Fabricating high‐efficient electron transporting interfacial layers (ETLs) with isotropic features is highly desired for all‐directional electron transfer/collection from an anisotropic active layer, achieving excellent power conversion efficiency (PCEs) on nonfullerene acceptor (NFA) organic solar cells (OSCs). The complicated synthesis and cost‐consumption in exploring versatile materials arouse great interest in the development of binary‐doping interlayers without phase separation and flexible manipulation. Herein, for the first time, a novel cathode interfacial layer based on biomass‐derived demethylated kraft lignin (DMeKL) is proposed. Features of multiple phenolic‐hydroxyl (PhOH) and uniform‐distributed render DMeKL to exhibit an excellent bonding capacity with amino terminal substituted perylene diiminde (PDIN), and successfully form a high‐efficient isotropic electron transfer 3D network. Synchronously, secondary bonds completely modify conjugate‐blocked linkages of DMeKL, significantly enhance the electron transporting performance on cross‐section and vertical‐sections, and repair the contact of PDIN with active layer. The DMeKL/PDIN‐based 3D‐network exhibits well‐matched work function (WF) (–4.34 eV) with cathode (–4.30 eV) and energy level of electron acceptor (–4.11 eV). DMeKL/PDIN‐based NFAs‐OSC shows excellent short‐circuit current density (26.61 mA cm–2) and PCE (16.02%) beyond the classic PDIN‐based NFA‐OSC (25.64 mA cm–2, 15.41%), which is the highest PCEs among biomaterials interlayers. The results supply a novel method to achieve high‐efficient cathode interlayer for NFAs‐OSCs.