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Shift of the Branching Point of the Side‐Chain in Naphthalenediimide (NDI)‐Based Polymer for Enhanced Electron Mobility and All‐Polymer Solar Cell Performance
Author(s) -
You Hoseon,
Kim Donguk,
Cho HanHee,
Lee Changyeon,
Chong Sanggyu,
Ahn Nam Young,
Seo Myungeun,
Kim Jihan,
Kim Felix Sunjoo,
Kim Bumjoon J.
Publication year - 2018
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201803613
Subject(s) - branching (polymer chemistry) , materials science , side chain , steric effects , polymer , conjugated system , acceptor , electron acceptor , intermolecular force , electron , polymer chemistry , polymer solar cell , photochemistry , stereochemistry , molecule , organic chemistry , chemistry , condensed matter physics , physics , composite material , quantum mechanics
Abstract The branching point of the side‐chain of naphthalenediimide (NDI)‐based conjugated polymers is systematically controlled by incorporating four different side‐chains, i.e., 2‐hexyloctyl (P(NDI1‐T)), 3‐hexylnonyl (P(NDI2‐T)), 4‐hexyldecyl (P(NDI3‐T)), and 5‐hexylundecyl (P(NDI4‐T)). When the branching point is located farther away from the conjugated backbones, steric hindrance around the backbone is relaxed and the intermolecular interactions between the polymer chains become stronger, which promotes the formation of crystalline structures in thin film state. In particular, thermally annealed films of P(NDI3‐T) and P(NDI4‐T), which have branching points far away from the backbone, possess more‐developed bimodal structure along both the face‐on and edge‐on orientations. Consequently, the field‐effect electron mobilities of P(NDI m ‐T) polymers are monotonically increased from 0.03 cm 2 V −1 s −1 in P(NDI1‐T) to 0.22 cm 2 V −1 s −1 in P(NDI4‐T), accompanied by reduced activation energy and contact resistance of the thin films. In addition, when the series of P(NDI m ‐T) polymers is applied in all‐polymer solar cells (all‐PSCs) as electron acceptor, remarkably high‐power conversion efficiency of 7.1% is achieved along with enhanced current density in P(NDI3‐T)‐based all‐PSCs, which is mainly attributed to red‐shifted light absorption and enhanced electron‐transporting ability.