Salts of cyclopentadiene as n-dopants for organic electronics

Abstract

An organic electron transport layer has at least one dopant for increasing the n-conductivity of the organic layer. The dopant is selected from the group of salts of cyclopentadiene compounds according to formula 1, wherein the substituents R1 to R2 are independently selected from the group containing H, -D, halogen, CN, NO2, OH, amine, ether, thioether, alkyl, cycloalkyl, acrylic, vinyl, allyl, aromatics, fused aromatics and heteroaromatics.

Claims

1. An organic electron-conducting layer, comprising: at least one dopant to increase the n-conductivity of the organic electron-conducting layer, wherein the at least one dopant is selected from the group consisting of salts of cyclopentadiene compounds of the following formula: ##STR00004## where M.sup.+ is an alkali metal, and the substituents R.sub.1 to R.sub.5 are each independently selected from the group consisting of H, deuterium, halogens, CN, NO.sub.2, OH, amines, ethers, thioethers, alkyls, cycloalkyls, acryloyls, vinyls, allyls, aromatics, fused aromatics and heteroaromatics, and the salts of the cyclopentadiene compounds have sublimation temperatures that are greater than or equal to 120? C. and less than or equal to 600? C.

2. The organic electron-conducting layer as claimed in claim 1, wherein the at least one dopant is selected from the group consisting of unsubstituted and substituted pentaarylcyclopentadiene salts.

3. The organic electron-conducting layer as claimed in claim 1, wherein M.sup.+ is an alkali metal cation selected from the group consisting of lithium, sodium, potassium, rubidium and cesium.

4. The organic electron-conducting layer as claimed in claim 1, wherein M.sup.+ is a heavy alkali metal cation selected from the group consisting of rubidium and cesium.

5. The organic electron-conducting layer as claimed in claim 1, wherein an organic portion of the at least one dopant has an oxidation number of greater than or equal to ?1 and less than or equal to 0.

6. The organic electron-conducting layer as claimed in claim 1, wherein the organic electron-conducting layer is applicable to an organic electronic component by a solvent or sublimation process.

7. The organic electron-conducting layer as claimed in claim 1, wherein a molecular weight of the salts of the cyclopentadiene compounds is greater than or equal to 175 g/mol and less than or equal to 2000 g/mol.

8. The organic electron-conducting layer as claimed in claim 1, wherein the at least one dopant is present in the organic electron-conducting layer in a layer thickness concentration of greater than or equal to 0.01% and less than or equal to 50%.

9. An organic electron-conducting layer, comprising: at least one dopant to increase the n-conductivity of the organic electron-conducting layer, wherein the at least one dopant is selected from the group consisting of salts of cyclopentadiene compounds of the following formula: ##STR00005## wherein: M.sup.+ is an alkali metal; the substituents R.sub.1 to R.sub.5 are each independently selected from the group consisting of H, deuterium, halogens, CN, ?NO.sub.2, OH, amines, ethers, thioethers, alkyls, cycloalkyls, acryloyls, vinyls, allyls, aromatics, fused aromatics and heteroaromatics; and the at least one dopant is present in the organic electron-conducting layer in a layer thickness concentration of greater than or equal to 0.01% and less than or equal to 50%.

10. An organic electron-conducting layer, comprising: at least one dopant to increase the n-conductivity of the organic electron-conducting layer, wherein the at least one dopant is selected from the group consisting of salts of cyclopentadiene compounds of the following formula: ##STR00006## M.sup.+ is an alkali metal; the substituents R.sub.1 to R.sub.5 are each independently selected from the group consisting of H, deuterium, halogens, CN, NO.sub.2, OH, amines, ethers, thioethers, alkyls, cycloalkyls, acryloyls, vinyls, allyls, aromatics, fused aromatics and heteroaromatics; and the at least one dopant is present in the organic electron-conducting layer in a layer thickness concentration of greater than or equal to 1.0% and less than or equal to 10%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other objects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which:

(2) FIG. 1 shows a schematic of the structure of an organic light-emitting diode (10). The light-emitting diode is formed from a glass layer (1); indium tin oxide (ITO) layer (2); hole injector layer (3); hole transport layer (HTL) (4); emitter layer (EML) (5); hole blocker layer (HBL) (6); electron transport layer (ETL) (7); electron injector layer (8) and a cathode layer (9);

(3) FIG. 2 shows a schematic of the structure of an organic solar cell having PIN structure (20), which converts light (21) to electrical current. The solar cell includes a layer of indium tin oxide (22); a p-doped layer (23); an absorption layer (24); an n-doped layer (25) and a metal layer (26);

(4) FIG. 3 shows a schematic of a possible cross section through an organic field-effect transistor (30). Applied to a substrate (31) are a gate electrode (32), a gate dielectric (33), a source and drain contact (34+35) and an organic semiconductor (36). The hatched areas show the areas where contact doping is helpful.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(5) Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.

EXAMPLES

I. Synthesis of Pentaarylcyclopentadiene

(6) The synthesis of pentaarylcyclopentadiene can be effected substantially by two different synthesis routes according to the following reaction schemes:

(7) ##STR00003##

(8) The first reaction pathway I is effected via tetraarylcyclopentadienone as starting substance, whereas the second reaction pathway II is effected via 2,3,4,5-tetraarylcyclopenten-2-one as starting substance.

(9) I. Synthesis route proceeding from tetraarylcyclopentadienone The synthesis of pentaarylcyclopentadiene proceeding from tetraarylcyclopentadienone is based on the studies by Ziegler and Schnell (Ziegler et al., Liebigs Ann. Chem. 445 (1925), 266) and was modified in substantial processing.

Ia) 1,2,3,4,5-Pentaphenylcyclopenta-1,3-dien-5-ol

(10) In a Grignard reaction, proceeding from tetraarylcyclopenta-dienone and an excess of arylmagnesium bromide, 1,2,3,4,5-pentaarylcyclopenta-1,3-dien-5-ol is obtained. In further processing, 1,2,3,4,5-pentaarylcyclopenta-1,3-dien-5-ol is obtained not as described in Ziegler by introducing a hydrogen bromide stream into a solution of the alcohol in glacial acetic acid, but by the reaction of the alcohol with acetyl bromide in toluene. This reaction proceeds particularly well with tertiary alcohols, for example triphenylmethanol.

(11) 46.2 g (0.12 mol) of tetraphenylcyclopentadienone are reacted with 0.61 mol of phenylmagnesium bromide in 400 ml of ether to give 1,2,3,4,5-pentaphenylcyclopenta-1,3-dienol (yield 50.8 g (87%); m.p.: 177-179? C., lit.: 175-176? C., elemental analysis for C35H26O. found: C, 90.98%; H, 5.59%; calc.: C, 90.88%; H, 5.66%.)

Ib) 5-Bromo-1,2,3,4,5-pentaphenylcyclopenta-1,3-diene

(12) The pentaarylcyclopenta-1,3-dien-5-ol reacts with elimination of hydrogen bromide to give 1,2,3,4,5-pentaarylcyclopenta-1,3-diene 1-acetate. This ester is unstable in the presence of hydrogen bromide. With elimination of acetic acid, this gives a 1,2,3,4,5-pentaarylcyclopentadienyl cation, which is stabilized by accepting a bromide ion. With a reaction regime using an excess of acetyl bromide, the reaction proceeds quantitatively.

(13) 50.8 g (0.11 mol) of 1,2,3,4,5-pentaphenylcyclopenta-1,3-dien-5-ol are suspended in 200 ml of toluene. Within 20 minutes, 74 g (0.6 mol) of acetyl bromide are added dropwise at room temperature and then the reaction mixture is boiled under reflux for 2 hours. Towards the end of the reaction, another 2 ml of methanol are added dropwise. Excess acetyl bromide and toluene are distilled off under reduced pressure. The remaining oil crystallized after addition of 100 ml of petroleum ether. The orange precipitate is filtered off with suction, washed with petroleum ether and dried (m.p.: 183-185? C.). Analytically pure orange products are obtained by recrystallization from toluene. (Yield: 52.7 g (91%); m.p.: 189-190? C., lit.: 188-189? C.; elemental analysis for C35H25Br. found: C, 80.2%; H, 4.8%; calc.: C, 80.00%; H, 4.8%).

Ic) 1,2,3,4,5-Pentaphenylcyclopenta-1,3-diene

(14) Subsequently, the 5-bromo-1,2,3,4,5-pentaarylcyclopenta-1,3-diene is reduced in ether with lithium aluminum hydride to give the pentaarylcyclopentadiene hydrocarbon (according to Houben-Weyl 4/1d Reduktion II, Methoden der organischen Chemie (1981) page 397).

(15) Added in portions to a suspension of 11.5 g (0.3 mol) of Li in 150 ml of ether while stirring is a suspension of 52.6 g (0.1 mol) of 5-bromo-1,2,3,4,5-pentaphenylcyclopenta-1,3-diene in 300 ml of ether. The resultant pale yellow-gray suspension is boiled under reflux for another 2 hours to complete the reduction. After cooling to room temperature, excess Li is hydrolyzed first with ice-water and then with dilute hydrochloric acid. The rotary evaporator is then used to distill all volatile organic constituents out of the reaction mixture. The pale yellow crude product is filtered off with suction and washed repeatedly with water. For further purification, it is dried azeotropically with toluene, filtered and then recrystallized (yield 37.3 g (84%); m.p.: 253-256? C. (according to the batch), lit.: 244-246; elemental analysis for C35H26. found: C, 94.8%; H, 5.8%; calc.: C, 94.13%; H, 5.87%; .sup.1H NMR (200 MHz, CDCl3, TMS): ? 7.25-6.92 (multiplet, 25 aromatic H), 5.07 (1 acid H); .sup.13C NMR (broadband-decoupled, 50 MHz, CDCl.sub.3, TMS): 146.5, 144.0, 136.2, 135.8, 130.1, 129.0, 128.5, 128.4, 127.8, 127.6, 126.7, 126.5, 126.3, 62.7 (s, sp3-C); MS-EI spectrum corresponds to literature spectrum RMSD 5094-9).

II. Synthesis route proceeding from 2,3,4,5-tetraarylcyclo-penten-2-one

(16) According to Dielthey et al. (Dielthey, W., Quint, F., J. Prakt. Chem. 2 (1930), 139), proceeding from benzoin and 1,3-diphenylacetone (dibenzyl ketone), 2,3,4,5-tetraarylcyclo-penten-2-one is obtained as the condensation product. 2,3,4,5-Tetraarylcyclopenten-2-one reacts with an excess of aryllithium to give 1,2,3,4,5-pentaarylcyclopenta-2,4-dien-1-ol, which is subsequently converted according to Rio et al. (Rio, G. Sanz, Bull. Soc. Chim. France 12 (1966) 3375) with elimination of water to give very pure pentaarylcyclopentadiene.

IIa. 1,2,3,4,5-Pentaphenylcyclopenta-1,3-diene

(17) 2,3,4,5-Tetraphenylcyclopenten-2-one reacts with an excess of phenyllithium to give 1,2,3,4,5-pentaphenylcyclopenta-2,4-dien-1-ol. 1,2,3,4,5-Pentaphenylcyclopenta-1,3-diene then forms through elimination of water. This method likewise gives very pure products.

(18) 1,2,3,4,5-Pentaphenylcyclopenta-1,3-diene is prepared from 37.8 g (0.098 mol) of 2,3,4,5-tetraphenylcyclopenten-2-one and 0.5 mol of phenyllithium (formed from 7 g (1 mol) of Li and 78.5 g (0.5 mol) of bromobenzene) in 300 ml of ether by a literature method of Rio and Sanz, and purified analogously to method I. The conversion of the 1,2,3,4,5-pentaphenylcyclo-penta-2,4-dien-1-ol to 1,2,3,4,5-pentaphenylcyclopenta-1,3-diene proceeds automatically within the conversion. This gives a yield of 34.9 g (80%), and the product is identical to the C.sub.5HPh.sub.5 prepared by method I.

III. Preparation of the Salts of the Cyclopentadiene Compounds Using the Example of the Cesium Salts

(19) About 100 mg of elemental cesium (Fluka) are washed repeatedly with hexane in order to remove any adhering oils. 1 mmol of the cyclopentadiene compounds is dried under reduced pressure and dissolved in about 20-40 ml of THF. This solution was added to the purified cesium. There is evolution of hydrogen. The suspension is stirred (about 2-4 h) until coloring occurs or no further evolution of hydrogen is observed. The solution is filtered to remove excess cesium. By drawing off the solvent and subsequent sharp drying, the anhydrous cesium salts of the cyclopentadiene compound are obtained.

IV. Production of the Layers

IV.1) Production of the Comparative Material

(20) Deposited on an ITO (indium tin oxide=indium-doped tin oxide) electrode by thermal evaporation is a 200 nm-thick layer of the electron conductor BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline). The counterelectrode used is a 150 nm-thick aluminum layer.

IV.2) Production of Organic Electrically Conductive Layers with Cesium Pentaphenylcyclopentadienide as Dopant

(21) In three further experiments, a cesium pentaphenylcyclopenta-dienide is incorporated into the electrically conductive layer by doping in concentrations of 2%, 5% and 10% relative to the evaporation rate of the BCP.

(22) In the course of a physical characterization, it is found for the current-voltage characteristics of the doped organic components that the current density of the doped layers is well above that of the comparative substrate at the same voltage. When the level of doping is sufficiently small, this effect is nearly proportional to the doping intensity. Increasing current density therefore leads to the conclusion of an increase in the charge carrier density and/or mobility.

IV.3 Production of Organic Electrically Conductive Layers with Rubidium Penta(p-Tolyl)Cyclopentadienide as Dopant

(23) In three further experiments, a rubidium penta(p-tolyl)cyclo-pentadienide is incorporated by doping in concentrations of 2%, 5% and 10% relative to the evaporation rate of BCP.

(24) In the course of a physical characterization, it is found for the current-voltage characteristics of the doped organic components that the current density of the doped layers is well above that of the comparative substrate at the same voltage. When the level of doping is sufficiently small, this effect is nearly proportional to the doping intensity. Increasing current density therefore leads to the conclusion of an increase in the charge carrier density and/or mobility.

(25) The invention has been described in detail with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention covered by the claims which may include the phrase at least one of A, B and C as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in Superguide v. DIRECTV, 69 USPQ2d 1865 (Fed. Cir. 2004).