Role of Solution Structure in Self-Assembly of Conjugated Block Copolymer Thin Films

Abstract

Conjugated block copolymers provide a pathway to achieve thermally stable nanostructured thin films for organic solar cells. We characterized the structural evolution of poly(3-hexylthiophene)-block-poly(diketopyrrolopyrrole-terthiophene) (P3HT-b-DPPT-T) from solution to nanostructured thin films. Aggregation of the DPPT-T block of P3HT-b-DPPT-T was found in solution by small angle X-ray scattering with the P3HT block remaining well-solvated.The nanostructure in thin films was determined using a combination of wide and small angle Xray scattering techniques as a function of processing conditions. The solution structure controlled the initial nanostructure in spin-cast thin films allowing subsequent thermal annealing processes to further improve the ordering. In contrast to the results for thin films, nanostructural ordering was not observed in the bulk samples by small angle X-ray scattering. These results suggest the importance of controlling solvent induced aggregation in forming nanostructured thin films of conjugated block co-polymers.

Understanding Solution State Conformation and Aggregate Structure of Conjugated Polymers via Small Angle X-ray Scattering

“…Liu and Boué et al 20 similarly used a parallelepiped and cylinder model to analyze SANS of DPPDTT finding the D-A polymer conformation to transition from rod-like chains in good solvents to ribbon-like aggregates and networks in poor solvents. While these works have successfully modeled and analyzed D-A polymer scattering, they have not observed the high 𝑞 structure factor peak that has been reported in several other studies [21][22][23] and observed consistently in our work.…”

“…In doing so, we are not only able to fit and extract structural parameters from scattering but also establish the physical basis for the unique features observed in D-A polymer scattering and thereby improve the understanding of conjugated polymer solution state aggregation. In particular, we resolve the origin of the broad high 𝑞 peak that has been intermittently reported in prior works [21][22][23] . While it has been speculated to be due to lamellar stacking it has not been clearly explained or modeled so far.…”

“…First, at low 𝑞 (𝑞 < 0.02 Å −1 ) a power law of ~−1.2 to −1.6 is observed instead of an overall Guinier region preceded by constant flat intensity indicating that the PII-2T chains are not dispersed but are aggregating into a larger structure. Such low 𝑞 power law scattering and even steeper is commonly observed in small angle scattering of conjugated polymers [11][12][13][14]21,22 . Given the known tendency of PII-2T to form nanofibrils 31 a slope of −1.2 to −1.6 at this length scale is expected, corresponding to a large semiflexible object in between that of a rigid rod (−1) and random coil (−2).…”

Photophysical and Optical Properties of Semiconducting Polymer Nanoparticles Prepared from Hyaluronic Acid and Polysorbate 80

“…Overall, the measured TA spectra for all polymers before nanoprecipitation are similar to those which have been previously reported for other π-conjugated DPP-based polymers. 53 The UV spectral window (350–590 nm) revealed a ground-state bleach signal corresponding to the high energy absorption band (Figure 3) assigned to the aromatic thiophene units. A small photoinduced absorption signal can also be observed, which can be assigned to the S 0 → S n absorption of the thiophene units.…”

Aluminum oxide free-standing thin films to enable nitrogen edge soft x-ray scattering

“…[7,13] Despite the opportunity to examine the distribution of nitrogen (N) in organic and biological compounds, very few studies have employed RSoXS at the N edge. [14] The challenge lies in the x-ray transparent support, which is 50-100 nm thick Si 3 N 4 that produces a significant RSoXS background at energies near the N edge. These Si 3 N 4 supports are formed through a lowpressure chemical vapor deposition (LPCVD) process and have Young's moduli between 140 and 290 GPa [15] with a fracture toughness of about 6 MPa•m 0.5 .…”