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.