Resistive Heating for Inducing Localized Crystal Growth in Organic Thin Film Devices

Abstract Crystalline organic semiconductors are crucial for high‐performance optoelectronic devices due to their potential for high charge‐carrier mobility. Rubrene, in particular, exhibits exceptional hole transport in crystalline thin films; however, conventional thermal annealing methods often promote uncontrolled crystallisation and grain boundary formation, hindering lateral transport and device scalability. Here, a flexible femtosecond laser micromachining strategy is introduced to achieve localized crystallization and precise structural control in rubrene thin films. By utilizing a 200 fs laser at 514 nm, three laser‐based techniques are explored: defect seeding, spatially confined annealing, and micro‐patterned ablation – along with resistive heating using patterned indium tin oxide (ITO) substrates to induce and restrict crystal growth. Among these approaches, the resistive heating approach effectively enables deterministic crystallization with high spatial resolution, allowing for the formation of regularly spaced or isolated crystals. The findings outline a pathway for integrating localized crystallization techniques into device fabrication, offering new opportunities to reduce crosstalk and facilitate the miniaturization of organic electronic and optoelectronic systems.