Strong polymer molecular weight-dependent material interactions: impact on the formation of the polymer/fullerene bulk heterojunction morphology

Abstract

The morphological evolution is initiated by L–L or L–S phase separation (left) and further developed by molecular mobility, governed by polymer–solvent interactions which determine the final domain size of the BHJ layer (right).

The Critical Impact of Material and Process Compatibility on the Active Layer Morphology and Performance of Organic Ternary Solar Cells

“…DPP-LBGP and J40 have shown unfavorable interactions denoted by a large interaction parameter, χ PP of 0.384 (Table S5, Supporting Information) and incomplete miscibility from DSC results ( Figure S7, Supporting Information). [54] and [39], respectively. While one may expect that this thermodynamic driving force leads to liquid-liquid demixing to produce highly pure globular domains of which the purity is given by the binodal of the phase diagram ( Figure S11 a) The solubility of the pristine polymers and PC 71 BM was measured by dissolving the materials in TMB and DIO over the solubility limit and estimated by using Beer-Lambert law: A = cLε, where A is absorbance, c is concentration (solubility), L is reciprocal length, and ε is molar absorption coefficient.…”

“…However, at a fraction of DPP-LBGP larger than 40%, no polymer fibers are discernible ( Figure 3). [39,48,49] This measurement provides information about degree of ordering (DoO) which is estimated by integrating (100) lamellar crystalline peak through q ranges and normalizing by polymer volume fraction to compare crystalline ordering of two polymers and coherence length of (100) lamellar peak both in the out-of-plane (OOP) and in-plane (IP) directions (Figure 4b,c and Table 2). Indeed, the root-mean square roughness decreases (i.e., the films become smoother) upon decreasing J40 content in the DPP-LBGP:J40 mixture ( Figure 3).…”

“…This reduced solubility of DPP-LBGP is manifested in the larger value of its polymer-solvent interaction parameter χ 12 (Table S5, Supporting Information). [38,39] Because the polymer-polymer interaction parameter is χ PP ≈ 0.384, this implies there is a driving force for phase separation between the two polymers at a volume fraction as low as 0.8%. These values (which, in the following, we presumed to be independent of the presence of DIO) are sufficiently large to provide a driving force for phase separation between both polymers and the fullerene.…”

“…[23][24][25][26][27][28][29][30][31] Those TSCs have to overcome material incompatibility and processing problems, which create a major bottleneck in obtaining the desirable ternary blend nanomorphologies. [37][38][39] On the other hand, compatible processing requires that the best solvent processing conditions of the binary blends are very similar if not identical, a condition rarely met. [37][38][39] On the other hand, compatible processing requires that the best solvent processing conditions of the binary blends are very similar if not identical, a condition rarely met.…”

“…[37][38][39] On the other hand, compatible processing requires that the best solvent processing conditions of the binary blends are very similar if not identical, a condition rarely met. [37][38][39] In particular, the difference in solubility between the two polymers implies a different timescale at which their solubility limit is reached. [40][41][42][43][44][45] Therefore, understanding the key factors controlling the ternary morphology will guide the design of highly efficient and stable TSCs.…”