NiO_x Nanoparticles Hole-Transporting Layer Regulated by Ionic Radius-Controlled Doping and Reductive Agent for...

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.