Method for manufacturing organic electronic devices

Abstract

The present invention relates to a method for manufacturing organic electronic devices including a dipyrannylidene film as an anodic interface layer, the method being carried out in a vacuum and without any exposure to air. The invention also relates to organic devices resulting from the method, more specifically to organic solar cells (OSC).

Claims

1. A process for the manufacture of an organic electronic device, comprising at least the following stages: (i) the deposition by vacuum evaporation, on a substrate, of a film comprising at least one compound of following formula (I): ##STR00003## in which: Xa and Xb, which are identical or different, are chosen from N, P, O, S, Se or Te atoms, R.sub.1, R.sub.2, R.sub.3 and R.sub.4, which are identical or different, represent a group chosen from aryl or heteroaryl rings having from 4 to 10 carbon atoms, said aryl or heteroaryl rings being optionally substituted by one or more halogen atoms or —OH, —CN, —NO.sub.2 groups, alkyl having from 1 to 30 carbon atoms, alkoxy —OC.sub.nH.sub.2n+1 or ester —C(O)OC.sub.nH.sub.2n+1 groups, in which 0≦n≦16, (ii) the deposition under an inert atmosphere of a photosensitive active layer, (iii) optionally, the annealing under an inert atmosphere of the photosensitive active layer deposited during stage (ii), (iv) the deposition under an inert atmosphere of an active layer for the dissociation of the excitons, (v) the deposition under an inert atmosphere of a layer acting as cathode electrode, said process being carried out with the exclusion of air, and wherein the organic electronic device has a power conversion efficiency greater than or equal to 3%.

2. The process as claimed in claim 1, in which the Xa and Xb atoms of the compound of formula (I) are identical and are chosen from O, S or Se atoms.

3. The process as claimed in claim 1, in which the aryl or heteroaryl rings R.sub.1, R.sub.2, R.sub.3 and R.sub.4 of the compound of formula (I) are chosen from phenyl, naphthyl, anthracyl, benzoxazolyl, thiophenyl or alkoxythiophenyl, furyl, pyrrolyl, pyridyl, pyrazyl, pyrazolyl, pyridazyl, pyrimidyl, triazyl, imidazolyl, oxazolyl, indyl, indazolyl, quinolyl and quinoxalyl rings.

4. The process as claimed in claim 1, in which the deposition by vacuum evaporation of stage (i) is carried out in an ultrahigh vacuum chamber.

5. The process as claimed in claim 1, in which the deposition by vacuum evaporation of stage (i) is carried out at a rate of evaporation of less than 1 Å/s.

6. The process as claimed in claim 1, in which the film comprising at least one compound of formula (I) has a thickness of less than 45 nm.

7. The process as claimed in claim 1, in which the substrate is chosen from insulating substrates or conducting substrates.

8. The process as claimed in claim 1, in which the distance between the source of the compound of formula (I) and the substrate is between 10 and 40 cm, during stage (i).

9. The process as claimed in claim 1, in which a stage of deposition of a conducting intermediate layer, is carried out between stages (i) and (ii).

10. The process as claimed in claim 1, in which the deposition of stage (ii) is carried out in a glove box placed under an inert atmosphere of nitrogen or argon.

11. The process as claimed in claim 1, in which the deposition of stage (ii) is carried out by spin coating.

12. The process as claimed in claim 1, in which the annealing of stage (iii) is carried out in a tubular oven, at a temperature of between 30 and 150° C., for a period of time of between 1 minute and 24 hours.

13. The process as claimed in claim 1, in which the deposition of stage (iv) is carried out by the dry route, at a rate of evaporation of less than 1 Å/s.

14. The process as claimed in claim 13, in which the deposition by the dry route is carried out at an annealing temperature of between 80 and 120° C. and under a pressure of between 10.sup.−4 and 10.sup.−8 mbar, for a period of time of between 2 and 4 hours.

15. The process as claimed in claim 1, in which the deposition of stage (v) is carried out in an ultrahigh vacuum chamber.

16. The process as claimed in claim 1, in which the deposition of stage (v) is carried out by the dry route at a rate of evaporation of less than or equal to 3 Å/s.

17. The process as claimed in claim 1, in which the layer acting as cathode electrode deposited during stage (v) is based on aluminum, gold, calcium, copper, samarium, platinum, palladium, chromium, cobalt or iridium.

18. The process as claimed in claim 1, in which the substrate is made of glass or plastic or is based on tin-doped indium oxide (ITO), and the photosensitive active layer is P3HT:PCBM.

19. The process as claimed in claim 1, wherein said active layer for the dissociation of the excitons is based on lithium fluoride (LiF).

20. The process as claimed in claim 1, wherein the organic electronic device has a power conversion efficiency from 3 to 6%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In addition to the preceding provisions, the invention also comprises other provisions which will emerge from the description which will follow, which refers to examples of the implementation of the process of the invention and to the evaluation of OSC devices manufactured according to this process, and also to the appended drawings, in which:

(2) FIG. 1 represents the current/voltage curves of an OSC device according to the invention (light curve: in darkness; dark curve: under AM1.5G illumination (75 mW.Math.cm.sup.−2)),

(3) FIG. 2 represents the EQE spectrum of the device of the invention (curve exhibiting a maximum at 80% for a wavelength of approximately 530 nm) and the absorption spectrum of the ITO/DIPO-Φ.sub.4/PEDOT:PSS/P3HT:PCBM device, and

(4) FIG. 3 shows AFM (2D and 3D) microscopy images of the anode layer of an OSC device according to the invention.

DETAILED DESCRIPTION

EXPERIMENTAL PART

(5) A substrate coated with a film comprising 4,4′-bis(2,6-diphenylpyranylidene) (DIPO-Φ.sub.4) as compound of formula (I) was prepared according to the procedure described below.

(6) The formula of DIPO-Φ.sub.4 is as follows:

(7) ##STR00002##

(8) A—Synthesis of DIPO-Φ.sub.4

(9) Stage 1: Synthesis of 1,5-diphenyl-1,5-pentadione

(10) A solution of glutaryl chloride (10 mmol, 1.3 ml) dissolved in anhydrous dichloromethane (20 ml) is introduced under an inert atmosphere into a 100 ml two-necked round-bottomed flask. Aluminum chloride (30 mmol, 4.00 g) is added to the mixture, which immediately turns orange-yellow in color. A solution of benzene (20 mmol, 1.8 ml) dissolved in anhydrous dichloromethane (10 ml) is added dropwise at ambient temperature. The solution becomes intense red. The mixture is subsequently brought to reflux for 24 hours and turns brown-black in color. The mixture is subsequently brought back to ambient temperature and then run, with stirring, into a crystallizing dish containing 20 ml of water acidified to 10%. A black solid is formed and is then filtered off on a Buchner funnel. The organic phase, which is yellow in color, is subsequently extracted with ethyl acetate, dried over MgSO.sub.4, filtered, concentrated on a rotary evaporator and recrystallized from 20 ml of methanol. The product obtained is a white solid having a weight of 680 mg. The reaction yield is 27%.

(11) TLC (eluent: petroleum ether/ethyl acetate 1:1): 0.75

(12) .sup.1H NMR (CDCl.sub.3, 400 MHz): δ=7.98 (d, 4H, .sup.3J=7.1 Hz), 7.57 (t, 2H, .sup.3J=7.3 Hz), 7.47 (t, 4H, .sup.3J=7.3 Hz), 3.13 (t, 4H, .sup.3J=6.9 Hz), 2.21 (quint., 2H, .sup.3J=6.9 Hz)

(13) Stage 2: Synthesis of 2,6-diphenylpyrylium perchlorate

(14) The 1,5-diphenyl-1,5-pentadione prepared during stage 1 (10 mmol, 2.52 g) is mixed, in a 100 ml two-necked round-bottomed flask, with phosphorus pentasulfide (15 mmol, 3.34 g), acetic acid (60 ml) and FeCl.sub.3 (60 mmol, 6.40 g) and then brought to reflux for 3 hours. The solution then becomes orange and a white precipitate is formed. The precipitate is removed by filtration through a sintered glass funnel and then washed with hot acetic acid. The solution is concentrated on a rotary evaporator and recrystallized by addition of ether (500 ml). The precipitate obtained is filtered off on a sintered glass funnel and then dried in a rotary evaporator. The product obtained is a red solid having a weight of 850 mg. The reaction yield is 24%.

(15) .sup.1H NMR (CD.sub.3CN, 400 MHz): δ=8.90 (t, 1H), 8.52 (d, 2H), 8.18 (d, 4H), 7.60 (t, 4H), 7.50 (t, 2H).

(16) Stage 3: Synthesis of 4,4′-bis(2,6-diphenylpyranylidene) (DIPO-Φ.sub.4)

(17) The solution of 2,6-diphenylpyrylium perchlorate (10 mmol, 3.50 g) is dissolved in 200 ml of distilled acetonitrile in a 250 ml two-necked round-bottomed flask and then the mixture is brought to reflux under an inert atmosphere for 2 hours. Zinc powder (30 mmol, 1.96 g) is added in small fractions and the mixture is brought to reflux for 24 hours. The solution is filtered, rinsed with toluene and evaporated on a rotary evaporator. A black oil is obtained which is recrystallized from a hexane/ethanol 1:1 mixture. After purification by TLC (eluent: petroleum ether/ethyl acetate 8:2), a black solid weighing 650 mg is obtained. The reaction yield is 13%.

(18) IR (cm.sup.−1): 2920, 1650, 1605, 1550, 1488, 1441, 1229, 1071, 750, 685.

(19) B—Manufacture of an Organic Solar Cell (OSC) According to the Process of the Invention

(20) The preparation of the OSC devices of the invention takes place in several: A 1st stage which has the objective of preparing an ITO substrate with a width of 10 mm and a length of 25 mm, to avoid any short-circuit phenomenon. An ITO electrode on a glass support is immersed with an FeCl.sub.3+HCl solution heated at 50° C. for 2 minutes, successively rinsed in different solvent baths: ethyl acetate, Decon (5% aqueous solution), ethanol and acetone, and then stripped in a UV/ozone chamber by forced oxidation. A 2nd stage of deposition of 4,4′-bis(2,6-diphenylpyranylidene) (DIPO-Φ.sub.4) on a glass/ITO substrate by vacuum evaporation (pressure=10.sup.−7 mbar; rate of deposition=0.1 Å/s), to form a layer with a thickness of 10 nm. The distance between the crucible (crucible made of molybdenum covered with alumina) containing DIPO-Φ.sub.4 and the glass/ITO substrate is 35 cm. The crucible is heated by the Joule effect (0.5 V, 50 A , 25 W). The thickness of the layer is monitored using a quartz balance calibrated for aluminum tris(8-hydroxyquinolinate) (Alq3) (vibrational frequency=6.01 MHz, ±1%). The Alq3 molecule is used as reference standard for the deposition of all the organic molecules. The frequency of the quartz crystal of 6.01 MHz is the nominal working frequency. A 3rd stage during which the glass/ITO/DIPO-Φ.sub.4 substrate is brought back to atmospheric pressure under an inert nitrogen atmosphere and then transferred into a glove box via an airlock. A conducting intermediate layer of PEDOT:PSS (concentrated suspension at a level of 0.29% by weight in aqueous phase, Sigma-Aldrich) is deposited by spin coating at a rate of 2000 revolutions/min for 50 seconds. A 4th stage during which the glass/ITO/DIPO-Φ.sub.4/PEDOT:PSS substrate is covered with a deposit of a photosensitive active layer of P3HT:PCBM at the following concentrations: 15 mg P3HT and 12 mg PCBM (in 1 ml of chlorobenzene), at 1000 revolutions/min for 20 seconds, 1200 revolutions/min for 20 seconds and finally 2000 revolutions/min for 10 seconds. The thicknesses obtained by this method are of the order of 120±10 nm. A 5th stage during which the glass/ITO/DIPO-Φ.sub.4/PEDOT:PSS/P3HT:PCBM device is subsequently transferred into a UHV (Ultra High Vacuum) chamber where deposition of lithium fluoride LiF (Sigma-Aldrich) by thermal evaporation under stable evaporation conditions of 0.01 Å/s, until a layer having a thickness of 0.5 nm is obtained, and then deposition of aluminum by thermal evaporation under stable evaporation conditions of 0.4 Å/s and under a pressure of 10.sup.−7 mbar, until an aluminum layer with a thickness of 80 nm is obtained, are successively carried out. A 6th stage during which the glass/ITO/DIPO-Φ.sub.4/PEDOT:PSS/P3HT:PCBM/LiF/Al device is subsequently transferred into a glove box placed at atmospheric pressure and under an inert nitrogen atmosphere via an airlock.

(21) Finally, deposition of silver lacquer (area ˜1×1 mm.sup.2) is carried out using a fine object (needle tip) on the aluminum layer in order to make possible good electrical contact of the aluminum electrode. Once deposited, the lacquer is dried at ambient temperature for 45 minutes.

(22) C—Characterization of the OSC Device of the Invention

(23) The current/voltage characteristic of the devices in darkness and under illumination are measured under an inert nitrogen atmosphere using a device for the physical measurement of currents (Keithley 2406) and a microtip station.

(24) The characteristics in darkness are determined by placing a black veil over the devices in order to prevent diffused light from having influence.

(25) The current/voltage characteristics of the devices under illumination are measured on an optical bench equipped:

(26) 1) with a xenon lamp (Oriel, 150 W) which simulates the spectrum of the sun and delivers a power of 75 or 100 mW.Math.cm.sup.−2 at the OSC devices,

(27) 2) with a monochromator (Cornerstone CS120),

(28) 3) with an IR filter placed between the lamp and the OSC devices in order to prevent the latter from overheating,

(29) 4) with synchronous detection (of HDTS brand), and

(30) 5) with an optical chopper (of Lot Oriel brand).

(31) The solar simulator is calibrated so as to release the solar nominal power such as has been set by international conventions for this type of device (75 or 100 mW/cm.sup.2). The measurements can be carried out under white light or under monochromatic light. Under white light, the component is contacted using the microtip station and is exposed to light using the solar simulator. The electrical measurement device (Keithley 2406) records under zero or variable field the current extracted from the OSC device of the invention. This measurement makes it possible to determine the external conversion efficiency PCE (Power Conversion Efficiency) of the device.

(32) The current/voltage characteristics in darkness and under illumination by white light make it possible to evaluate the performance and the behavior of the OSC devices of the invention. The following parameters can thus be defined: the short-circuit current Isc obtained for a zero voltage, this current being proportional to the incident illumination (Jsc=Isc/S, where S is the area of the device), the open-circuit voltage Voc measured for a zero current, Imax and Vmax are the IN coordinates (Pmax=Imax×Vmax), the Form Factor (FF), equal to: FF=(Vmax×Imax)/(Voc×Isc)

(33) The current/voltage curves obtained for the OSC device of the invention are represented in FIG. 1 and the corresponding main photovoltaic characteristics are collated in the following Table I:

(34) TABLE-US-00001 TABLE I Vmax Imax Isc Voc Photogenerated current Jsc FF PCE (mV) (μA) (μA) (mV) (mA .Math. cm.sup.−2) (%) (%) 366 0.516 0.766 550 17.1 45 6.0

(35) It is found that the OSC device of the invention exhibits a better performance than those obtained with the devices described in the application WO 2011/045478 and in particular: the open-circuit voltages Voc are superior, the short-circuit currents Isc and the photocurrent densities Jsc are superior.

(36) Consequently, the external conversion efficiency (PCE=6.0% instead of 1.5%) is much greater than that of the devices described in application WO 2011/045478.

(37) Under monochromatic illumination, the light of the lamp passes through a monochromator (Cornerstone CS120) and a pulse chopper to release a pulsed monochromatic light. The electrical measurement is then carried out using synchronous detection. This type of measurement makes it possible to characterize the action spectrum and the external quantum efficiency (EQE) of the photovoltaic device. FIG. 2 presents the EQE characteristics of the OSC device of the invention. It is found that the EQE spectrum follows the absorption spectrum of the P3HT:PCBM active material with a very high maximum at 80% for a wavelength of approximately 530 nm.

(38) Finally, FIG. 3 shows AFM (2D and 3D) microscopy images which reveal a needle-shaped nanostructuring of the anode layer of the OSC device of the invention.