Design, Synthesis and Investigation of Small-Molecule Materials for Organic Solar Cells

Among the various solar energy resources, organic solar cells (OSCs) are attracted attention of new technology owing to their advantageous features such as, cheaper manufacturing cost, light-weight, material diversity and mechanical flexibility, that render the interest of many research groups to develop such novel organic materials to design new device configurations. Recently, organic polymer solar cell and small-molecule organic solar cell both show fruitful device performance. 　　This dissertation describes my research effort in the design and synthesis of small-molecule materials with DAA and AADAA molecular configuration for OSCs followed by investigation of molecular structure to evaluate structure-property relationships, physical properties and device performance. The thesis is divided into four chapters and is organized as follow. Chapter 1 provides an introduction of basic principle of organic solar cell, the strategy of molecular design, and a short summary of state-of-the-art of small-molecule and polymer electronic donor materials for OSCs. In chapter 2, we synthesized silolo [3,2-b:4,5-b''] dithiophene, cyclopenta[1,2-b:5,4-b'']dithiophene, and benzo [1,2-b:4,5-b''] dithiophene-based AADAA structure organic dyes for solution process solar cell, and CPDT-T1 exhibited 0.80% efficiency. In chapter 3, we synthesized eight organic dyes with AADAA structure having variable electron withdrawing ability. The lowering of both HOMO and LUMO energy level cause enhanced device performance of vacuum-deposited organic solar cells, and thus CPDTBFC yielded 4.94% efficiency. In chapter 4, we synthesized a series of electron withdrawing thiazolidenemalononitrile-based DAA structure dyes with different diarylamine functionalities. Hole mobility of these compounds is found to be strongly dependent on the various intermolecular interactions. DPPT-based device has 3.52% efficiency of a PMHJ device without the thin donor layer.