Hopping-Type Charge Transport in Controllably p-Doped Polaronic Two-Dimensional Polymers

In this work, we find that controllable p-type doping leads to Holstein-type polarons in four electron-rich two-dimensional polymers (2DPs). Substoichometrically injecting holes into these 2DPs leads to small optical bandgaps (<1.0 eV) and electrical conductivities (17 mS m^-1) significantly higher than their undoped analogs. Fourier-transform infrared spectroscopy and continuous-wave electron paramagnetic resonance spectroscopy both reveal that this arises from the formation of paramagnetic polarons. We achieve maximal conductivities when 2DPs comprised of electron-rich nodes and electron-rich linkers are combined, which is a consequence of more delocalized polarons as unveiled by diffuse-reflectance UV-vis-NIR spectroscopy. Variable-temperature electrical conductivity measurements reveal two distinct Arrhenius regimes in all 2DPs investigated, which we attribute to the different thermally activated processes inherent to in-plane and cross-plane electronic transport in stacked 2DP multilayers. This resulted in a maximum electronic conductivity of 326 mS m^-1 at an elevated temperature. Collectively, this report provides fundamental insight into polaron-based charge-transport in p-type 2D organic layers, which we expect will form the foundation for the eventual deployment of these materials in electronic devices.