Molecular design for controlling morphology in organic electronics

Abstract

Chapter 1 gives an introduction to the structure, operation mechanism, performance parameters, and challenges of organic photovoltaic devices. We also discuss some strategies to improve the performance of photovoltaics, with an emphasis on morphology control in polymer bulk-heterojunction devices. Chapter 2 describes the synthesis of a class of polymer additives for bulk-heterojunction (BHJ) solar cells based on an extended triptycene-containing unit. The incorporation of these additives on BHJ photovoltaic devices based on PTB7 and PC71BM leads to an increase in power conversion efficiencies of 10-20%. We also found that the additives produce more consistent performance in devices, minimizing variation from processing conditions. Chapter 3 presents a modular synthetic route to access functionalized 2,5-di(thiophen-2- y1)- 1-H-arylpyrroles (SNS) from readily available starting materials. We demonstrated the use of this building block in the synthesis of conjugated polymers with high thermal stability and solubility. Characterization of the polymers reveals a correlation between molecular packing and charge carrier mobility. Chapter 4 discusses strategies to enhance conjugation in organic electronic materials, using 2,5-di(thiophenyl)-N-arylpyrrole (SNS) as a model system. The first section describes synthetic routes to access a novel polycyclic heteroaromatic building block via intramolecular cyclization reactions. The second section explores the electrochemical properties of SNS units for the opportunity to enhance conjugation via electrochemical methods.