Tuning Dielectric Constant in Organic Semiconductors via Polar Molecule Doping for Tunable Photoresponse Speed and Anti‐Counterfeiting Application

Comprehensive Summary Organic phototransistors hold great promise for information optoelectronics due to their tunable molecular structures, inherent flexibility, and solution processability. However, their photoresponse speed is usually constrained by the high exciton binding energy and low carrier mobility of organic semiconductors. Here, we propose a simple and effective polar molecule doping strategy to tune the dielectric constant and photoresponse speed of organic semiconductors. By introducing polar small molecules, TPBi, into the polymer semiconductor PDVT‐10, the exciton binding energy is reduced through the dielectric screening effect, facilitating faster exciton dissociation. As a result, the doped organic phototransistors exhibit a remarkable reduction in photoresponse time from seconds to milliseconds while maintaining stable electrical performance. Furthermore, by integrating phototransistors with distinct response speeds, a programmable array is designed to achieve a dynamic anti‐counterfeiting application. This study presents a facile, universal, and scalable approach for tuning the photoresponse speed of organic semiconductors, offering new insights and design guidelines for high‐performance organic phototransistors and optical anti‐counterfeiting technologies.