Dual‐Wavelength Control of Charge Accumulation in Rubrene Microcrystals with Anisotropic Conductivity

ABSTRACT

Previously, a novel type of rubrene microcrystals was reported, forming two distinct sectors–diamond‐ and triangular‐shaped–that exhibit pronounced contrasts in photoluminescence (PL) spectra and exciton dynamics. In the present work, their internal electronic structure is investigated using time‐of‐flight photoemission electron spectroscopy (TOF‐PES), revealing that the two sector's different charging characteristics arise from anisotropic conductivities. Upon photoemission via a one‐photon photoemission (1PPE) process excited by 6.2 eV (200 nm) photons, the diamond‐shaped sectors accumulate significant charge, whereas the triangular sectors remain essentially uncharged. The charge accumulation in the diamond sectors can be neutralized by additional sub‐threshold illumination, which generates charge carriers through internal photoeffect. The dynamics and energetics of the observed band shifting is described quantitatively by a model combining surface capacitance and drift‐diffusion. These crystalline systems enable the creation of built‐in charge landscapes that can be manipulated both spatially and temporally.