Thermally Induced Neodymium‐Doped Strategy toward Wide Band Gap Perovskite Solar Cells with a Fill Factor over 86%

Abstract To approach the Shockley‐Queisser (S‐Q) limit in perovskite solar cells (PSCs), enhancing the fill factor (FF), a crucial parameter associated with carrier transport and nonradiative recombination, is of paramount importance. In this paper, the rare earths (RE), neodymium salt is used as dopant of 4‐(3‐,6‐dimethoxy‐9h‐carbazol‐9‐butyl) phosphonic acid (MeO‐4PACz) to obtain MeO‐4PACz:Nd³⁺, and Nd³⁺ migration is induced during annealing. It is worth noting that the uniform diffusion of Nd³⁺ in the perovskite layer significantly increases the defect‐formation energy of perovskite, thus reducing the density of the perovskite defect states, greatly improving the carrier transport rate and inhibited non‐radiative recombination. The experimental results show that the wide‐band gap (WBG) PSCs based on MeO‐4PACz:Nd³⁺ has an excellent power conversion efficiency (PCE) of 22.82% with the FF of 86.35%. The proposed method provides a direct method for RE³⁺ to promote the FF of perovskites.