Toward n-type analogues to poly(3-alkylthiophene)s: influence of side-chain variation on bulk-morphology and electron transport characteristics of head-to-tail regioregular poly(4-alkylthiazole)s

Series of three new highly head-to-tail regioregular poly(4-alkylthiazole)s (PTzTIB, PTzTNB, and PTzTHX) equipped with different trialkylsilyloxymethyl (R3SiOCH2-) side-chains have been prepared (PTzTIB: R = isobutyl, PTzTNB: R = n-butyl, PTzTHX: R = n-hexyl). The polymers exhibit very similar optical and electronic properties, in agreement with the isoelectronic nature of their respective conjugated systems. However, bulk properties, such as (in) solubility, melting behavior and solid-state morphology are strongly affected by the nature of the side-chains. PTzTHX in particular can be readily crystallized through annealing, and exhibits a remarkable tendency to self-organize into crystalline lamellae, that are 50-100 nm wide, and up to 10 mu m in length, as demonstrated by investigation of polymer films via GIXD, and AFM and SEM-imaging. Electrical characterization of PTzTNB and PTzTHX in hole-only-and electron-only devices show electron mobilities to be consistently higher than hole mobilities with maximum mobilities of mu(e) = 6.4 x 10(-4) cm(2) V-1 s(-1) observed for PTzTHX and mu(e) = 2.7 x 10(-4) cm(2) V-1 s(-1) for PTzTNB. PTzTHX outperforms the less crystalline PTzTNB despite the higher bulk of insulating side-chains. Furthermore, electron-mobilities of PTzTHX are shown to correlate both with the molecular weight and the crystallization after annealing.