SCIENCE CHINA Materials2026
Letting Polymer Semiconductors Crystallize Along Their Self-Templates: A Self-Templated Gradient Assembly Strategy for Multi-Scale Structural Ordering and Ultrahigh Charge Carrier Mobility
Polymer semiconductors offer solution processability, mechanical flexibility, and molecular tunability for flexible displays, wearable devices, and the Internet of Things, yet their charge transport properties remain substantially inferior to inorganic semiconductors. Efficient charge transport demands simultaneous structural order across molecular conformation, aggregate connectivity, and macroscopic orientation, but these length scales are strongly coupled: primary aggregates in solution, secondary nucleation during solvent evaporation, and final film solidification intertwine, rendering structural control dependent on empirical trial and error. Prior approaches—molecular design, solvent additives, thermal annealing, and shear coating—have improved crystallization and orientation, but two interrelated issues persist. First, enhancing aggregation does not guarantee higher mobility: insufficient aggregation yields small, loosely connected structures, while excessive aggregation causes premature nucleation, fiber twisting, and large grain boundaries. Second, direct observation of how solution aggregates evolve across molecular, mesoscopic, and macroscopic scales into solid films is often lacking. The fundamental challenge is not whether to promote crystallization, but how to cooperatively control aggregate type/size, internal order, connectivity, and assembly pathway, and to transform empirical solvent selection into predictive design rules. Zhao et al. report a self-templated gradient assembly (STGA) strategy that couples solubility parameters with vapor pressure to regulate both solution-state aggregation and assembly kinetics. Unlike conventional anti-solvent approaches that trigger rapid nucleation, STGA operates within mutually compatible solvent mixtures that retain polymer solubility and generate a continuous decline in solvent quality during evaporation. Preformed ordered aggregates become endogenous templates for subsequent assembly and crystallization rather than transient intermediates. Using a newly designed linear donor–acceptor polymer, PFIDTO-BT, and the relative energy difference (RED) index, cryogenic transmission electron microscopy confirmed that primary aggregates systematically enlarge as solvent quality decreases. Vapor pressure provides a second dimension, defining a solvent-selection matrix. For low-solubility, low-volatility components, the selectivity toward side chain/backbone parameter Ratio (S/B) further distinguishes aggregation pathways induced by different poor solvents. This framework connects solvent selection to hierarchical polymer organization through a semi-quantitative, experimentally testable methodology, enabling single-crystal-like polymer semiconductors with ultrahigh charge carrier mobility.
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