A Self‐Doping, O₂‐Stable, n‐Type Interfacial Layer for Organic Electronics

Abstract

Solid fi lms of a water-soluble dicationic perylene diimide salt, perylene bis(2ethyltrimethylammonium hydroxide imide), Petma + OH − , are strongly doped n-type by dehydration and reversibly de-doped by hydration. The hydrated fi lms consist almost entirely of the neutral perylene diimide, PDI, while the dehydrated fi lms contain ∼ 50% PDI anions. The conductivity increases by fi ve orders of magnitude upon dehydration, probably limited by fi lm roughness, while the work function decreases by 0.74 V, consistent with an n-type doping density increase of ∼ 12 orders of magnitude. Remarkably, the PDI anions are stable in dry air up to 120 ° C. The work function of the doped fi lm, ϕ (3.96 V vs. vacuum), is unusually negative for an O 2 -stable contact. Petma + OH − is also characterized as an interfacial layer, IFL, in two different types of organic photovoltaic cells. Results are comparable to state of the art cesium carbonate IFLs, but may improve if fi lm morphology can be better controlled. The fi lms are stable and reversible over many months in air and light. The mechanism of this unusual self-doping process may involve the change in relative potentials of the ions in the fi lm caused by their deshielding and compaction as water is removed, leading to charge transfer when dry. 456 www.MaterialsViews.com www.advenergymat.de

Review—Organic Materials for Thermoelectric Energy Generation

“…86 Efficient n-type doping has been achieved by the addition of pendant trimethyl amine groups to molecular perylene-diimide derivatives, 81 Gregg et al reported a reversible self-doping mechanism of a water soluble PDI derivative through low temperature treatment and conductivities up to 10 −3 S.cm −1 achieved. 84 Segalman and co-workers recently presented that self-doped PDIs have one of the highest n -type thermoelectric performance of solution-processed organic materials reported so far. 82 They reported PDI derivatives with various chain lengths that are strongly correlated to the morphology and electronic properties.…”

“…Chabinyc and Segalman and others recently demonstrated the introduction of extrinsic dopants that localizes the dopants within the active host matrix and create high electrical conductivity and thermoelectric performance. [81][82][83][84] Recently, perlyenediimides (PDIs) emerged as solution processable organic semiconductors that have high EA (∼4.0 eV) where the structural modifications enable to tune the energetic levels. 85 Chemical modifications of the PDI core can deliver water soluble derivatives enabling a pathway toward non-toxic, solution processing of thin films.…”

Application of a water-soluble metallophthalocyanine derivative as a cathode interlayer for the polymer solar cells

“…Compared to other cathode interfacial layer materials, advantages of alcohol/water-soluble organic materials are apparent in the PSCs due to their simple, vacuum-free and environment-friendly procedure to form film during the device fabrication and universality for different active layer and different metal cathode [22,23]. So far reported CILs improving the device performance mainly consist of polymers [24][25][26][27][28][29][30][31][32][33][34] and organic small molecules [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49]. Compared to polymers, organic small molecules are more attractive because of their several intrinsic advantages over the conjugated polymer counterpart in terms of easy purification, monodispersity and well-defined structures without end group contaminants and better batch-to-batch reproducibility.…”

“…Compared to polymers, organic small molecules are more attractive because of their several intrinsic advantages over the conjugated polymer counterpart in terms of easy purification, monodispersity and well-defined structures without end group contaminants and better batch-to-batch reproducibility. Successful alcohol/water soluble small molecular CIL materials include fullerene derivatives [35][36][37][38][39], perylene diimides [40,41], porphyrin [42], pyridinium salt [43], rhodamine with inner salt [44], quinacridone tethered with sodium sulfonate [45], triphenylamine-uorene core featuring a phosphonate side chain [46], tetra-n-alkyl ammonium bromides [47], and metallophthalocyanine (MPc) derivative [48,49].…”

Synthesis of tetracationic organic salt from 4,4'-bipyridine

“…This is due to the potential to change their structural features simply by: varying the nature of the cation and/or the anion; tuning them by introducing small structural changes in the constituting ions, or of the spacers separating them provides the opportunity to obtain materials with sets of desired properties suitable for different applications. They have been applied as a chemical anchorage on a solid support [10], starting materials for the synthesis of molecular devices [11,12], reaction media or catalysts, immobilization of catalysts [9], reaction media for high-temperature organic reactions [13,14], catalysts [15], receptors for anion recognition [16], low-molecular-weight gelators [17], fluorescent organic salts [18,19], energetic materials [20,21], for use in the preparation of solid films for organic electronic applications [22] and electrowetting materials [23]. Heteromolecules including imidazole, 1,10-phenanthroline, pyridine and others have been used as the starting materials for the synthesis of polycationic organic salts.…”