Inhomogeneity of spin-coated and cast non-regioregular poly(3-hexylthiophene) films. Structures and electrical and photophysical properties

We report structures and electrical and photophysical properties of spin-coated and cast non-regioregular poly(3-hexylthiophene) (P3HT) films. Large differences of the properties are found in these films prepared from different conditions. Results of optical absorption, electron spin resonance, and X-ray diffraction measurements show that the extent of conjugation of P3HT is homogeneous in the spin-coated film, whereas it is inhomogeneous in the cast film. The existence of relatively strong distorted segments with large torsion angles in the thiophene backbone is also suggested, especially in the cast film. Carrier transfer phenomena and unrelaxed exciton diffusion to an emissive singlet polaron exciton are discussed on the basis of proposed structure models of the spin-coated and the cast films.