• • Gradient thermal-annealing increased the exciton diffusion length (LD) from 19.47 nm (PM6-control) to 24.96 nm (PM6-target), a 28.2% enhancement that directly reduces exciton recombination losses and enables thicker active layers for scalable printing without sacrificing photocurrent.
• • The optimized crystallinity of PM6 inhibited film erosion by the upper acceptor solution, yielding a controlled pseudo planar heterojunction (PPHJ) with a non-radiative recombination loss of only 0.212 eV, which is critical for maintaining high open-circuit voltage in large-area modules.
• • The printed PPHJ device achieved a power conversion efficiency (PCE) of 18.20% with a fill factor of 78.2%, ranking among the top values for eco-friendly printing binary OPVs; this demonstrates that the gradient thermal-annealing strategy is compatible with roll-to-roll meniscus-guided coating (MGC) and non-halogenated solvents.
• • The PPHJ architecture, enabled by controlled donor-acceptor interpenetration, addresses the efficiency gap between small-area spin-coated devices and large-area printed modules, providing a viable pathway for industrial-scale manufacturing of organic photovoltaics with reduced environmental impact.