Enhanced Optoelectronic Performance of Two-Dimensional Organic Semiconductor Phototransistors Using Polystyrene Microsphere-Based Light-Trapping Structures

Two-dimensional organic semiconductor crystals (2DOSC) possess excellent flexibility, extraordinary charge transport ability, and tunable optoelectronic properties, which have attracted continuous research interest due to their tremendous potential in electronic and optoelectronic applications. Organic phototransistors (OPT) based on 2DOSC can achieve ultralow dark current, significantly improving the optoelectronic performance of the OPTs. However, the low light utilization efficiency of 2DOSC and the extremely limited photocurrent enhancement hinder further development and application. Therefore, improving the light utilization efficiency of 2DOSC is crucial to enhancing its optoelectronic performance. Here, we proposed a light-trapping structure (PS-LTS) based on polystyrene (PS) microspheres, which significantly enhanced the optoelectronic performance of the OPTs based on 2-Decyl-7-phenyl[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-C10) 2DOSC (PS-LTS/Ph-BTBT-C10 OPT). Building on the low noise current provided by the 2D organic semiconductor (2DOSC), the introduction of the PS-LTS structure improved light utilization efficiency, reduced exciton binding energy, and enhanced charge carrier transport, thereby achieving higher optoelectronic response values. By adjusting the concentration of the PS microsphere dispersion, the I_light/I_dark ratio of the PS-LTS/Ph-BTBT-C10 OPT was increased by several orders of magnitude, while the key optoelectronic performance indicators such as responsivity (R), photosensitivity (P) external quantum efficiency (EQE), and detectivity (D*) are improved by 2 orders of magnitude. Our findings provide a pathway for designing novel OPT structures to enhance optoelectronic response and offer the potential for the future development of low-cost, high-performance organic photodetectors.