Spectral Signatures and Spatial Coherence of Bound and Unbound Polarons in Organic Semiconductors: Theory vs Experiment*

The spectral line-shape of the mid-IR absorption spectrum provides valuable information about the “hole” polaron coherence length in doped and undoped conjugated polymer films. Using a theory based on the Holstein Hamiltonian for mobile holes in P3HT, the IR line-shape is successfully reproduced for several recently measured spectra recorded in doped and undoped films, confirming the association of an enhanced peak ratio (A/B) with extended polaron coherence. Emphasis is placed on the origin of components polarized along the intra- and inter-chain directions and their dependence on the spatial distribution of disorder and the position of the dopant relative to the π-stack. The model has been further adapted to treat donor-acceptor copolymers.

References:
1. Raja Ghosh, Christine K Luscombe, Mike Hambsch, Stefan CB Mannsfeld, Alberto Salleo, and Frank C Spano. Anisotropic polaron delocalization in conjugated homopolymers and donor–acceptor copolymers. Chemistry of Materials, 2019
2. Raja Ghosh, Annabel R. Chew, Jonathan Onorato, Viktoria Pakhnyuk, Christine K. Luscombe, Alberto Salleo, and Frank C. Spano. Spectral 138 signatures and spatial coherence of bound and unbound polarons in p3ht films: Theory versus experiment. J. Phys. Chem. C, 122(31):18048– 18060, 2018.