Exploring Disordered Morphologies of Blends and Block Copolymers for Light-Emitting Diodes with Mesoscopic Simulations

Abstract

Recently, disordered blends of semiconducting and insulating polymers have been used to prepare light-emitting diodes with increased luminous efficiency. Because the thermodynamic stability of the disordered phase in blends is limited, equivalent diblock copolymers (BCPs) could be an alternative. However, the choice between disordered blends and BCPs requires understanding structural differences and their effect on charge carrier transport. Using a hybrid mesoscopic model, we simulate blends and equivalent BCPs of two representative semiconducting and insulating polymers: poly(p-phenylene vinylene) (PPV) and polyacrylate. The immiscibility is varied to mimic annealing at different temperatures. We find stable or metastable disordered morphologies until we reach the mean-field (MF) spinodal. Disordered morphologies are heterogeneous because of thermal fluctuations and local segregation. Near the MF spinodal, segregation is stronger in BCPs than in the blends, even though the immiscibility, normalized by the MF spinodal, is the same. We link the spatial distribution of PPV with electric conductance. We predict that the immiscibility (temperature at which the layer is annealed) affects electrical percolation much stronger in BCPs than in blends. Differences in the local structure and percolation between blends and BCPs are enhanced at a high insulator content.

Can Soft Models Describe Polymer Knots?

“…Our mesoscopic description of homopolymer melts follows previous studies. 57 , 64 Let the melt contain n cg homopolymer chains in a volume V cg . The homopolymers are represented by discrete worm-like chains (WLCs).…”

“…The configurational space is sampled with PM Monte Carlo (MC) simulations, described in several previous studies. 53 , 55 , 57 , 64 In short, our simulations are performed in the canonical ensemble and consider cubic samples of melts with periodic boundary conditions (PBC). The edge of the cube equals ; this empirical choice is widely accepted as the minimum requirement for avoiding finite-system size effects in disordered melts.…”

Defects and defect engineering in Soft Matter

“…315 Morphological defects and aggregates in conjugated polymers can be controlled via controlling the processing of these polymers. 316,317 As mentioned before, one of the main advantages of conjugated polymers is the possibility of their processing (commonly making a thin film) by solution-based techniques. In this regard, controlling thin film morphology and related defects during printing or coating processes is critical due to its influence on device performance.…”

Direct synthesis of light-emitting triblock copolymers from RAFT polymerization

“…Semiconducting block-copolymers (BCPs) have attracted considerable attention for optical, optoelectronic and biomedical applications. [1][2][3][4][5] The reason for this is that BCPs combine two (or more) functionalities within a single polymer. Semiconducting BCPs may be all-conjugated, i.e.…”

“…11,12 BCPs are known for their capability to self-assemble or microphase separate into thermodynamically relaxed nanostructures, which can be tailored to suit various applications. 5,[13][14][15] The extent and dynamics of phase separation depend on block length and polarity, chain flexibility, glass transition temperature, etc. 16 If the contour length of the conjugated block is small relative to its persistence length, rod-coil BCPs are obtained for which additional contributions, such pi-stacking inter-actions, may give rise to non-classical morphologies, extending the portfolio of functional nanostructures.…”