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

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.