Enhanced near-infrared detection in organic phototransistors via optimized donor–acceptor single crystals†

Organic single crystals are increasingly valued in organic phototransistors (OPTs) for their tunable properties and exceptional charge transport capabilities. However, their high exciton binding energy significantly limits dissociation efficiency. In this study, we successfully fabricated a high-performance near-infrared (NIR) CuPc OPT using PTCDA molecular doping, where CuPc acts as an electron donor matrix and PTCDA serves as an acceptor. Introducing PTCDA significantly enhances exciton dissociation, attributed to the numerous donor/acceptor interfacial barriers and the substantial energy level offset between CuPc and PTCDA. We found that a donor-to-acceptor ratio of 2 : 1 exhibits the optimal device performance, achieving a NIR responsivity of 500 A W⁻¹ at 850 nm and a response speed of 135 μs, far outperforming the isolated CuPc single crystal device. These results highlight the potential of molecular doping strategies for fabricating high-performance OPTs and provide insights for designing and optimizing organic single-crystal semiconductors (OSCSs) for advanced optoelectronic applications.