Controlling the solid-state microstructure of organic semiconducting materials by molecular compound formation

Abstract

Controlling the thin-film nano- and microstructure of active components in org.-based electronic devices such as org. field-effect transistors, org. light-emitting diodes and org. photovoltaic devices is still a challenging but crucial task [Sirringhaus H, Brown PJ, Friend RH, Nielsen MM, Bechgaard K, Langeveld-Voss BMW, Spiering AJH, Janssen RAJ, Meijer EW, Herwig P, de Leeuw DM. Two-dimensional charge transport in self-organized, high-mobility conjugated polymers. Nature. 1999;401:685-688; Yu G, Gao J, Hummelen JC, Wudl F, Heeger AJ. Polymer photovoltaic cells: enhanced efficiencies via a network of internal donor-acceptor heterojunctions. Science. 1995;270:1789-1791; Ray B, Alam MA. Optimum morphol. and performance gains of org. solar cells. 2011 37th IEEE Photovoltaic Specialists Conference. IEEE;2011;2:003477-003481]. Over the past decade, numerous strategies have been explored for this purpose, including chem. modification of relevant materials and substrates, optimization of existing processing procedures (through selection of solvents and processing conditions, annealing procedures, etc.), as well as the development of entirely new deposition techniques [Subramanian S, Park SK, Parkin SR, Podzorov V, Jackson TN, Anthony JE. Chromophore fluorination enhances crystn. and stability of sol. anthradithiophene semiconductors. J. Am. Chem. Soc. 2008;130:2706-2707; Reese C, Roberts M, Ling M, Bao Z. Org. thin film transistors. Mater. Today. 2004;7:20-27; Halik M, Klauk H, Zschieschang U, Maisch S, Effenberger F, Dehm C, Schu M, Brunnbauer M, Stellacci F. Low-voltage org. transistors with an amorphous mol. gate dielec. Nature. 2004;431:963-966; Kim CS, Lee S, Gomez ED, Anthony JE, Loo YL. Solvent-dependent elec. characteristics and stability of org. thin-film transistors with drop cast bis(triisopropylsilylethynyl) pentacene. Appl. Phys. Lett. 2008;93:103302-103304; Dickey KC, Anthony JE, Loo YL. Improving org. thin-film transistor performance through solvent-vapor annealing of soln.-processable triethylsilylethynyl anthradithiophene. Adv. Mater. 2006;18:1721-1726; Street RA. Thin-film transistors. Adv. Mater. 2009;21:2007-2022; de Gans BJ, Duineveld PC, Schubert US. Inkjet printing of polymers: state of the art and future developments. Adv. Mater. 2004. Additives have thereby been shown to provide extra means to significantly influence the mol. assembly and order in the solid state of the active species [Peet J, Kim JY, Coates NE, Ma WL, Moses D, Heeger AJ, Bazan GC. Efficiency enhancement in low-bandgap polymer solar cells by processing with alkane dithiols. Nat. Mater. 2007;6:497-500; Wei Q, Lin Y, Anderson ER, Briseno AL, Gido SP, Watkins JJ. Additive-driven assembly of block copolymer-nanoparticle hybrid materials for soln. processable floating gate memory. ACS Nano. 2012;6:1188-1194]. Here, we will discuss the use of a class of additives that can form mol. compds. with the active materials, adding to the extensive tool box for microstructural control because cryst. solid-state structures can be realized where chromophores are spatially sepd. from each other by the additive mols. without compromising the overall long-range order of the system. [on SciFinder(R)]