2D In-Plane Molecular Superlattice Heterojunctions for High-Performance Ambipolar Electronics and Low-Dose X-Ray Sensing.

Abstract

Two-dimensional in-plane molecular superlattice heterojunctions, where distinct semiconducting components are integrated laterally within a single crystalline plane, offer an ideal architecture for controlling charge separation and transport in optoelectronic devices. However, realizing such structures with molecular-level precision, long-range periodicity, and sharp interfaces in organic semiconductors remains a major challenge. Here, the first 2D organic heterojunction featuring long-range, in-plane donor-acceptor superlattice via cocrystal engineering is presented. By employing phase-separated molecular design for the donor (TIPS-PEN) and acceptor (PDI-FCN), strong in-plane cohesion is decoupled from out-of-plane steric repulsion, inducing a periodic -D-A-D- arrangement within the crystal plane. The resulting high-density, lattice-defined heterointerfaces facilitate exciton dissociation, directional charge transport, and efficient extraction. The ultrathin crystal enables effective gate-field control, yielding ambipolar OFETs with exceptional on/off ratios of 10⁸ (holes) and 10⁷ (electrons). Capitalizing on the narrow bandgap and the ordered 2D heterointerface, this material demonstrates outstanding high-energy photon conversion efficiency. As an X-ray detector, it exhibits high sensitivity of 4.21 × 10⁴ µC Gy^-1 cm^-2 and low detection limit 5.73 nGy s^-1, enabling clear imaging at 14.77 nGy s^-1 ultralow dose rate. This work provides new ideas for constructing 2D multicomponent organic heterostructures and unlocks potential for next-generation flexible electronics and low-dose radiation sensing.