Bilayer order in a polycarbazole-conjugated polymer

Abstract

one of the best performing semiconducting polymers used in bulk heterojunction devices is PCDTBT, a polycarbazole derivative with solar-conversion efficiencies as high as 7.2%. Here we report the formation of bilayer ordering in PCDTBT, and postulate that this structural motif is a direct consequence of the polymer's molecular design. This bilayer motif is composed of a pair of backbones arranged side-to-side where the alkyl tails are on the outer side. This is in stark contrast to the monolayer ordering found in other conjugated polymers. The crystalline bilayer phase forms at elevated temperatures and persists after cooling to room temperature. The existence of bilayer ordering, along with its high-packing fraction of conjugated moieties, may guide the synthesis of new materials with improved optoelectronic properties.

Morphology Development in Amorphous Polymer:Fullerene Photovoltaic Blend Films During Solution Casting

“…We identify scattering at this Q value as originating from PCDTBT, specifically fi rst order scattering between neighbouring chains along the lamella direction. [34][35][36] Here, the weak signal intensity refl ects both the semi-amorphous nature of the polymer and its low concentration (20 wt%) in the blend fi lm. We highlight the three key stages in the process determined by our measurements.…”

“…Typically, as-cast fi lms of PCDTBT are relatively amorphous, having a characteristic lamella spacing of approximately 20.9 Å and a π -π stacking distance of approximately 4.4 Å. [34][35][36] In Figure 4 (a) it can be seen that a broad peak centred at Q = 0.32 Å −1 ( d = 19.6 Å) is present in the X-ray scattering pattern corresponding to the dry fi lm. Note that in the out-of-plane direction, this feature is found to coincide with an X-ray fl are above the beamstop.…”

Competition between substrate-mediated π-π stacking and surface-mediated Tg depression in ultrathin conjugated polymer films

“…3b was recorded from a PCDTBT film that had been subject to the same heating and cooling cycles used in the ellipsometry measurements used to determine T g . Here, a new diffraction peak at q = 0.63Å −1 appears in the out-of-plane direction of the 2D image: a feature recently assigned as the 2nd-order diffraction of the bi-layer lamella spacing [22]. Such a structure is observed if a PCDTBT film is annealed above its bulk T g and originates from PCDTBT molecules adopting a lamellar structure with an edge-on orientation [22].…”

“…The innermost diffraction ring at a q = 0.31Å −1 (partly blocked in the out-of-plane direction by the flare after the beam stop) is attributed to 1st-order scattering from sidechain ordering, and is associated with the distance (ca. 20Å) between bi-layer ordered lamella of PCDTBT backbones separated by the two alkyl side-chain lengths [13,21,22].…”

”Face-On” Oriented ^|^pi;-Conjugated Polymers Containing 1,3,4-Thiadiazole Moiety Investigated with Synchrotron GIXS Measurements: Relationship between Morphology and PSC Performance

“…In order to achieve both the processability and effective photoelectrical conversion, it is essential to understand the relationship between the device performance and morphological properties of the composite film, e.g., the degree of crystallization, domain size, polymer orientation, connectivity of each separated p/n domain, etc. Therefore, the morphology has been investigated in detail for high performance p-type polymers, such as benzothiadiazole (BT) containing polymers which are representative semiconductors showing high open-circuit voltage (V oc ) for the PSC applications [2][3][4][5][6].…”