The PCPDTBT Family: Correlations between Chemical Structure, Polymorphism, and Device Performance

Abstract

We highlight the influence of processing conditions on polymorphism and structure formation on the mesoscale for the family of PCPDTBT polymers with branched alkyl side chains. Direct correlations of morphology to the chemical structure and to transistor device performance are established. We found that up to four different packing motifs could be realized depending on the polymer derivative and the processing conditions: amorphous, -stacked, cross-hatched and dimer-containing polymorphs. While C-and F-PCPDTBT display similar packing behavior organizing in -stacked and dimer-like structures, Si-PCPDTBT gives rise to cross-hatched structures upon simple deposition from solution. The observed differences in chain packing for C-/F-PCPDTBT versus Si-PCPDTBT are related to differences in backbone conformations and aggregation behavior in solution. The effect of polymorphism on charge transport is probed using field-effect transistors, in which both -stacked and cross-hatched polymer chain arrangements yield the highest hole mobilities. Structural and mobility simulations rationalize our experimental findings by relating mobility to distributions of electronic coupling elements between the chains.

Controlled Crystallization of Conjugated Polymer Films from Solution and Solvent Vapor for Polymer Electronics

“…For comparison to C‐PCPDTBT, the thin film absorption spectra of Si‐PCPDTBT (M n = 11.0 kg mol ‐1 and PDI = 2.9) deposited from CHCl 3 and CB are shown in Figure b . While the overall shape of the spectra is similar to the carbon analogue, Si‐PCPDTBT shows regardless of solvent, a very pronounced aggregation shoulder at 760 nm . Our data indicate that the morphology (not shown) of Si‐PCPDTBT is much more dominated by aggregation in solution than in the case of C‐PCPDTBT.…”

“…c) AFM height image of C‐PCPDTBT thin film spin coated from CB/DIO. d) Bilayer solar cell device architecture, e) field‐effect transistor device structure, f) J‐V curves of the solar cells and g) FET hole mobilities of the two polymorphs . Reproduced and adapted with permission .…”

“…The charge transport properties of the two different polymorphs: dimer and long‐range π‐stacked, were investigated using field‐effect transistors consisting of a top gate, bottom‐contact architecture (see Figure e) . This device architecture was employed since the same polymer interface investigated in AFM is probed during transistor operation.…”

Charge transport in high-mobility conjugated polymers and molecular semiconductors

“…These typically involve the steps of simulating realistic morphologies by molecular dynamics, partitioning into conjugation segments, calculating molecular charge transfer rates for pairs of conjugation segments and simulating the charge dynamics by master equation or kinetic Monte Carlo methods 75,76 . These methods were first applied to molecular systems such as discotic liquid crystals 77 , but have since also been shown to provide realistic estimates of carrier mobilities in conjugated polymers, including P3HT 78 , PBTTT 79,80 or the D-A copolymer PCPDTBT 81 . For PBTTT it was shown that the fluctuations in the transfer integrals (that is, dynamic disorder) occur mostly on timescales of <100 fs, which are faster than the timescale for charge transfer.…”

Conjugated polymer single crystals and nanowires

“…The structure of D‐A conjugated polymers is rather complex. Nanowires or nanofibers of several D‐A conjugated polymers had been reported . For example, Mullen et al prepared cyclopentadithiophene‐benzothiadiazole copolymer (CDT‐BTZ) nanowires by solvent vapor enhanced drop casting .…”