Organic solar cell (OSC) is one of the most promising third-generation solar cell technologies as organic solar modules are flexible, lightweight and semi-transparent, which can be produced by high-throughput roll-to-roll (R2R) printing processes. Indeed, the past few years have witnessed a significant advance in efficiency of non-fullerene acceptor (NFA) OSCs, which benefits from the emergence of outstanding materials. In this thesis, my research work focuses on designing and synthesizing donor and acceptor materials for achieving high-performance solar cells, paving a way for understanding the effect of molecular structures on morphological behaviour and device performance.

Chapter I introduces the background of OSCs, including the device types, photoelectric conversion mechanism, pho...[ Read more ]

Organic solar cell (OSC) is one of the most promising third-generation solar cell technologies as organic solar modules are flexible, lightweight and semi-transparent, which can be produced by high-throughput roll-to-roll (R2R) printing processes. Indeed, the past few years have witnessed a significant advance in efficiency of non-fullerene acceptor (NFA) OSCs, which benefits from the emergence of outstanding materials. In this thesis, my research work focuses on designing and synthesizing donor and acceptor materials for achieving high-performance solar cells, paving a way for understanding the effect of molecular structures on morphological behaviour and device performance.

Chapter I introduces the background of OSCs, including the device types, photoelectric conversion mechanism, photovoltaic parameters, molecular properties, morphological characterization and morphological optimization. Additionally, recent progress of OSC materials is summarized, especially the Y-type NFAs which are important stimulation for the development of OSCs.

Chapter II presents the random polymerization strategy to produce a series of terpolymers with various energy levels while maintain well-controlled morphology. These random copolymers are based on D-A1-D-A2 backbone of which the D and A1 units are building blocks from PM6 or PM7 while the A2 unit consists of an electron-poor core flanked by two thiophenes with 2- ethylhexyl chains. As a result, these random polymers yielded multiple high-performance OSCs with PCEs ranging from 16% to 17.1%. Indeed, there are a lot of moieties with other chemical structures that can serve as the A2 unit, which can produce many other polymers to match with different NFAs and fulfil their potential.

In Chapter III, we combined branched alkyl chain strategy and alkoxy chain strategy to develop a high-performance NFA based on the conjugated skeleton of Y6. The resulting molecule named Y6-O2BO demonstrated a much enhanced Voc of 0.96 V and highly ordered molecular packing pattern in the blend film, compared to the previously used branched alkyl or linear alkoxy modifications. It is noteworthy that Y6-O2BO exhibits an orderly molecular stacking and small π-π stacking distance in blend film, which could benefit for charge transport of device. The successfully synergistic modulation of the morphological and photovoltaic performance for NFA indicates that branched alkoxy chain is a promising strategy to design high-performance NFAs and thus accelerate the development of OSCs.

Chapter IV summarizes the content of this thesis and explores the challenges OSCs will confront in the future from the perspective of practical application in industry.