Thermoelectric Properties of an Indandione-Terminated Quinoidal Compound: Effect of the n-Type Dopants

The investigation of n-type doping holds a significant interest for the application of thermoelectrics. Herein, the doping of an indandione-terminated compound Q-4F with a singlet open-shell ground state was studied using two n-dopants N-DMBI and LCV. Both of these two dopants can effectively dope Q-4F due to the large offset between the singly occupied molecular orbital (SOMO) of dopants and the lowest unoccupied molecular orbital (LUMO) of Q-4F. N-DMBI has a higher doping ability than LCV as demonstrated by the UV-vis-NIR and EPR measurements. However, in comparison to N-DMBI doped Q-4F, LCV doped system exhibits much higher electrical conductivity and power factor due to its unperturbed molecular packing and favorable morphology after doping. The optimal conductivity of LCV doped Q-4F is 7.16 x 10-2 +/- 0.16 S.cm(-1) and the highest power factor reaches 12.3 +/- 0.85 mu W.m(-1).K-2. These results demonstrate that the modulation of n-dopants is a powerful strategy to balance the doping efficiency and microstructure toward a maximum thermoelectric performance.