Lamellar and liquid crystal ordering in solvent-annealed all-conjugated block copolymers

Abstract

All-conjugated block copolymers are an emerging class of polymeric materials promising for organic electronic applications, but further progress requires a better understanding of their microstructure including crystallinity and self-assembly through micro-phase segregation. Here, we demonstrate remarkable changes in the thin film structure of a model series of all-conjugated block copolymers with varying processing conditions. Under thermal annealing, poly(3-hexylthiophene)-b-poly(9',9'-dioctylfluorene) (P3HT-b-PF) all-conjugated block copolymers exhibit crystalline features of P3HT or PF, depending on the block ratio, and poor π-π stacking. Under chloroform solvent annealing, the block copolymers exhibit lamellar ordering, as evidenced by multiple reflections in grazing incidence wide- and small-angle X-ray scattering (GIWAXS and GISAXS), including an in-plane reflection indicative of order along the π-π stacking direction for both P3HT and PF blocks. The lamellae have a characteristic domain size of 4.2 nm, and this domain size is found to be independent of block copolymer molecular weight and block ratio. This suggests that lamellar self-assembly arises due to a combination of polymer block segregation and π-π stacking of both P3HT and PF polymer blocks. Strategies for predicting the microstructure of all-conjugated block copolymers must take into account intermolecular π-π stacking and liquid crystalline interactions not typically found in flexible coil block copolymers.

Critical Role of Polymer Aggregation and Miscibility in Nonfullerene‐Based Organic Photovoltaics

“…It should be noted that semicrystalline polymers typically organize into lamellar crystalline domains, having a face-to-face π-π stacking between backbones and lamellar stacking through the side chains. [35] Here, the pristine T4T and T3T polymers show well-defined lamellar peaks (100) at 0.28 Å −1 and π-π stacking peaks (010) at 1.78 Å −1 (Figure S8, Supporting Information). The intensities of the higher ordered peaks, (200) and (300), gradually decrease as the T3T units increase, indicating a reduction in long-range molecular order.…”

“…To understand why tuning the ratio between T4T and T3T in these polymers causes a dramatic difference in exciton dynamics, we investigate how the aggregation properties of the donor polymer influence molecular packing in the blends using grazing incidence wide angle X‐ray scattering (GIWAXS). It should be noted that semicrystalline polymers typically organize into lamellar crystalline domains, having a face‐to‐face π–π stacking between backbones and lamellar stacking through the side chains . Here, the pristine T4T and T3T polymers show well‐defined lamellar peaks (100) at 0.28 Å −1 and π–π stacking peaks (010) at 1.78 Å −1 (Figure S8, Supporting Information).…”

Semiconducting alternating multi-block copolymers via a di-functionalized macromonomer approach

“…[9][10][11][12][13] These polymers have demonstrated impressive self-assembly into nanoscale phase domains 9,10,14 and have indeed been demonstrated as promising materials for use in OPVs. [15][16][17][18] However, in the majority of these examples poly(3-alkylthiophene), most commonly the hexyl derivative, P3HT, 19 is used for one of the blocks. Indeed, strategies thus far have primarily employed regio-regular P3HT prepared via a nickel-mediated cross-coupling route (McCullough and GRIM methods).…”

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

“…This goal has been met by BCPs where either one block has a conjugated backbone and the other has an insulating backbone with pendant conjugated molecules, [29][30][31][32][33][34][35][36][37] or by structures where both blocks have conjugated backbones (CBCPs). [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] Because of the relative stiffness of conjugated backbones, the phase separation of their BCP is complex due to energetic interactions between blocks, the volume fraction of the blocks, and potential crystallization.…”