Thermal and Structural Characteristics of Oligo(3-hexylthiophene)s (3HT)_n, n = 4–36

Abstract

This study is concerned with the thermal and structural characteristics of a series of precisely defined, monodisperse, regioregular oligo(3-hexylthiophene)s (3HT)n of n = 4-36. We find that these model compounds can feature two distinctly different solid-state structures, i.e., the more classical polymorph Form I in which the hexyl side-chains are not interdigitated and Form II in which they are. The thermodynamic equilibrium melting temperatures of these phases differ as much as ~180 °C, with 116 °C for Form II and 298 °C for Form I. Furthermore, polymorph II featured an enthalpy of melting of ~3 times that of Form I and a rate of crystallization that is ~1 order of magnitude lower than that of Form I. A crossover of the thermodynamically preferred Form II into the kinetically favored Form I is observed at a number of repeat units of 12. In the regime 10 ≤ n ≤ 21 the oligo(3-hexylthiophene)s could readily be reversibly converted from one polymorph to another by appropriate processing treatments. The relevance of these findings for the polymeric form (P3HT) is discussed.

Mechanical degradation and stability of organic solar cells: molecular and microstructural determinants

“…75 The side chains of the P3ATs generally do not interdigitate, 75 and thus the lamellae within the crystallites should not be as highly registered vertically as in materials in which the side chains do interdigitate (such as PBTTT 33,66 and PT2T 97 ). 75 The side chains of the P3ATs generally do not interdigitate, 75 and thus the lamellae within the crystallites should not be as highly registered vertically as in materials in which the side chains do interdigitate (such as PBTTT 33,66 and PT2T 97 ).…”

“…33 As-cast samples of PBTTT, which have small crystallites, 66 exhibited tensile moduli that were half those of annealed lms, 33 which exhibited large crystallites (and low amorphous fractions) in an earlier study by AFM. 75 For example, the crystalline domains of P3ATs have two known packing structures. 33 PT2T (Fig.…”

“…33 PT2T (Fig. Form II occurs in oligomers of 3-hexylthiophene, 75 and for both P3BT and P3HT, conversion from Form I to Form II can occur by exposure to certain solvent vapors (e.g., carbon disulde). 97 Interestingly, the tensile modulus of PT2T was similar to that of P3HT when cast under similar conditions.…”

Origin of fullerene-induced vitrification of fullerene:donor polymer photovoltaic blends and its impact on solar cell performance

“…Since the oen quoted value of the enthalpy of fusion of rr-P3HT (DH c ) of 16 kJ mol À1 reported by Malik et al 30 has recently been challenged to be about a factor two lower, 33,36,37 typically leads to a higher absolute value for c P3HT-ICBA (c P3HT-ICBA ¼ 0.3), while the other parameters remain more or less unchanged. As we will see, a lower value for DH c leads to a more pronounced thermodynamic contribution to the melting point depression, as it appears in the denominator in the RHS of eqn (2).…”

Selective Nucleation of Poly(3-hexyl thiophene) Nanofibers on Multilayer Graphene Substrates

“…Similarly, atomic force microscopy (AFM) and optical profilometry measurements reveal a slow increase in the average film thickness with time, up to 5.4 ± 0.8 nm after 120 h of incubation. Assuming a density of 1.1 g/mL for P3HT, 24 these thicknesses can be compared to the UV−vis spectra ( Figure S3a, Supporting Information) to determine an absorption coefficient at 602 nm for the solid films (ε s ). Interestingly, the value of ε s = 270 ± 30 mL cm −1 mg −1 is more than an order of magnitude larger than the value of ε f for the suspended NFs.…”