• Additive-assisted layer-by-layer (LBL) deposition enables organic solar cells to achieve an unprecedented power conversion efficiency of 20.8%, the highest efficiency to date.
• The gradient fibrillar morphology enabled by additive-assisted LBL processing promotes the formation of bulk p-i-n structure, improving exciton and carrier diffusion, and reducing recombination losses.
• The wrinkle pattern morphology achieved by additive-assisted LBL processing is constructed to enhance the light capture capability.
• This approach offers a solution to achieving high-efficiency devices and demonstrates the potential for commercial applications of OSCs.