Vertical Phase Separation in Blended Organic Semiconducting Films and Impact on Their Electrical and Direct X‐Ray Detection Properties

Blends of small-molecule organic semiconductors (OSCs) and insulating polymers in Organic Field-Effect Transistors (OFETs) are mainly used to assist the solution-processing of OSCs, but they can also reduce interfacial charge traps due to vertical phase separation. Such charge traps are known to affect both the electrical response and radiation-induced charge collection capability in these devices. This study aims to optimize vertical phase separation in blend films of 1,4,8,11-tetramethyl-%,13-triethylsilylethynyl pentacene (TMTES) and polystyrene (PS) to minimize charge trap density at the semicon- ductor/dielectric interface, thereby enhancing the electrical performance and direct X-ray detection sensitivity in OFETs. A PS mass concentration of 33% is identified as optimal for achieving high-quality phase separation and favorable film morphology. This formulation led to films with reduced interfacial hole trap density and improved electrical and detection capacity, demonstrating a hole field-effect mobility of (1.3 ± 0.4) cm( V−1 s−1 and X-ray sensitivity of ().% ± 0.() × 103 µC Gy−1 cm−( at low applied voltages. Remarkably, the molecular weight of PS does not significantly impact vertical phase separation, thin film morphology, or electrical properties. These findings are crucial for the devel- opment of high-performance OFETs and their application as X-ray detectors.