Molecular Gates: Unlocking the Path to High-Resolution Patterning of Doping, Orientation and Microstructure in Organic Semiconductors Films

Miniaturization of silicon devices that underpinned the electronics revolution was largely enabled by developments in photolithography-based patterning. The field of molecular electronics requires a similar versatile means of patterning key material characteristics of organic semiconductors films that is compatible with the optimal high-throughput solution-based fabrication schemes. For instance, local doping is a principal requirement for the fabrication of organic field-effect transistors (OFETs) and thermoelectric generators (OTEGs).[1] The patterning of (macro-)molecular orientation can unlock dramatic device performance enhancements—often by an order of magnitude of more—as well enable unique functionalities in the fields of security and photodetection.[2] Microstructure and molecular conformation are yet another parameter space for which local patterning is sought for the design of integrated photonic components and waveguides.[3] The state-of-the-art methods, however, exhibit major drawbacks, e.g. the compromise between resolution and throughput, restrictive vacuum requirements or limited generality.[4,5] A further disadvantage is the absence of a patterning platform that can simultaneously address all pattern types.<br/><br/>We present a versatile concept, wherein a solution-deposited semipermeable ‘molecular gate’ interlayer is used to separate an organic semiconductor film and an overlayer comprising functional small-molecular additives.[6] The molecular gate modulates diffusion of additives into the organic semiconductor film with a ‘molecule-on-demand’ precision. Additive diffusion is stimulated locally by laser light, heat or solvent vapor. By selection of functional compounds, we demonstrate patterning of electrical doping, chain orientation, and material composition in benchmark semiconducting polymers with near-photolithographic resolution and speeds in the mm s^–1 range.<br/><br/>In particular, we report laser-based fabrication of 10-μm-wide patterns of p-doping in PBTTT with local conductivities reaching 10 S cm^–1, and describe a general analytical approach based on spectroscopic Raman mapping to accurately quantify the degree of doping within μm-scale patterns. Furthermore, we advance the novel use of solid co-solvents as processing aids for increasing throughput and reducing processing temperatures. Exemplary patterning of directional chain orientation is demonstrated for P3HT with &lt;5 μm resolution to enable anisotropic electronic and heat transport. Finally, we illustrate the unique capability of the method for <i>one-step</i> patterning of <i>multiple</i> functionalities by spatially modulating sensitizer composition and excitation energy transfer in ternary blends, enabling on-demand broadband photoluminescence tuning from 420 to 620 nm.<br/><br/>Emphasis is placed throughout on broad adaptability of molecular-gate-based patterning to conventional materials processing methods such as spin-, spray- and slot-die coating, as well as inkjet printing, to realize application concepts in electronics and optics. Given the generality of the underlying principles and a plurality of suitable additives, the presented method can bridge the gap between high-resolution laboratory-scale processing and high-throughput industrial fabrication of patterned organic semiconductor devices.<br/><br/>[1] Y. Xu <i>et al</i>., <i>Adv. Mater</i>. <b>2018</b>, <i>30</i>, 1801830; [2] D. Khim <i>et al</i>., <i>Adv. Mater</i>. <b>2018</b>, <i>30</i>, 1705463; [3] A. Perevedentsev <i>et al</i>., <i>Nat. Commun</i>. <b>2015</b>, <i>6</i>, 5977; [4] B. E. Kahn, <i>Proc. IEEE</i> <b>2015</b>, <i>103</i>, 497; [5] I. E. Jacobs <i>et al.</i>, <i>ACS Nano</i> <b>2021</b>, <i>15</i>, 7006; [6] A. Perevedentsev <i>et al</i>., <i>Nat. Commun</i>. <b>2020</b>, <i>11</i>, 3610.