Crystallization Kinetics Directed by Additive Symmetry for Morphology Control in High‐Efficiency Organic Solar Cells

Why It Matters

By focusing on crystallization kinetics, manufacturers can achieve higher efficiencies and better reproducibility in organic photovoltaics, accelerating their path to commercial viability.

Key Takeaways

• 2,6-DBN additive yields 19.65% power conversion efficiency
• Symmetric additive promotes balanced crystallization during annealing
• Improved π–π stacking reduces energetic disorder in active layer
• Charge mobility increases, non‑radiative losses drop
• Kinetic control supersedes crystallinity as morphology lever

Pulse Analysis

Organic photovoltaics have attracted attention for their lightweight, flexible form factor and potential low‑cost manufacturing, yet their commercial viability hinges on achieving high power conversion efficiencies while maintaining reproducibility. The nanoscale morphology of the donor‑acceptor blend dictates exciton dissociation, charge transport, and ultimately device performance. Traditionally, solvent additives such as DIO or chlorobenzene derivatives are introduced to tune phase separation, but their high volatility can lead to batch‑to‑batch variation and long‑term degradation. Researchers therefore seek solid‑state additives that can reliably steer molecular ordering without compromising stability. Such solid additives also align with roll‑to‑roll coating processes favored by large‑area production.

The recent work on dibromonaphthalene (DBN) isomers demonstrates how subtle changes in additive symmetry can dominate crystallization kinetics in the benchmark PM6:Y6 system. Among the four positional isomers examined—1,8‑, 1,5‑, 2,7‑, and 2,6‑DBN—only the highly symmetric 2,6‑DBN delivers a moderate super‑cooling window that aligns with thermal annealing, enabling balanced ordering of the Y6 acceptor. This kinetic pathway produces compact π–π stacking, a favorable vertical phase gradient, and a measurable drop in energetic disorder, culminating in a record 19.65 % efficiency.

The implication is clear: controlling the rate of crystallization, rather than merely increasing additive crystallinity, offers a more reliable lever for morphology engineering across a range of non‑fullerene acceptors. This insight paves the way for designing solid additives with tailored symmetry and thermal behavior, potentially simplifying processing steps and improving long‑term device stability. As the organic solar market targets multi‑gigawatt scale deployment, such kinetic‑focused strategies could accelerate cost‑effective manufacturing while preserving the high efficiencies needed to compete with silicon photovoltaics.