Morphological and spectroscopic characterizations of inkjet-printed poly(3-hexylthiophene-2,5-diyl): Phenyl-C61-butyric acid methyl ester blends for organic solar cell applications

Abstract

The most exploited active material for photovoltaic devices is the regioregular poly(3-hexylthiophene) (P3HT), p-type conjugated polymer, blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), n-type material. The deposition methods and the induced morphology strongly influence the functionality of the active material and in turn the final charge generation performances of a photoactive layer.In the present work, we studied the influence of PCBM concentration on the morphological and spectroscopic properties of the inkjet printed P3HT:PCBM blends through atomic force microscopy (AFM), Raman spectroscopy and transient absorption spectroscopy. The aim is to value the charge formation yield in the blends, prepared by inkjet technology, as function of the acceptor concentrations in correlation with morphology and intermixing of the two components. For the inkjet printed samples the blends composition that corresponds to the best intermixing between P3HT and PCBM and the higher charges formation yield should be between 20% and 45% in weight (wt)., differently for what has been found previously for spin-coated samples. Indeed, for inkjet prepared film, the 45wt.% blend ratio leads to much bigger domains with respect to the spin-coated samples as shown from the AFM measurements.