Development of Non-Fullerene-Based Electron Acceptors for Solar Cell Applications

The challenge of an increasing global energy demand and environmental consequences lead researchers to explore new alternative sources to conventional fossil or nuclear fuel sources. Photovoltaic devices exhibit one of the most promising approaches to generate electricity in a clean way. As an emerging technology in photovoltaic devices, organic solar cells (OSCs) have gained considerable attention due to their low-cost, flexibility, lightweight, and solution processability. Despite the fact that power conversion efficiencies (PCEs) of OSCs have exceeded 13%, significant effort is being implemented to design new materials with improved PCEs as well as to address device durability. Amongst solution-processed OPVs, fullerenes and their derivatives have been widely used as the highest performing electron acceptor component in solar cell devices. However, their low absorption in the solar spectrum, high-cost of synthesis and difficulties in their purification has lead researchers to look for alternative electron acceptors. Thus, non-fullerene acceptors can be alternative materials in solar cell devices for low-cost synthesis, tunable energy levels and providing complementary absorption to electron-donor polymer components, improving the photocurrent in devices. The main objective of this dissertation is to design and synthesise non-fullerene acceptor based conjugated small molecules using the core of IDTT and IDT as donor units and TPD and DPP as electron deficient moieties and explore their use as electron acceptor components in OSCs applications. The present study utilises numerous non-fullerene acceptor families obtained from direct arylation reactions, Stille cross-coupling and the Knoevenagel condensation reaction. The structure and elemental composition of the non-fullerene acceptors have been characterised by 1H NMR, elemental analysis and mass spectroscopy. The non-fullerene acceptors’ optical, thermal and electrochemical properties in solid state have been investigated to evaluate their suitability for organic photovoltaic devices application. The properties of the non – fullerene acceptors were found to be strongly dependent upon the use of TPD and DPP electron withdrawing moieties, as well as electron donating and other electron-deficient end capping moities.