Enhanced thermoelectric performance of pentacene via surface charge transfer doping in a sandwich structure

We demonstrate an enhanced electrical conductivity and power factor for pentacene based small-molecule organic thermoelectric (OTE) materials by constructing a PbI2/pentacene/PbI2 sandwich structure where the PbI2 serves as the surface transfer p-type dopant. The electronic structure evolution at interfaces between pentacene and PbI2 are investigated via in situ ultraviolet and x-ray photoelectron spectroscopy analysis. Significant charge transfer between pentacene and PbI2 is observed due to a high work function of PbI2 and a low ionization potential of pentacene. Such an interfacial charge transfer behavior results in efficient hole doping of pentacene from both sides. The increased hole density inside pentacene leads to the improvement in the thermoelectric performance, achieving a maximum power factor of 33.75 μW m−1 K−2 with an optimized pentacene interlayer thickness. This study opens a way to improve the OTE materials with the dopant/organic semiconductor/dopant sandwich structure.