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

Abstract

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-6,13-triethylsilylethynyl pentacene (TMTES) and polystyrene (PS) to minimize charge trap density at the semiconductor/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) cm² V⁻¹ s⁻¹ and X-ray sensitivity of (5.6 ± 0.2) × 10³ µC Gy⁻¹ cm⁻² 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 development of high-performance OFETs and their application as X-ray detectors.