Temperature-Dependent Evolution of Poly(3-Hexylthiophene) Type-II Phase in a Blended Thin Film

Abstract

The structure of P3HT in P3HT:PCBM films is examined on a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) substrate subjected to cryo-cooling to low temperature (-143 degrees C) followed by gradual heating to 50 degrees C. The behavior of these systems is examined in the absence and presence of an Al electrode on top of the P3HT:PCBM film. At temperatures below -10 degrees C, only the type-I phase of P3HT is observed. However, the type-II phase of P3HT starts to form near -10 degrees C, in both the presence and absence of the Al layer. In the system without an Al layer, the type-II phase disappears at 30 degrees C, but this phase persists to 50 degrees C in the presence of the Al layer. Concomitant with the formation of the type-II phase, a 1:3 ordered P3HT type-II (1/3,0,0) superlattice peak emerged. The type-II domains tend to form near the Al electrode layer and show a higher degree of alignment than the type-I crystals.