Design and Synthesis of Active-Layer Materials for Efficient and Stable Organic Solar Cells

Doktorsavhandling, 2026

Organic photovoltaics (OPVs) have experienced rapid development over the past decade, with power conversion efficiencies (PCEs) rising from 10% to over 21% following the emergence of non-fullerene acceptors (NFAs), particularly Y-series acceptors. Despite these remarkable advances, the commercialization of OPVs is hindered by the high synthetic cost and complexity of high-performance active-layer materials, together with insufficient thermal and morphological stability. This thesis addresses these challenges through the molecular engineering of both acceptor and donor materials, with the aim of developing efficient, stable, and cost-effective organic solar cells (OSCs). A series of β-side-chain-free Y-series acceptors, including JSM5, JSM6, JSM19, and JSM7, was designed and synthesized. Eliminating the β-side chains substantially reduced synthetic complexity and enabled approximately one-third of material cost of their β-alkylated counterparts while exposing the central benzothiadiazole (BT) core to introduce additional core-to-core intermolecular interactions. These inter-core interactions led to enhanced molecular aggregation. Together with the improved blend crystallinity, binary OSCs based on JSM5 achieve comparable photovoltaic performance compared with Y6. The further quinoxaline modification of JSM5 enables enhanced device voltage and weakened self-aggregation for intermixed morphologies, delivering an improved PCE of 19.2%, among the highest PCEs reported for OSCs based on low-cost acceptors. This thesis also focuses on the development of amorphous donor polymers (PIDT-TxBT-series) with varied alkyl chains. When incorporated into OSCs with Y6 at a dilute donor-acceptor ratio of 1:10, these amorphous polymers significantly improved thermal and morphological stability compared with conventional PM6:Y6 and D18:Y6 systems, while maintaining competitive synthetic complexity. This work demonstrates that rational molecular design, including β-side-chain elimination, central-core modification, and the development of amorphous polymers, provides effective strategies for achieving both high efficiency and enhanced stability in devices, addressing critical barriers toward commercial viability.