Non-fullerene acceptor with asymmetric structure and phenyl-substituted alkyl side chain for 20.2% efficiency organic solar cells

For organic solar cells (OSCs), bridging the gap with Shockley-Queisser limit necessitates simultaneously reducing the energy loss for a high open-circuit voltage, improving light utilization for enhanced short-circuit current density and maintaining ideal nanomorphology with a high fill factor through molecular design and device engineering. Here we design and synthesize an asymmetric non-fullerene acceptor (Z8) featuring tethered phenyl groups to establish an alloy acceptor in ternary OSCs. The asymmetric structure minimizes non-radiative energy loss and charge recombination owing to delocalized excitons. The phenyl-substituted alkyl side chain impacts on the intermolecular interactions, improving the film nanomorphology with efficient exciton dissociation and reduced charge recombination. We demonstrate OSCs with an efficiency of 20.2% (certified 19.8%) based on the D18:Z8:L8-BO ternary blend. Through theoretical calculations, we examine the overall distribution of photon and carrier losses and analyse the potential for improvement on open-circuit voltage, short-circuit current density and fill factor, providing rational guidance for further development of the OSC performance. Molecular design is key to the power conversion efficiency in organic photovoltaics. Jiang, Sun, Xu et al. develop a non-fullerene acceptor with asymmetric structure and phenyl-substituted side chains that minimizes photon and carrier losses, enabling 20.2% efficiency.