Enhanced Thermoelectric Performance of Iodine-Doped Metal-Free Phthalocyanine

Metal phthalocyanine compounds are considered promising organic thermoelectric materials due to their high carrier mobility and Seebeck coefficient. However, their relatively low carrier concentration and electrical conductivity represent bottlenecks limiting the development of metal phthalocyanine-based thermoelectrics. Here, a series of Iodine-doped phthalocyanine (H2PcI) samples were prepared through vapor-phase reaction, and the influence of iodine doping on their electrical transport properties was systematically investigated. Analysis results from scanning electronic microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction indicate that during the reaction between iodine and hydrogen phthalocyanine, electrons are transferred from the phthalocyanine ring to iodine atoms, and iodine exists in the form of triiodide ions (I3–). The electrical conductivity of H2PcI from room temperature to 400 K is increased by 8–9 orders of magnitude compared to pure H2Pc, reaching 315 S·m–1 at 350 K. This study demonstrates that the vapor-phase reaction is an effective approach for achieving high-concentration doping in organic small molecules. It provides valuable insights into doping strategies applicable to other organic small-molecule crystalline materials.