with two small molecules can have synergistic effect on enhancing the performance of perovskite photovoltaics. In chapter 10, interactions in formation kinetics of mixed-halide perovskites are systematically investigated.