title: Quantitative analyses of enhanced thermoelectric properties of modulation-doped PEDOT:PSS/undoped Si (001) nanoscale heterostructures.
abstract: Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) has high electrical conductivity (∼103S cm-1) but it exhibits a low Seebeck coefficient (<15 μV K-1), resulting in a low power factor. Mixing PEDOT:PSS with nanostructured semiconductors can enhance the Seebeck coefficient and achieve an improved thermoelectric power factor. However, underlying mechanisms for those composite thermoelectric systems are scarcely understood so far. In this study, quantitative analyses on the electrical conductivity and Seebeck coefficient for the heterostructures of nanometer-thick PEDOT:PSS on single-crystal Si (001) on sapphire (SOS) are reported. The heterostructures have larger Seebeck coefficients up to 7.3 fold and power factors up to 17.5 fold relative to PEDOT:PSS. The electrical conductivity increased with decreasing combined thicknesses of PEDOT:PSS and Si, and the Seebeck coefficient increased with decreasing PEDOT:PSS thickness, which can be attributed to modulation doping caused by diffusion of holes from PEDOT:PSS into undoped Si. This hypothesis is supported by simulation per band alignment. The valence band offset between Si and PEDOT:PSS dominantly controls the electrical conductivity and Seebeck coefficient of the heterostructures. This study not only suggests mechanistic insights to increase the power factors of PEDOT:PSS-based composites but also opens the door for new strategies to enhance the thermoelectric efficiencies of heterostructured nanocomposite materials.
authors.affiliation: Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. shaohorn@mit.edu.
authors.forename: Dongwook
authors.initials: D
authors.lastname: Lee
authors.affiliation: The Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Sayed Youssef
authors.initials: SY
authors.lastname: Sayed
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. gchen2@mit.edu.
authors.forename: Sangyeop
authors.initials: S
authors.lastname: Lee
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. gchen2@mit.edu.
authors.forename: Chris Adam
authors.initials: CA
authors.lastname: Kuryak
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. gchen2@mit.edu.
authors.forename: Jiawei
authors.initials: J
authors.lastname: Zhou
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. gchen2@mit.edu.
authors.forename: Gang
authors.initials: G
authors.lastname: Chen
authors.affiliation: Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. shaohorn@mit.edu and The Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA and Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA. gchen2@mit.edu.
authors.forename: Yang
authors.initials: Y
authors.lastname: Shao-Horn