Thermal-Assisted Fracture Healing Realizing High-Accuracy Polymer Crack Lithography

Polymer crack lithography, spontaneously performed through stress-induced film fracturing, offers a time-efficient and low-cost template method for functional material patterning. However, achieving high patterning accuracy is challenging due to unpredictable interfacial fractures. These defects compromise template fidelity by allowing for electrolyte infiltration beneath the warped polymer film, leading to uncontrolled deposition and significant deviations from the designed pattern. To address this, we developed a thermal post-treatment strategy that promotes fracture healing by activating polymer chain mobility at temperatures modestly above the material glass transition temperature (T_g). This method significantly improved template fidelity in copper (Cu) electroplating, reducing the width deviation between fabricated patterns and designed templates from 11.1 μm (uncontrolled fractures) to 0.1 μm (healed fractures) by suppressing electrolyte infiltration. The optimized Cu patterns could be easily transferred onto the polydimethylsiloxane (PDMS) film and exhibit enhanced transmittance (77% vs 66.8% untreated) with a sheet resistance of 0.3 Ω/sq. Consequently, the optoelectronic figure of merit (σ_DC/σ_OPT) improves by 18-fold. Furthermore, through cobalt sulfide (CoS), electrocatalytic network fabrication achieved a high AM1.5G weighted average transmittance (T̅ ) of 74.5% and charge transfer efficiency (R_ct = 5.45 Ω·cm²). Applied as transparent electrodes in bifacial solar cells, these CoS networks enabled 79% back-to-front efficiency retention. This low-temperature (50 °C) post-treatment enhances polymer crack lithography accuracy while maintaining its rapid processing advantages, demonstrating broad applicability for functional materials in advanced optoelectronic devices.