P3HT/PCBM photoactive materials for solar cells: Morphology and dynamics by means of solid-state NMR

Abstract

P3HT/PCBM blends before and after annealing at 150 C, as well as the corresponding neat materials have been deeply investigated by means of a multinuclear and multitechnique solid-state NMR approach. 13C CP/MAS spectra, high-resolution 1H T1 measurements and low-resolution 1H FID analysis allowed us to obtain information on the phase and morphological properties on a nanometric and subnanometric scale of both the blends and the neat materials. Variable-temperature 1H and 13C T1 measurements have been carried out and the experimental relaxation times have been analyzed using sophisticated models to obtain a detailed characterization of the dynamic behavior of P3HT in the MHz frequency range in both the blends and the neat polymer. The results obtained highlighted a decrease of mobility of the side chains in passing from P3HT to the blend before annealing, probably due to the intimate mixing with PCBM, and an increase of phase separation between P3HT and PCBM after annealing, correlated with an increase of free volume, and therefore to the observed increase of mobility of the alkylic side-chains. © 2012 American Chemical Society.