Unraveling the Molar Mass Dependence of Shearing‐Induced Aggregation Structure of a High‐Mobility Polymer Semiconductor

Abstract

Aggregation‐structure formation of conjugated polymers is a fundamental problem in the field of organic electronics and remains poorly understood. Herein, the molar mass dependence of the aggregation structure of a high‐mobility conjugated copolymer (TDPP‐Se) comprising thiophene‐flanked diketopyrrolopyrrole and selenophene is thoroughly shown. Five batches of TDPP‐Se are prepared with the number‐average molecular weights (Mn) varied greatly from 21 to 135 kg mol−1. Small‐angle neutron scattering and transmission electron microscopy are combined to probe the solution structure of these polymers, consistently using a deuterated solvent. All the polymers adopt 1D rod‐like aggregation structures and the radius of the 1D rods is not sensitive to the Mn, while the length increases monotonically with Mn. By utilizing the ordered packing of the aggregated structure in solution, a highly aligned and ordered film is prepared and, thereafter, a reliable hole mobility of 13.8 cm2 V−1 s−1 is realized in organic thin‐film transistors with the moderate Mn batch via bar coating. The hole mobility is among the highest values reported for diketopyrrolopyrrole‐based polymers. This work paves the way to visualize the real aggregated structure of polymer semiconductors in solution and sheds light on the microstructure control of high‐performance electronic devices.

Aggregation Behavior and Electrical Performance Control of Isoindigo-Based Conjugated Polymers via Carbosilane Side Chain Engineering

“…As shown in Figure b, we infer that with the increase of bulkiness and steric hindrance from C 12 , SiC 12 to SiC 8 , the assembly of resulting polymer molecules is hampered and the number of molecule chains is reduced, resulting in gradually decreased radius of 1D fibrillar pre-aggregates in solution. The relationship between the length of pre-aggregates and OTFT performance has been detailed previously . As the length of pre-aggregates does not change significantly in the current work, we thus focus on discussing the role of other shape factors of pre-aggregates, that is, radius and aspect ratio.…”

“…The relationship between the length of pre-aggregates and OTFT performance has been detailed previously. 24 As the length of pre-aggregates does not change significantly in the current work, we thus focus on discussing the role of other shape factors of pre-aggregates, that is, radius and aspect ratio. The aspect ratio of pre-aggregates was calculated by the ratio of the contour length over radius of the aggregates, and so, these two factors actually determined the aspect ratio.…”

“…Comparative studies confirmed that a favorable branch point position determined the formation of the alignable anisotropic precursor in solution and was critical for improved electrical performance. Other reports have also clarified that the film microstructure order of semicrystalline CPs was largely inherited from the molecular packing in solution. − Although the side chain strategy has been intensively discussed, there is still a lack of in-depth understanding of how the growth of molecules to solution pre-aggregates then to solid aggregates is related to the subtle side chain modification. It is actually rather difficult to investigate these structure-property relationships by adjusting the structure of alkyl side chains due to their synthetic complexity and high cost.…”

“…A series of IID-based CPs, namely IIDC 12 , IIDSiC 12 , and IIDSiC 8 with branched alkyl 7-dodecylnonadecyl, moderately bulky 6-(didodecyl­(methyl)­silyl) hexyl and voluminous 6-(trioctylsilyl) hexyl carbosilane side chains, respectively, were synthesized by direct arylation polymerization (DArP). − We demonstrated that with a constant branching point position, the flexibility and bulkiness of the side chains dictated the solution behavior of the polymers, thereby significantly influencing the molecular packing order in thin film via bar coating processing. As evidenced by solution small-angle neutron scattering (SANS) and transmission electron microscopy (TEM), ,− all three polymers formed one-dimensional rod-like aggregates but with different sizes and aspect ratios in o -DCB. Less flexible and bulky alkyl chains imposed a shorter and thicker manner dimension on IIDC 12 , while thinner objects with larger aspect ratios were observed for IIDSiC 12 and IIDSiC 8 .…”

Unraveling the Photovoltaic, Mechanical, and Microstructural Properties and Their Correlations in Simple Poly(3‐pentylthiophene) Solar Cells

“…Note that AFM and TEM are not capable of visualizing the inner structure and vertical gradient. Due to the lack of more advanced characterization tools, [53,62] precise determination of the inner structure is outside the scope of this study.…”