Harnessing Atomic-Scale Thinning in Two-Dimensional Organic Molecular Crystals for In-Situ Characterization and...

Two-dimensional organic single crystals (2D OSCs) offer high crystallinity and quantum limit properties, making them ideal for exploring unique quantum phases and developing scaled optoelectronic devices. However, accurately probing the structure-optoelectronic relationship in 2D OSCs remains challenging. Here we realize in situ optoelectronic characterization of 2D OSCs through an atomically precise thinning technique. Thinning 3D pentacene crystals to the monolayer limit induces a phase transition from Frenkel excitons to charge-transfer (CT) excitons, achieving a near-unity quantum yield (∼95.1%). In-situ electrical measurements demonstrate that this thinning improves carrier mobility and reduces threshold voltages. Utilizing 2D pentacene crystals, we construct a high-performance synapse device, showing a record paired-pulse facilitation index (PPF index ∼ 261%). This remarkable synaptic plasticity further allows us to emulate the human vision system, predicting the object trajectory with exceptional accuracy (∼99.1%). These results provide new insights into the intrinsic properties of 2D OSCs and lay the foundation for multifunctional optoelectronic applications.