Exceptional electron conduction in two-dimensional covalent organic frameworks

Abstract

<h2>Summary</h2> Most organic/polymeric semiconductors are <i>p</i>-type semiconductors, whereas their <i>n</i>-type versions are limited in both availability and carrier mobility. How to develop high-rate <i>n</i>-type organic/polymeric semiconductors remains challenging. Here, we report an approach to high-rate <i>n</i>-type semiconductors via topology-directed polycondensation of conventional <i>p</i>-type knots with <i>n</i>-type isoindigo linkers to form non-conjugated tetragonal and hexagonal two-dimensional polymeric frameworks. The polymers are planar in conformation and show flattened frontier levels, which enable electrons to move along the non-conjugated polymeric backbones. The eclipsed face-to-face stack reduces reorganization energy and greatly strengthens electronic coupling, thus enabling band-like electron conduction perpendicular to polymer layers. A device recording electron mobility as high as 8.2 cm² V⁻¹ s⁻¹ was achieved with Hall effect measurements, whereas time- and frequency-resolved terahertz spectroscopy revealed a benchmark mobility of 13.3 cm² V⁻¹ s⁻¹. These new mechanistic insights with exceptional mobility open the way to high-rate <i>n</i>-type organic/polymeric semiconductors.