Enhancement of the ThermoelectricPerformance ofn-Type Naphthalene Diimide-Based Conjugated Polymer by Engineering ofSide Alkyl Chains

Developingn-type doped semiconducting polymers with highthermoelectric (TE) performance still remains challenging. In this paper, weshow a new strategy to enhance the TE performance ofn-doped naphthalenediimide (NDI)-based conjugated donor-acceptor (D-A) polymer by introduc-ing one linear alkyl chain for each NDI unit. Film of the PNDI2T-1, in whicheach NDI unit is attached with one linear and one branching alkyl chains,exhibits higher electrical conductivity and a greater power factor (PF) thanthose of PNDI2T-2 with the same conjugated backbone and two branching sidechains, after doping with either (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimida-zol-2-yl)phenyl)dimethylamine (N-DMBI) or decahydro-3a,6a,9a-triazaphena-lene (TAM) under the same conditions. The optimal PF values of the dopedfilms of PNDI2T-1 withN-DMBI and TAM can reach 1.6 and 3.5 mu Wm-1K-2,respectively, which are among the highest reported TE performances for NDI-based semiconducting polymers aftern-doping. The higher TE performance of the dopedfilms of PNDI2T-1 is attributed tothe enhancement of charge mobility and improvement of doping degree after side-chain modification. These results provide anew molecular design rationale for the future development of high-performancen-type thermoelectric semiconductingpolymers.

Automated summary

In this study, a new strategy to enhance the thermoelectric performance of n-doped semiconducting polymers was demonstrated. The introduction of linear alkyl chains in a conjugated donor-acceptor polymer based on n-doped naphthalenediimide (NDI) led to films with higher electrical conductivity and power factor. These results provide a new molecular design rationale for the future development of high-performance n-type thermoelectric semiconducting polymers.