NiO_x Nanoparticles Hole‐Transporting Layer Regulated by Ionic Radius‐Controlled Doping and Reductive Agent for Organic Solar Cells with Efficiency of 19.18%

Abstract Nickel oxide (NiO_x) has garnered considerable attention as a prospective hole‐transporting layer (HTL) in organic solar cells (OSCs), offering a potential solution to the stability challenges posed by traditional HTL, PEDOT:PSS, arising from acidity and hygroscopicity. Nevertheless, the lower work function (WF) of NiO_x relative to donor polymers reduces charge injection efficiency in OSCs. Herein, NiO_x nanoparticles are tailored through rare earth doping to optimize WF and the impact of ionic radius on their electronic properties is explored. Lanthanum (La³⁺) and yttrium (Y³⁺) ions, with larger ionic radii, are effectively doped at 1 and 3%, respectively, while scandium (Sc³⁺), with a smaller ion radius, allows enhanced 5% doping. Higher doping ratios significantly enhance WF of NiO_x. A 5% Sc³⁺ doping raises WF to 4.99 eV from 4.77 eV for neat NiO_x while maintaining high conductivity. Consequently, using 5% Sc‐doped NiO_x as HTL improves the power conversion efficiency (PCE) of OSCs to 17.13%, surpassing the 15.64% with the neat NiO_x. Further enhancement to 18.42% is achieved by introducing the reductant catechol, outperforming the PEDOT:PSS‐based devices. Additionally, when employed in a ternary blend system (D18:N3:F‐BTA3), an impressive PCE of 19.18 % is realized, top‐performing among reported OSCs utilizing solution‐processed inorganic nanoparticles.