Enhancing Molecular n‐Type Doping of Donor–Acceptor Copolymers by Tailoring Side Chains

Abstract

In this contribution, for the first time, the molecular n-doping of a donor-acceptor (D-A) copolymer achieving 200-fold enhancement of electrical conductivity by rationally tailoring the side chains without changing its D-A backbone is successfully improved. Instead of the traditional alkyl side chains for poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl](NDI)-alt-5,5'-(2,2'-bithiophene)} (N2200), polar triethylene glycol type side chains is utilized and a high electrical conductivity of 0.17 S cm after doping with (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine is achieved, which is the highest reported value for n-type D-A copolymers. Coarse-grained molecular dynamics simulations indicate that the polar side chains can significantly reduce the clustering of dopant molecules and favor the dispersion of the dopant in the host matrix as compared to the traditional alkyl side chains. Accordingly, intimate contact between the host and dopant molecules in the NDI-based copolymer with polar side chains facilitates molecular doping with increased doping efficiency and electrical conductivity. For the first time, a heterogeneous thermoelectric transport model for such a material is proposed, that is the percolation of charge carriers from conducting ordered regions through poorly conductive disordered regions, which provides pointers for further increase in the themoelectric properties of n-type D-A copolymers.

N‐Type Organic Thermoelectrics of Donor–Acceptor Copolymers: Improved Power Factor by Molecular Tailoring of the Density of States

“…The cyclic voltammetry characterization of PNDI2TEG‐2T and PNDI2TEG‐2Tz was carried out to investigate the effects of backbone modification on the energetics (see Figure S6, Supporting Information). This characterization confirms that the effect of the polar side chains (as compared to alkyl ones) on energetics is small (see Figure S6, Supporting Information), in accordance with our previous findings . The introduction of the electron‐deficient sp 2 ‐nitrogen atoms causes a shift of LUMO/HOMO level from −4.18/−5.39 eV for PNDI2TEG‐2T to −4.26/−5.56 eV for PNDI2TEG‐2Tz, which is consistent with the DFT calculation (Figure S7, Supporting Information).…”

“…As a result, electrical conductivities in the range of 1 × 10 −3 –5 × 10 −3 S cm −1 were achieved . Recent works demonstrated that the doping of D–A copolymers can be enhanced by increasing the host/dopant miscibility through the use of polar side chains . This can achieve an optimized electrical conductivity of up to 0.3 S cm −1 .…”

Highly Reproducible Sn‐Based Hybrid Perovskite Solar Cells with 9% Efficiency

“…The electrical conductivity (σ) was calculated according to the formula σ = (J/V) × L/(w × d), where d is the thickness of the perovskite films. The Seebeck coefficient was measured with a home-built setup [39] in a vacuum probe station. Temperature steps were imposed across the devices to measure the thermal voltages of perovskite thin films at different temperatures, which were detected by a standard constantan wire (127 µm from Omega, Seebeck coefficient of −39 µV K −1 ).…”

The Key Role of Side Chain Linkage in Structure Formation and Mixed Conduction of Ethylene Glycol Substituted Polythiophenes

“…Side-chain engineering of conjugated polymers (semiconductors) is one of the most powerful strategies to modify the properties such as crystallinity, charge transport and solubility of conjugated polymers. 1 Especially polar side chains are of great interest in conjugated polymers, because they create a permanent dipole, decrease the dielectric constant, reduce the π-π stacking distance, enable enhanced swelling, facilitating simultaneous ionic and electronic transport (mixed conduction) [2][3][4] . In specific examples, it was also demonstrated that this modification improves the doping efficiency due to the higher miscibility of dopant molecules within the hydrophilic side chains.…”