Hole transport material

Abstract

The invention relates to 2,2,7,7-tetrakis-(N,N-di-4-methoxy-3-methylphenylamine)-9,9-spirofluorene, to a process for its preparation, and to its use as hole transport material for electronic or optoelectronic devices, especially for solid-state dye-sensitized solar cells.

Claims

1. A compound of formula (I) ##STR00009##

2. A process for the preparation of the compound according to claim 1 comprising reacting 2,2,7,7-tetrabromo-9,9-spirobifluorene in a Buchwald-Hartwig amination with bis(4-methoxy-3-methylphenylamine).

3. A process according to claim 2 in which the reaction is carried out at temperatures between 100 C. and 140 C.

4. Composition comprising the compound of formula (I) according to claim 1 and at least one solvent.

5. Electronic or optoelectronic device comprising the compound of formula (I) according to claim 1.

6. Device according to claim 5 which is an organic electroluminescent device, an organically integrated circuit, an organic field-effect transistor, an organic thin-film transistor, an organic light-emitting transistor, a solar cell, an organic optical detector, an organic photoreceptor, an organic field-quench device, a light-emitting electrochemical cell or an organic laser diode, an organic plasmon emitting device, an electrophotography device or a wave converter.

7. Device according to claim 5 which is a solid-state dye-sensitized solar cell or a perovskite containing solar cell.

8. Device according to claim 5, characterized in that the compound of formula (I) is employed as hole transport material.

9. Charge transport layer comprising a compound of formula (I) according to claim 1.

10. A layer according to claim 9 which is a photosensitized nanoparticle layer comprising a sensitizing dye or perovskite and the compound of formula (I).

11. A layer according to claim 9 further comprising an insulator.

12. A layer according to claim 9 comprising semiconductor oxide nanoparticles.

13. Device according to claim 7 comprising a charge transport layer comprising a compound of formula I.

14. A module comprising a device according to claim 5.

15. The compound bis(4-methoxy-3-methylphenylamine).

16. A process for the preparation of bis(4-methoxy-3-methylphenylamine) comprising reacting 4-Bromo-1-methoxy-2-methylbenzene in a Buchwald-Hartwig amination with 4-methoxy-3-methylphenylaniline.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 represents hole mobility of the invention and reference materials.

(2) The present invention will now be illustrated, without limiting its scope, by way of the following examples. Even without further comments, it is assumed that a person skilled in the art will be able to utilize the above description in the broadest scope. The preferred embodiments and examples should therefore merely be regarded as descriptive disclosure which is absolutely not limiting in any way.

EXAMPLES

Example 1

Synthesis of 2,2,7,7-tetrakis-(N,N-di-4-methoxy-3-methylphenylamine)-9,9-spirobifluorene

Step 1: Synthesis of bis(4-methoxy-3-methylphenylamine)

(3) ##STR00004##

(4) 4-Bromo-1-methoxy-2-methylbenzene (3.134 mg, 15.6 mmol), sodium tert-butoxide (3.053 g, 32 mmol), Palladium(II) acetate (69 mg, 0.3 mmol), 1,1-bis(diphenylphosphino)ferrocene (DPPF) (169 mg, 0.3 mmol) are dissolved in toluene (10 ml) in a 4-neck flask with condenser. The reaction mixture is stirred under N.sub.2 flow for 5 minutes, then 4-methoxy-3-methylphenylaniline (2.064 g, 15.0 mmol) and 40 mL of toluene are added. The mixture is heated to 120 C. for 21 h. After the reaction, the reaction mixture is filtered. After concentration by rotary evaporator and purification by flash column chromatography over silica gel (hexane/EtOAc 2%->20%) the product is obtained as an orange viscous oil. This oil is recrystallized by hexane thermally, to obtain bis(4-methoxy-3-methylphenyl)amine as white solid [2.725 g, 10.6 mmol, yield 70.4%)].

(5) C.sub.16H.sub.19NO.sub.2, MW 257.33, Exact MS 257, GC-MS 257[M]+).

Step 2: Synthesis of 2,2,7,7-tetrakis-(N,N-di-4-methoxy-3-methylphenylamine)-9,9-spirobifluorene

(6) ##STR00005##

(7) 2,2,7,7-tetrabromo-9,9-spirobifluorene (639 mg, 1.01 mmol), sodium tert-butoxide (608 g, 6.33 mmol), Palladium(II) acetate (29 mg, 0.13 mmol), 2-Dicyclohexylphosphino-2,6-dimethoxybiphenyl (SPhos) (41 mg, 0.10 mmol) are dissolved in toluene (10 mL) in a 4-neck flask with condenser. The reaction mixture is stirred under N.sub.2 flow for 5 minutes, then bis(4-methoxy-3-methylphenylamine) prepared according to step 1 (1.253 g, 4.87 mmol) and toluene (20 mL) are added. The mixture is heated to 120 C. for 16 h. After the reaction, the reaction mixture is filtered. After concentration by rotary evaporator and purification by flash column chromatography over silica gel (hexane/EtOAc 5%->40%) the product is obtained as a beige amorphous solid [1.082 g, 0.81 mmol, yield 80.0%].

(8) C.sub.89H.sub.84N.sub.4O.sub.8, MW 1337.64, Exact MS 1336, LC-ESI-MS 1337.7 [M+H]+).

Example 2

Synthesis of the reference material spiro-OMeTAD

(9) ##STR00006##

(10) 2,2,7,7-tetrabromo-9,9-spirobifluorene (1.896 mg, 3.0 mmol), sodium tert-butoxide (1.822 g, 19 mmol), Palladium(II) acetate (1.6 mg, 0.01 mmol), 2-Dicyclohexylphosphino-2,6-dimethoxybiphenyl (SPhos) (6.8 mg, 0.02 mmol) are dissolved in toluene (10 mL) in a 4-neck flask with condenser. The reaction mixture is stirred under N.sub.2 flow for 5 minutes, then bis(4-methoxyphenylamine) (3.620 g, 15.7 mmol) and toluene (25 mL) are added. The mixture is heated to 120 C. for 70 h. After the reaction, the reaction mixture is filtered and concentrated. The product is recrystallized from dichloromethane and methanol.

Example 3

Synthesis of the reference material 2,2,7,7-tetrakis-(N,N-di-4-methoxy-3,6-dimethylphenylamine)-9,9-spirobifluorene

Step 1: Synthesis of bis(4-methoxy-3,6-dimethylphenylamine)

(11) ##STR00007##

(12) 5-Bromo-2-methoxy-1,3-dimethylbenzene (4.179 mg, 21.9 mmol), sodium tert-butoxide (4.468 g, 46.5 mmol), Palladium(II) acetate (93 mg, 0.4 mmol), 1,1-bis(diphenylphosphino)ferrocene (DPPF) (220 mg, 0.4 mmol) are dissolved in toluene (20 ml) in a 4-neck flask with condenser. The reaction mixture is stirred under N.sub.2 flow for 5 minutes, then 4-methoxy-3,5-dimethylphenylaniline (3.032 g, 20.0 mmol) and 60 mL of toluene are added. The mixture is heated to 120 C. for 20 h. After the reaction, the reaction mixture is filtered. After concentration by rotary evaporator and purification by flash column chromatography over silica gel (hexane/EtOAc 2%->20%) the product is obtained as an orange viscous oil. This oil is thermally recrystallized by hexane to obtain bis(4-methoxy-3,5-methylphenyl)amine as white solid [2.961 g, 10.37 mmol, yield 51.7%)].

(13) C.sub.18H.sub.23NO.sub.2, MW 285.38, Exact MS 285, GC-MS 285.1 [M].sup.+ UV max 288 nm.

Step 2: Synthesis of 2,2,7,7-tetrakis-(N,N-di-4-methoxy-3,6-dimethylphenylamine)-9,9-spirobifluorene

(14) ##STR00008##

(15) 2,2,7,7-tetrabromo-9,9-spirobifluorene (316 mg, 0.5 mmol), sodium tert-butoxide (629 g, 6.55 mmol), Palladium(II) acetate (12 mg, 0.05 mmol), 2-Dicyclohexylphosphino-2,6-dimethoxybiphenyl (SPhos) (22 mg, 0.05 mmol) are dissolved in toluene (5 mL) in a 4-neck flask with condenser. The reaction mixture is stirred under N.sub.2 flow for 5 minutes, then bis(4-methoxy-3,5-dimethylphenylamine) (C-1) (316 g, 1.11 mmol) and toluene (25 mL) are added. The mixture is heated to 120 C. for 50 min. After the reaction, the reaction mixture is filtered. After concentration by rotary evaporator and purification by flash column chromatography over silica gel (hexane/EtOAc 5%->80%) the product is obtained as a beige amorphos solid [190 mg, 0.13 mmol, yield 26.6%].

(16) C.sub.97H.sub.100N.sub.4O.sub.8, MW 1449.85, Exact MS 1448, LC-ESI-MS 1449.1 [M+H].sup.+).

Example A

Solubility of the compounds of Examples 1, 2 and 3

(17) General Description:

(18) A solution for a spin-coat is prepared in a N.sub.2 glove box as follows: at first, 20 mg of a hole transport material is dissolved in 95 L of chlorobenzene. The hole transport material needs to be dissolved completely. A mother solution of lithium bis(trifluorosulfonyl)imide (LiTFSI) and tert-butylpyridine (TBP) is prepared separately at room temperature and is added to the hole transporter solution to set the molar ratio to [hole transporter]:[LiTFSI]:[TBP]=10:1:10 at room temperature. Thus the final volume of the solution is 100 L.

(19) The solubility of the HTMs according to examples 1, 2 and 3 are evaluated qualitatively:

(20) 1 means: 20 mg of HTM is completely dissolved without heating

(21) 2 means: HTM is dissolved after heating to 80 C.

(22) 3 means: HTM is dissolved after adding salt and base solution and heating to 80 C.

(23) 4 means: HTM is dissolved after adding another 50 L of chlorobenzene and heat to 80 C. (final folume 150 l).

(24) The result is shown in Table 1:

(25) TABLE-US-00001 1 2 3 4 Example 2 (ref) Example 3 (ref.) Example 1

(26) The hole transport material according to the invention has better solubility than the reference materials.

Example B

(27) Using the solution as described in Example A, a solid state dye-sensitized solar cell is fabricated according to Lukas Schmid-Mende and Michael Grtzel, Thin Solid Films, 500, 2006, 296-301.

(28) After cleaning the patterned ITO/ATO substrates (2020 mm) with Helmanex and water, the TiO.sub.2 compact layer is prepared by a sol-gel method using 60 mM TiCl.sub.4 aqueous solution at 75 C. for 30 min for three times. A nanocrystalline TiO.sub.2 layer is fabricated through screen printing of a TiO.sub.2 paste containing 30 nm-sized anatase particles (JGC C&C PST-30NRD) followed by sintering at 500 C. for 30 min. A top TiO.sub.2 coat is deposited by sol-gel method using 60 mM TiCl.sub.4 aqueous solution at 75 C. for 30 min once and sintered at 500 C. for 30 min. Obtained TiO.sub.2 substrates are sensitized by dipping in a 0.3 mM solution of amphiphilic polypyridyl ruthenium complex, cis-RuLL'(SCN).sub.2 (L=4,4-dicarboxylic acid-2,2-bipyridine, L=4,4-dinonyl-2,2-bipyridine, Z907) with 0.075 mM of bis-(3,3-dimethyl-butyl)-phosphinic acid (DINHOP) in acetonitrile:tert-butanol (1:1 vol %) and placed in a refrigerator overnight. The hole transport materials are independently coated by spin-coater. 40 L of the solution is put onto one substrate with waiting time for 30 sec and spinning condition of 2500 rpm for 30 sec. To finish the device fabrication, a 200 nm of Ag electrode is evaporated on top. This procedure results in two cells on one substrate. The measurements for performance are done without sealing he cells.

(29) Current-Voltage characteristics are measured by a source meter (Keithley 2400) under simulated AM 1.5 G sunlight at 100 mW cm.sup.2 irradiance, generated using a solar simulator (L11 Peccell Technologies) and calibrated using a calibrated silicon reference cell (Bukou Keiki, BS-520). The solar cells are masked with a metal aperture to define the active area which is typically 0.16 cm.sup.2.

(30) The cell structure measured in this experiment and their current-voltage characteristics are summarized in table 2.

(31) TABLE-US-00002 TABLE 2 current-voltage property of each cell: J.sub.sc/mA V.sub.OC/ HTM cm.sup.2 V FF PCE/% Example 2 (ref.) 3.67 0.744 0.532 1.45 Example 3 (ref.) 1.92 0.734 0.493 0.69 Example 1 2.74 0.787 0.669 1.43

(32) The result indicates, that the inventive compound of formula (I) has a comparable conversion efficiency with better solubility than spiro-OMeTAD.

Example C

Hole Mobility

(33) The hole mobility of the inventive compound 2,2,7,7-tetrakis-(N,N-di-4-methoxy-3-methylphenylamine)-9,9-spirobifluorene is measured and the value is compared with those of the reference materials according to example 2 and example 3.

(34) The structure of the measurement cell is ITO(200 nm)/PEDOT-PSS(150 nm)/HTM(400 nm)/Au(60 nm).

(35) PEDOT-PSS means poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate).

(36) The measurement is carried out using four cells for each HTM by means of impedance spectroscopy. (Ref. 1. H. Martens et al., Phys. Rev. B, 60, R8489 (1999), Ref. 2. S. Ishihara, et al., Proc. of IDW'09, p 1085 (2009)). In the impedance measurement, a direct current (dc) voltage is applied to the test cell in order to inject holes from an anode. The hole mobility is determined under the dc field intensity of 10.sup.5V/cm. The measurement result is shown in FIG. 1 and in Table 3.

(37) TABLE-US-00003 TABLE 3 Hole mobility [cm.sup.2/Vs) Example 2 (ref) = A 1.08E04 Example 3 (ref.) = C 9.34E06 Example 1 = B 1.29E04

(38) The hole mobility of the inventive compound 2,2,7,7-tetrakis-(N,N-di-4-methoxy-3-methylphenylamine)-9,9-spirobifluorene is larger than the hole mobility of spiro-OMeTAD and more than one order of magnitude larger than the hole mobility of the reference example 3. The result of FIG. 1 can well interpret the result of Table 2 in terms of the hole mobility of the used hole transport material.