Unified Understanding of Molecular Weight Dependence of Electron Transport in Naphthalene Diimide-Based n-Type Semiconducting Polymers

Abstract

Electron transport is critical to the use of n-type semiconducting polymers in diverse electronic and optoelectronic devices. Herein, we combine measurements of field-effect electron mobility and bulk electron mobility with thin-film microstructure characterization to elucidate the polymer chain length dependence of electron transport in n-type semiconducting polymers, exemplified by a naphthalene diimide-biselenophene copolymer, PNDIBS. Both bulk electron mobility measured by the space–charge limited current method and field-effect electron mobility of PNDIBS and other n-type semiconducting copolymers exhibit a peak at a critical degree of polymerization (DPc) of 45–60 repeat units. The decreased electron mobility below DPc is shown to originate from reduced intercrystallite connectivity while above DPc, intrachain twisting/folding, interchain entanglements, and intracrystallite limitations dominate electron transport. These findings provide a unified picture of the effects of polymer molecular weight on electron transport in naphthalene diimide-based polymers and offer a more quantitative design rule for high-mobility n-type polymers with donor–acceptor architecture.

Ambipolar Charge Transport in p-Type Cyclopentadithiophene-Based Polymer Semiconductors Enabled by D–A–A–D Configuration

“…Their corresponding polydispersity indices (PDIs) were 3.57 and 1.74. Although the M n of P2 was less than that of P1 presumably due to the steric hindrance of monomer 4 (discussed later), the value was sufficiently high for efficient charge transport in its solid state …”

“…Although the M n of P2 was less than that of P1 presumably due to the steric hindrance of monomer 4 (discussed later), the value was sufficiently high for efficient charge transport in its solid state. 33 2.2. Optical and Electrochemical Properties.…”

Unraveling the Effect of Stereoisomerism on Mobility–Stretchability Properties of n-Type Semiconducting Polymers with Biobased Epimers as Conjugation Break Spacers

“…The entropies of fusion (Δ S f ) are calculated using the formula Δ S f = Δ H f / T m , and the Δ S f values of ISB , IMN , IID , and C4 are 0.025, 0.010, 0.004, and 0.018 J g –1 K –1 , respectively. Δ S f indicates that the number of configurations changes between the crystal and melt states, which can be represented as Δ S f = S melt – S crystal = k (ln Ω melt – ln Ω crystal ), where k is the Boltzmann constant and Ω is the possible configuration of the polymer chain . Therefore, a larger Δ S f value implies a decrease in entropy and conformation in the crystalline state, enabling efficient interchain and intrachain packing.…”

“…ΔS f indicates that the number of configurations changes between the crystal and melt states, which can be represented as ΔS f = S melt − S crystal = k(ln Ω melt − ln Ω crystal ), where k is the Boltzmann constant and Ω is the possible configuration of the polymer chain. 48 Therefore, a larger ΔS f value implies a decrease in entropy and conformation in the crystalline state, enabling efficient interchain and intrachain packing. The high planarity and strong aggregation of the CBSs in ISB and C4 are associated with larger ΔS f values, which likely facilitate efficient packing.…”

Chain Length Dependence of Electron Transport in an n-Type Conjugated Polymer with a Rigid-Rod Chain Topology

“…The observed continuous growth of electron mobility with polymer chain length in the rigid-rod ladder polymer, BBL, is to be contrasted with the chain length dependence of electron transport properties of semiflexible n-type semiconducting polymers 34,42,43 and hole transport properties of semiflexible ptype semiconducting polymers. [24][25][26][27][28][29][30][31][32][33]44 In particular, the charge carrier mobilities of semiflexible polymers, be it hole or electron, reach a maximum at relatively small DP values (Figure S1) due to the structural disorder arising from the semiflexible backbone and their long alkyl side chains.…”