Fluorene-Based Two-Dimensional Covalent Organic Framework with Thermoelectric Properties through Doping

Organic semiconductors have great potential as flexible thermoelectric materials. A fluorene-based covalent organic framework (FL-COF-1) was designed with the aim of creating an enhanced π-π interaction among the crystalline backbones. By the introduction of fluorene units into the frameworks, the FL-COF-1 had high thermal stability with a BET surface area over 1300 m² g^-1. The open frameworks were favorable for doping with iodine and followed with the improved charge carrier mobility. The compressed pellet of I₂@FL-COF-1 exhibited a high Seebeck coefficient of 2450 μV K^-1 and power factor of 0.063 μW m^-1 K^-2 at room temperature, giving the first example of COFs' potential application as thermoelectric materials.