Construction of Shamrock‐Shaped Giant Molecule Acceptors for Efficient Organic Solar Cells

Abstract The discovery of non‐fullerene small molecule acceptor materials has breathed new development into organic solar cells (OSCs). However, it has also introduced the issue of insufficient device stability. Enhancing the glass transition temperature ( T g ) of materials by connecting small molecules into giant molecules, thereby improving morphological stability, represents an effective material design strategy to address this issue. In this work, we have synthesized the shamrock‐shaped giant molecule materials T‐Qx based on high efficiency Qx‐series small molecule materials. Through systematically modulating the terminal and the central halogen atoms, precise control of the molecular conformation can be achieved. Notably, the fully chlorine‐substituted giant molecule T‐Qx‐15Cl exhibits the largest torsion angle of approximately 40° and achieves the highest T g (up to 188 °C) among these new materials. Photovoltaic devices based on these giant molecules demonstrate a low non‐radiative energy loss of approximately 0.21 eV, which results in a high open‐circuit voltage ( V oc ) above 0.93 V. T‐Qx‐15Cl presents the strongest interaction with the polymer donor PM6, achieving a power conversion efficiency (PCE) of more than 20%. This remarkable performance is attributed to the large twisting angle that effectively prevents the excessive aggregation of large π‐conjugated planar molecules.