Iodinated Electron Acceptor with Significantly Extended Exciton Diffusion Length for Efficient Organic Photovoltaic Cells

Abstract Iodination has unlocked new potentials in organic photovoltaics (OPVs). A newly designed and synthesized iodinated non‐fullerene acceptor, BO‐4I, showcases exceptional excitation delocalization property with the exciton diffusion length increased to 80 nm. The enhanced electron delocalization property is attributed to the larger atomic radius and electron orbit of the iodine atom, which facilitates the formation of intra‐moiety excitations in the acceptor phase. This effectively circumvents the charge transfer state‐related recombination mechanisms, leading to a substantial reduction in non‐radiative energy loss (Δ E nr ). As a result, OPV cell based on PBDB‐TF : BO‐4I achieves an impressive efficiency of 18.9 % with a notable Δ E nr of 0.189 eV, markedly surpassing their fluorinated counterparts. This contribution highlights the pivotal role of iodination in reducing energy loss, thereby affirming its potential as a key strategy in the development of advanced next‐generation OPV cells.