π-Extended chlorinated non-fullerene acceptors for achieving high performance organic solar cells

Abstract

The photovoltaic properties and energy loss of organic solar cells (OSCs) based on non-fullerene acceptors (NFAs) are highly dependent on their molecular structures and morphologies. Herein, three NFAs, named F′-2Cl, F′-NCl and F′-N2Cl with different end groups, are designed and synthesized by adopting π-extension and chlorination modifications. As a result, a favorable morphology is achieved in a PM6:F′-N2Cl based OSC and this system exhibits the highest power conversion efficiency (PCE) of 14.13% with a J_sc of 20.31 mA cm⁻², a V_oc of 0.927 V and a FF of 74.68%. Extending the conjugation of the end group narrows the molecular bandgaps and enables a lower E_loss of 0.686 and 0.706 eV with nonradiative recombination losses of as low as 0.207 and 0.203 eV in F′-NCl and F′-N2Cl based devices, respectively. This work provides an efficient strategy to optimize the molecular structures of non-fullerene acceptors and further improve the properties of OSCs.