Organic dye with improved efficiency and uses thereof in photovoltaic cells

Abstract

An organic dye corresponding to one of the following structures (I) or (II): eD-pi-conjugated chromophore-L-A (I), or A-L-pi-conjugated chromophore-eD (II), where eD represents an electron donor segment, L represents a covalent bond or a spacer segment and in particular a pi-conjugated spacer segment, A represents an electron acceptor segment capable of forming a covalent bond with a semiconductor, in which the pi-conjugated chromophore comprises at least one unit of formula (III): ##STR00001##
in which the radicals R1 and R2, which are identical or different, represent an optionally substituted aryl group; the radicals R3 to R8, which are identical or different, represent a hydrogen, an optionally substituted alkyl group or an optionally substituted aryl group; and X1 and X2, which are identical or different, are chosen from S, Se and O.

Claims

1. Organic dye corresponding to one of the following structures (I) or (II):
eD-pi-conjugated chromophore-L-A(I)
A-L-pi-conjugated chromophore-eD(II) where: eD represents an electron-donor segment, L represents a covalent bond or a spacer segment and in particular a pi-conjugated spacer segment, A represents an electron-attractor segment capable of forming a covalent bond with a semiconductor, wherein the pi-conjugated chromophore comprises at least one unit of formula ##STR00024## where: the radicals R.sub.1 and R.sub.2, the same or different, are an optionally substituted aryl group; the radicals R.sub.3 to R.sub.8, the same or different, are a hydrogen, an optionally substituted alkyl group or optionally substituted aryl group; and X.sub.1 and X.sub.2, the same or different are selected from among S, Se and O.

2. The organic dye according to claim 1, wherein said pair (X.sub.1,X.sub.2) represents (S,S), (O,O) or (Se,Se) and in particular (S,S).

3. The organic dye according to claim 1, wherein in said unit (III), said radicals R.sub.4 to R.sub.6 are the same and/or the radicals R.sub.7 and R.sub.8 are the same, said radicals R.sub.4 to R.sub.6 preferably all representing a hydrogen and/or the radicals R.sub.7 and R.sub.8 preferably all representing a hydrogen.

4. The organic dye according to claim 1, wherein in said unit (III), said radical R.sub.3 represents a hydrogen.

5. The organic dye according to claim 1, wherein in said unit (III), said radicals R.sub.1 and R.sub.2 are the same and represent an optionally substituted aryl group and in particular an aryl group substituted by an optionally substituted alkyl group.

6. The organic dye according to claim 1, wherein said unit (III) is of formula (IV): ##STR00025## where the radicals R.sub.1 and R.sub.2 are the same and represent C.sub.6H.sub.4C.sub.6H.sub.13.

7. The organic dye according to claim 1, wherein said electron-donor segment (eD) is an amino group of (Z.sub.1)(Z.sub.2)N-type with Z.sub.1 and Z.sub.2, the same or different, representing an optionally substituted alkyl group or optionally substituted aryl group.

8. The organic dye according to claim 1, wherein said electron-acceptor segment (A) is a carboxylic acid group, cyanoacrylic acid group, phosphonic group, dithiocarboic group or a group corresponding to any one of the following formulas: ##STR00026##

9. The organic dye according to claim 1, wherein said spacer L is a pi-conjugated function such as an optionally substituted alkenylene or alkynylene chain and/or an optionally substituted arylene chain.

10. The organic dye according to claim 1, wherein said organic dye is selected from among the following compounds: ##STR00027##

11. Use of an organic dye such as defined in claim 1 as photosensitizer in a photovoltaic device.

12. Photovoltaic device having a nanostructured semiconductor metal oxide layer sensitized by at least one organic dye such as defined in claim 1.

13. The photovoltaic device according to claim 12, wherein said photovoltaic device further comprises two electrodes, designated anode and counter-electrode in the invention, and separated from each other by an electrolyte and optionally polymer separators.

14. The photovoltaic device according to claim 12, wherein the semiconductor metal oxide is a binary, tertiary or quaternary metal oxide.

15. The photovoltaic device according to claim 12, wherein said electrolyte is a liquid, an ionic liquid, a gel or a solid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic illustration of a photovoltaic cell such as described in the article by O'Regan and Grtzel, 1991 [1].

(2) FIG. 2 gives the absorption spectrum of the dyes of the invention (YKP88, YKP89, YKP137 and DJ214) in solution in chloroform, compared with the reference dyes RK1 and RKF, published in the article by Joly et al, 2015 [17].

(3) FIG. 3 illustrates the stability of the dyes of the present invention (YKP88 and YKP89) compared with reference dyes (RK1 et RKF) as a function of irradiation time at 1000 W/m.sup.2 with UV filter at 65 C.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

(4) I. Synthesis of the YKP88 Dye.

I.1. Methyl 5-bromo-2-(thiophen-2-yl)benzoate [YKC4P80]

(5) ##STR00008##

(6) In an argon atmosphere, methyl 5-bromo-2-iodobenzoate (2.50 g, 7.33 mmol) and tetrakis(triphenylphosphine)palladium (423 mg, 5 mol %) were dissolved in 30 mL of tetrahydrofuran (THF). At ambient temperature 2-thienylzinc bromide (1.67 g, 7.33 mmol) was added dropwise, the solution was vigorously stirred and heated to 70 C. overnight. The reaction was stopped with a 2M solution of HCl and the organic phase extracted with diethylether, washed with water and brine, dried over sodium sulfate (Na.sub.2SO.sub.4), filtered and concentrated in vacuo. The crude product was purified by silica gel chromatography eluting with n-hexane/dichloromethane (DCM): 9:1 (v/v) then 7:3 (v/v), whereby a colourless oil was obtained (2.15 g, 7.24 mmol, 98.7%).

(7) .sup.1H NMR (CDCl.sub.3, 200 MHz): =7.86 (dd, 1H, 1=4.8 Hz, 1=0.3 Hz, H.sub.ar), 7.61 (dd, 1H, J=2.1 Hz, 1=8.3 Hz, H.sub.ar), 7.35 (m, 2H, H.sub.ar), 7.04 (m, 2H, H.sub.ar), 3.75 (s, 3H).

(8) .sup.13C NMR (CDCl.sub.3, 50 MHz): =167.3; 141.1; 134.2; 134.1; 133.3; 133.0; 132.5; 127.7; 127.1; 136.6; 121.9; 62.1; 14.3.

I.2. 6-bromo-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophene [YKC4P81]

(9) ##STR00009##

(10) In an argon atmosphere, (4-hexylphenyl)magnesium bromide was previously prepared from 1(4-bromophenyl)hexane (2.0 g, 8.29 mmol) and magnesium (202 mg, 8.29 mmol, 1 eq) in 10 mL of freshly distilled THF. This reaction mixture was placed under reflux for 1 h. In a second flask, methyl 5-bromo-2-(thiophen-2-yl)benzoate [YKC4P80] (1 g, 3.37 mmol) was solubilized in 15 mL of THF. Grignard reagent was added dropwise and the solution heated under reflux for 5 h. After cooling to ambient temperature, the crude mixture was poured into water. The organic phase was extracted twice with ethyl acetate and washed with water and brine, dried over Na.sub.2SO.sub.4, filtered and concentrated in vacuo. The crude product was dissolved in glacial acetic acid (40 mL). After 30 min, 4 mL of concentrated HCl were added dropwise and the mixture brought under reflux to 120 C. for 5 h. After return to ambient temperature, the acetic acid was removed by rotary evaporation and the crude product extracted with pentane. The organic layer was washed several times with water and dried over Na.sub.2SO.sub.4, filtered and concentrated in vacuo. The crude product was purified by silica gel chromatography eluting with n-hexane, whereby a colourless oil was obtained (1.40 g, 2.45 mmol, 72.8%).

(11) .sup.1H NMR (CDCl.sub.3, 400 MHz): =74.7 (d, 1H, J=0.7 Hz), 7.40 (dd, 1H, J=1.8 Hz, J=8.0 Hz, H.sub.ar), 7.31 (d, 1H, J=4.9 Hz, H.sub.ar), 7.30 (d, 1H, 1=8.0 Hz, H.sub.ar), 7.05 (ABq, 8H, ab=13.3 Hz, J=8.38 Hz, H.sub.ar), 6.99 (d, 1H, J=4.9 Hz, H.sub.ar), 2.54 (t, 4H), 1.57 (m, 4H), 1.29 (m, 12H), 0.87 (t, 6H).

(12) .sup.13C NMR (CDCl.sub.3, 100 MHz): =156.17; 155.54; 141.42; 414.00; 139.69; 136.06; 130.54; 129.32; 128.44; 128.16; 127.44; 122.91; 120.25; 118.94; 35.33; 31.50; 31.11; 28.91; 22.38; 13.87.

I.3. 4,4-bis(4-hexylphenyl)-N,N-diphenyl-4H-indeno[1,2-b]thiophen-6-amine [YKC4P84]

(13) ##STR00010##

(14) In an argon atmosphere, tris(dibenzylideneacetone) dipalladium (Pd.sub.2dba.sub.3) (4 mg, 4.37 mol) and tri-tert-butylphosphine tetrafluoroborate (2.54 mg, 8.75 mol) were dissolved in anhydrous toluene (5 mL). After agitation for 15 min, a solution of 6-bromo-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophene [YKC4P81] (250 mg, 437.3 mol) and diphenylamine (81.4 mg, 481.0 mol) in anhydrous toluene (10 mL) was added. Potassium tert-butoxide (161.94 mg, 1.44 mmol, 3.3 eq) was added and the resulting mixture agitated for 30 min at ambient temperature, before being placed under reflux for 48 h. The mixture was then filtered through Celite and poured into HCl (2 M). The organic phase was extracted with DCM, dried over Na.sub.2SO.sub.4 and concentrated. The crude oil was purified by silica gel chromatography eluting with n-hexane/DCM: 9:1 (v/v) whereby a pale yellow oil was obtained (266 mg, 403 mol, 92.2%).

(15) .sup.1H NMR (CDCl.sub.3, 400 MHz): =7.28 (d, 1H, J=8.2 Hz, H.sub.ar), 7.22 (d, 1H, J=8.2 Hz, H.sub.ar), 7.22 (S, 1H, H.sub.ar), 7.18 (m, 4H, H.sub.ar), 7.04 (m, 7H, H.sub.ar), 6.98 (m, 7H, H.sub.ar), 6.95 (m, 1H, H.sub.ar), 6.93 (d, 1H, J=2.1 Hz, H.sub.ar), 2.53 (t, 4H, CH.sub.2), 1.55 (m, 4H, CH.sub.2), 1.28 (m, 12H, CH.sub.2), 0.87 (t, 6H, CH.sub.3).

(16) .sup.13C NMR (CDCl.sub.3, 100 MHz): =154.99; 147.50; 145.37; 141.69; 140.98; 131.91; 128.87; 127.92; 127.53; 126.74; 123.69; 123.01; 122.95; 122.53; 119.56; 62.6; 35.31; 31.52; 31.16; 29.49; 28.89; 22.39; 13.88.

I.4. 4-(7-(6-(diphenylamino)-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)benzaldehyde [YKC4P87]

(17) ##STR00011##

(18) In an argon atmosphere, 4,4-bis(4-hexylphenyl)-N,N-diphenyl-4H-indeno[1,2-b]thiophen-6-amine (240 mg, 364 mol) was dissolved in distilled THF (15 mL). After bringing the solution to 78 C., n-butyllithium (n-BuLi) (279 L, 418 mol, 1.15 eq) was added. The solution was left under agitation for 1 h at 78 C. before adding a solution of trimethyl tin chloride (Me.sub.3SnCl) (545 L, 545 mol, 1.5 eq) in n-hexane at 78 C. After return to ambient temperature, the solution was left under agitation for 2 h. The reaction was stopped with a saturated ammonium chloride solution. The organic phase was extracted with n-hexane, washed with water and dried over Na.sub.2SO.sub.4, filtered and concentrated in vacuo. The resulting oil was subjected without further purification to Stille coupling with 4-bromo-7-(4-formylbenzyl)-2,1,3-benzothiadiazole (93 mg, 291 mol, 0.8 eq). The stannic product was placed under an argon atmosphere with Pd.sub.2dba.sub.3 (6.66 mg, 7.27 mol, 2 mol %) and Tri(o-tolyl)phosphine (P(o-tolyl).sub.3) (4.41 mg, 14.55 mol, 4 mol %). The products were dissolved in anhydrous toluene (20 mL) and placed under reflux for 24 h. The mixture was then poured into HCl (2 M). The organic phase was extracted with DCM, washed with water, dried over Na.sub.2SO.sub.4 and concentrated. The crude solid was purified by silica gel chromatography eluting with n-hexane/DCM: 6:4 (v/v), whereby a dark red solid of aldehyde type was obtained (195 mg, 217 mol, 74.6%).

(19) .sup.1H NMR (CD.sub.2Cl.sub.2, 400 MHz): =10.09 (s, 1H, CHO), 8.15 (s, 1H, H.sub.ar), 8.10 (ABq, 4H, ab=65.6 Hz, J=8.3 Hz, H.sub.ar), 7.88 (ABq, 2H, ab=60.9 Hz, J=7.6 Hz, H.sub.ar), 7.42 (d, 2H, J=8.2 Hz, H.sub.ar), 7.23 (m, 4H, H.sub.ar), 7.15 (m, 5H, H.sub.ar), 7.08-6.98 (m, 12H, H.sub.ar), 2.56 (t, 4H, J=7.6 Hz, CH.sub.2), 1.57 (m, 4H, CH.sub.2), 1.30 (m, 12H, CH.sub.2), 0.87 (t, 6H, J=6.7 Hz, CH.sub.3).

(20) .sup.13C NMR (CD2Cl2, 100 MHz): =192.00; 156.15; 155.56; 154,05; 152.73; 147.85; 146.87; 143.54; 143.43; 142.03; 141.95; 141.49; 136.09; 131.59; 130.73; 130.00; 129.51; 129.25; 128.62; 128.36; 128.02; 124.60; 124.28; 123.32; 123.05; 122.14; 120.60; 63.59; 35.75; 32.03; 31.79; 29.40; 22.91; 14.16.

I.5. 2-cyano-3-(4-(7-(6-(diphenylamino)-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)phenyl)acrylic Acid [YKP88]

(21) ##STR00012##

(22) In an argon atmosphere, 4-(7-(6-(diphenylamino)-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)benzaldehyde [YKC4P87] (180 mg, 200 mol) and cyanoacetic acid (85 mg, 1 mmol, 5 eq) were dissolved in a mixture of acetonitrile (9 mL) and chloroform (9 mL). A catalytic amount of piperidine was added and the solution placed under reflux for 3 h. The solvent was removed under reduced pressure and the remaining solid was dissolved in chloroform. The organic phase was washed with a 2M solution of HCl, dried over Na.sub.2SO.sub.4 and concentrated. The crude solid was purified by silica gel chromatography eluting first with DCM, then DCM/methanol (MeOH): 95:5 (v/v) and finally DCM/MeOH/Acetic acid: 90:5:5 (v/v), whereby the corresponding dye was obtained in the form of a dark red solid (179.3 mg, 186 mol, 92.7%).

(23) .sup.1H NMR (THF-d.sub.8, 400 MHz): =8.33 (s, 1H, H.sub.ar), 8.25 (ABq, 4H, ab=39.9 Hz, J=8.2 Hz, H.sub.ar), 8.26 (s, 1H, H.sub.ar), 8.05 (ABq, 4H, ab=51.4 Hz, J=7.5 Hz, H.sub.ar), 7.44 (d, 1H, J=8.2 Hz, H.sub.ar), 7.22-7.185 (m, 4H, H.sub.ar), 7.14 (m, 3H, H.sub.ar), 7.05-7.02 (m, 6H, H.sub.ar), 6.99-6.95 (m, 2H, H.sub.ar), 2.58 (t, 4H, J=7.6 Hz, CH.sub.2), 1.57 (m, 4H, CH.sub.2), 1.29 (m, 12H, CH.sub.2), 0.87 (t, 6H, J=5.8 Hz, CH.sub.3).

(24) .sup.13C NMR (THF-d.sub.8, 100 MHz): =164.18; 157.44; 156.82; 155.00; 154.36; 153.83; 149.08; 147.92; 144.78; 143.26; 142.85; 142.50; 132.98; 132.25; 131.33; 130.91; 130.40; 130.11; 129.43; 129.16; 125.66; 125.49; 124.25; 124.15; 123.50; 121.47; 116.74; 105.05; 64.73; 36.80; 33.12; 32.96; 31.05; 30.50; 23.90; 14.83.

(25) II. Synthesis of the DJ214 Dye.

II.1. 5-(7-(6-(diphenylamino)-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)furan-2-carbaldehyde [DJ210]

(26) ##STR00013##

(27) In an argon atmosphere, 4,4-dioctyl,NN-diphenyl-4H-indeno[1,2-b]thiophen-6-amine (650 mg, 0.98 mmol) was dissolved in distilled THF (30 mL) after which n-BuLi (0.43 mL, 1.01 mmol) was added at 78 C. The solution was left under agitation for 1 h at 50 C. before adding a solution of Me.sub.3SnCl (1.01 mL, 1.01 mmol) in n-hexane at 78 C. After return to ambient temperature, the solution was left under agitation for 2 h. The reaction was stopped with water and the organic phase was extracted with n-hexane, dried over Na.sub.2SO.sub.4, filtered and concentrated in vacuo. The resulting oil was subjected without further purification to Stille coupling with 4-bromo-7-(4-formylbenzyl)-2,1,3-benzothiadiazole (2433 mg, 0.78 mmol). The stannic product was placed under an argon atmosphere with Pd.sub.2dba.sub.3 (18 mg, 20 mol, 2 mol %) and P(o-tolyl).sub.3 (12 mg, 40 mol). The products were dissolved in anhydrous toluene (20 mL) and placed under reflux for 12 h. The mixture was then poured into HCl (2 M). The organic phase was extracted with diethyl ether (Et.sub.2O), washed with HCl (2 M), dried over Na.sub.2SO.sub.4 and concentrated. The crude solid was purified by silica gel chromatography eluting with cyclohexane/DCM: 6:4 (v/v) whereby a red solid was obtained (490 mg, 0.55 mmol, 70.0%).

(28) .sup.1H NMR (CDCl.sub.3, 400 MHz): =9.72 (s, 1H, CHO), 8.10 (s, 1H, H.sub.ar), 8.08 (ABq, 2H, ab=135.9 Hz, 1=7.8 Hz, H.sub.ar), 7.65 (ABq, 2H, ab=175.7 Hz, J=3.7 Hz, H.sub.ar), 7.37 (d, 1H, J=8.2 Hz), 7.25-7.18 (m, 5H, H.sub.ar), 7.10-7.05 (m, 4H, H.sub.ar), 7.09 (ABq, 8H, ab=42.0 Hz, J=8.4 Hz), 7.02-6.96 (m, 3H, H.sub.ar), 2.55 (t, 4H, J=7.3 Hz, CH.sub.2), 1.63-1.53 (m, 4H, CH.sub.2), 1.38-1.25 (m, 12H, CH.sub.2), 0.87 (t, 6H, J=6.8 Hz, CH.sub.3).

(29) .sup.13C NMR (CDCl.sub.3, 100 MHz): =177.25; 155.99; 155.45; 152.19; 151.80; 147.53; 146.60; 144.31; 141.62; 141.44; 140.76; 131.29; 129.19; 128.29; 127.84; 126.47; 124.64; 124.50; 124.30; 124.12; 123.92; 123.63; 122.97; 122.85; 121.98; 120.37; 119.11; 118.83; 113.88; 63.31; 35.54; 31.72; 31.38; 29.12; 22.60; 14.08.

II.2. 2-cyano-3-(5-(7-(6-(diphenylamino)-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)furan-2-yl)acrylic Acid [DJ214]

(30) ##STR00014##

(31) In an argon atmosphere, 5-(7-(6-(diphenylamino)-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)furan-2-carbaldehyde [DJ210] (470 mg, 0.52 mmol) and cyanoacetic acid (225 mg, 2.65 mmol, 5 eq.) were dissolved in a mixture of acetonitrile (60 mL) and chloroform (40 mL). A catalytic amount of piperidine was added and the solution placed under reflux for 3 h. The solvent was removed under reduced pressure and the remaining solid was dissolved in chloroform. The organic phase was washed with a 2M solution of HCl, dried over Na.sub.2SO.sub.4 and concentrated. The crude solid was purified by silica gel chromatography eluting first with DCM, then DCM/MeOH: 95:5 (v/v) and finally DCM/MeOH/Acetic acid: 90:5:5 (v/v), after which the corresponding dye was obtained in the form of a dark purple solid (472 mg, 0.49 mmol, 93.0%).

(32) .sup.1H NMR (THF-d.sub.8, 400 MHz): =8.40-8.20 (m broad, 2H, H.sub.ar), 7.09 (s broad, 2H, H.sub.ar), 7.90 (s broad, 1H, H.sub.ar), 7.42 (s broad, 2H, H.sub.ar), 7.30-7.15 (m, 9H, H.sub.ar), 7.15-6.95 (m, 11H, H.sub.ar), 2.58 (t, 4H, J=7.4 Hz, CH.sub.2), 1.66-1.56 (m, 4H, CH.sub.2), 1.43-1.27 (m, 12H, CH.sub.2), 0.90 (t, 6H, J=6.7 Hz, CH.sub.3).

(33) .sup.13C NMR (THF-d.sub.8, 100 MHz): =156.08; 155.47; 154.97; 15.85; 151.34; 148.57; 147.66; 146.61; 144.18; 141.87; 141.12; 136.76; 131.54; 129.02; 128.08; 127.81; 126.46; 124.39; 124.14; 122.82; 122.78; 122.02; 120.23; 118.87; 115.99; 114.74; 63.28; 35.40; 31.71; 31.55; 29.09; 22.49; 13.43.

(34) III. Synthesis of the YKP89 Dye

III.1. 4,4-bis(4-hexylphenyl)-N,N-bis(4-methoxyphenyl)-4H-indeno[1,2-b]thiophen-6-amine [YKC4P85]

(35) ##STR00015##

(36) In an argon atmosphere, Pd.sub.2dba.sub.3 (3.20 mg, 3.50 mol) and tri-tert-butylphosphine tetrafluoroborate (2.03 mg, 7.0 mol) were dissolved in anhydrous toluene (5 mL). After agitation for 15 min, a solution of 6-bromo-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophene (200 mg, 349.9 mol) and 4,4-dimethoxydiphenylamine (88.2 mg, 384.8 mol) in anhydrous toluene (10 mL) was added. Potassium tert-butoxide (129.5 mg, 1.15 mmol, 3.3 eq.) was added and the resulting mixture agitated for 30 min at ambient temperature before being placed under reflux for 48 h. The mixture was then filtered through Celite and poured into HCl (2 M). The organic phase was extracted with DCM, washed with water, dried over Na.sub.2SO.sub.4 and concentrated. The crude oil was purified by silica gel chromatography eluting with n-hexane/DCM: 9:1 (v/v), whereby a pale yellow oil was obtained (230 mg, 319.4 mol, 91.3%).

(37) .sup.1H NMR ((CD.sub.3).sub.2CO.sub.3 400 MHz): =7.41 (d, 1H, J=4.9 Hz, H.sub.ar), 7.37 (d, 1H, J=8.2 Hz, H.sub.ar), 7.12-7.06 (m, 10H, H.sub.ar), 7.01 (m, 4H, H.sub.ar), 6.88 (m, 4H, H.sub.ar), 6.98 (m, 7H, H.sub.ar), 6.81 (d d, 1H, J=2.1 Hz, J=8.2 Hz, H.sub.ar), 3.80 (s, 6H, OCH.sub.2), 2.58 (t, 4H, CH.sub.2), 1.60 (m, 4H, CH.sub.2), 1.33 (m, 12H, CH.sub.2), 0.89 (t, 6H, CH.sub.3).

(38) .sup.13C NMR ((CD.sub.3).sub.2CO.sub.3 100 MHz): =156.05; 154.99; 154.68; 146.99; 142.24; 141.16; 140.92; 129.99; 128.17; 127.66; 126.81; 126.13; 123.30; 119.54; 114.66; 62.74; 54.85; 35.17; 31.54; 31.36; 22.37; 13.45.

III.2. 5-(7-(6-(bis(4-methoxyphenyl)amino)-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)furan-2-carbaldehyde [YKC4P86]

(39) ##STR00016##

(40) In an argon atmosphere, 4,4-bis(4-hexylphenyl)-N,N-bis(4-methoxyphenyl)-4H-indeno[1,2-b]thiophen-6-amine [YKC4P85] (200 mg, 0.28 mmol) was dissolved in distilled THF (15 mL). After bringing the solution to 78 C., n-BuLi (213 L, 319 mol, 1.15 eq.) was added. The solution was left under agitation for 1 h at 78 C. before adding a solution of Me.sub.3SnCl (417 L, 417 mol, 1.5 eq.) in n-hexane at 78 C. After return to ambient temperature, the solution is left under agitation for 2 h. The reaction was stopped with saturated ammonium chloride solution. The organic phase was extracted with n-hexane, washed with water, dried over Na.sub.2SO.sub.4, filtered and concentrated in vacuo. The resulting oil was subjected without further purification to Stille coupling with 5-(7-bromobenzo[c][1,2,5]thiadiazol-4-yl)furan-2-carbaldehyde (69 mg, 222 mol, 0.8 eq.). The stannic product was placed under an argon atmosphere with Pd.sub.2dba.sub.3 (5.1 mg, 5.56 mol, 2 mol %) and P(o-tolyl).sub.3 (3.37 mg, 11.11 mol, 4 mol %). The products were dissolved in anhydrous toluene (20 mL) and placed under reflux for 24 h. The mixture was then poured into HCl (2 M). The organic phase was extracted with DCM, washed with water, dried over Na.sub.2SO.sub.4 and concentrated. The crude solid was purified by silica gel chromatography eluting with DCM/n-hexane: 6:4 (v/v), whereby a dark purple solid of aldehyde type was obtained (199 mg, 209 mol, 94.4%).

(41) .sup.1H NMR (CD.sub.2Cl.sub.2, 200 MHz): =9.69 (s, 1H, CHO), 8.13 (s, 1H, H.sub.ar), 8.07 (ABq, 2H, ab=58.4 Hz, J=8.1 Hz, H.sub.ar), 7.64 (ABq, 2H, ab=84.0 Hz, J=3.5 Hz, H.sub.ar), 7.32 (d, 2H, J=8.2 Hz, H.sub.ar), 7.15-6.99 (m, 13H, H.sub.ar), 6.80 (m, 5H, H.sub.ar), 7.08-6.98 (m, 12H, H.sub.ar), 3.78 (S, 6H, OCH.sub.3), 2.56 (t, 4H, J=7.5 Hz, CH.sub.2), 1.54 (m, 4H, CH.sub.2), 1.30 (m, 12H, CH.sub.2), 0.87 (t, 6H, J=6.7 Hz, CH.sub.3).

(42) .sup.13C NMR (CD.sub.2Cl.sub.2, 50 MHz): =177.74; 156.71; 155.86; 152.53; 148.43; 145.04; 142.49; 142.33; 141.28; 141.00; 129.80; 129.48; 128.96; 128.37; 127.12; 126.91; 124.97; 124.49; 120.93; 120.15; 119.74; 119.27; 115.23; 114.36; 63.84; 56.07; 36.12; 32.40; 32.20; 29.78; 23.28; 14.54.

III.3. 3-(5-(7-(6-(bis(4-methoxyphenyl)amino)-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)furan-2-yl)-2-cyanoacrylic Acid [YKP89]

(43) ##STR00017##

(44) In an argon atmosphere, 5-(7-(6-(bis(4-methoxyphenyl)amino)-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)furan-2-carbaldehyde [YKC4P86] (180 mg, 190 mol) and cyanoacetic acid (80 mg, 950 mol, 5 eq.) were dissolved in a mixture of acetonitrile (9 mL) and chloroform (9 mL). A catalytic amount of piperidine was added and the solution placed under reflux for 3 h. The solvent was removed under reduced pressure and the remaining solid was dissolved in chloroform. The organic phase was washed with a solution of HCl (2 M), dried over Na.sub.2SO.sub.4 and concentrated. The crude solid was purified by silica gel chromatography eluting first with DCM, then DCM/methanol (MeOH): 95:5 (v/v) and finally with DCM/MeOH/Acetic acid: 90:5:5 (v/v), whereby the corresponding dye is obtained in the form of a dark purple solid (179.3 mg, 177 mol, 92.7%).

(45) .sup.1H NMR (THF-d.sub.8, 400 MHz): =8.26 (s, 1H, H.sub.ar), 8.25 (ABq, 2H, ab=88.7 Hz, J=7.7 Hz, H.sub.ar), 8.04 (s, 1H, H.sub.ar), 7.70 (ABq, 2H, ab=184.3 Hz, J=3.6 Hz, H.sub.ar), 7.36 (d, 1H, 1=8.3 Hz, H.sub.ar), 7.13 (m, 3H, H.sub.ar), 7.09 (d, 1H, J=2.1 Hz, H.sub.ar), 7.04-6.97 (m, 7H, H.sub.ar), 6.79 (m, 4H, H.sub.ar), 3.75 (S, 6H, H.sub.ar), 2.55 (t, 4H, J=7.9 Hz, CH.sub.2), 1.57 (m, 4H, CH.sub.2), 1.29 (m, 12H, CH.sub.2), 0.87 (t, 6H, J=6.5 Hz, CH.sub.3).

(46) .sup.13C NMR (THF-d.sub.8, 100 MHz): =190.60; 188.79; 175.94; 156.24; 155.35; 152.63; 152.37; 151.51; 148.49; 147.78; 142.11; 141.01; 140.73; 139.77; 139.71; 133.58; 128.00; 127.79; 126.19; 124.52; 124.29; 123.99; 120.00; 119.62; 118.99; 118.67; 114.67; 114.39; 63.22; 54.59; 35.43; 31.74; 31.60; 29.67; 29.14; 22.52; 13.45.

(47) IV. Synthesis of the YKP137 Dye.

IV.1. N,N-bis(4-(hexyloxy)phenyl)-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophen-6-amine [YKP131]

(48) ##STR00018##

(49) In an argon atmosphere, Pd.sub.2dba.sub.3 (6.40 mg, 7.0 mol) and tri-tert-butylphosphine tetrafluoroborate (4.1 mg, 14.0 mol) were dissolved in anhydrous toluene (5 mL). After agitation for 15 min, a solution of 6-bromo-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophene (400 mg, 699.7 mol) and di(hexyloxyphenyl)amine (284.4 mg, 769.7 mol, 1.1 eq.) in anhydrous toluene (10 mL) was added. Potassium tert-butoxide (259.1 mg, 2.31 mmol, 3.3 eq.) was added and the resulting mixture was left under agitation for 30 min at ambient temperature before being placed under reflux for 48 h. The mixture was then filtered through Celite and poured into HCl (2 M). The organic phase was extracted with DCM, washed with water, dried over Na.sub.2SO.sub.4 and concentrated. The crude oil was purified by silica gel chromatography eluting with n-hexane/DCM: 9:1 (v/v), whereby a pale yellow oil was obtained (353 mg, 410 mol, 58.7%).

(50) .sup.1H NMR (CDCl.sub.3, 400 MHz): =7.42 (d, 1H, J=4.9 Hz, H.sub.ar), 7.38 (d, 1H, J=8.2 Hz, H.sub.ar), 7.13-7.07 (m, 10H, H.sub.ar), 7.01 (m, 4H, H.sub.ar), 6.88 (m, 4H, H.sub.ar), 6.98 (m, 7H, H.sub.ar), 6.82 (d d, 1H, J=2.1 Hz, J=8.2 Hz, H.sub.ar), 4.00 (t, 4H, J=6.5 Hz, OCH.sub.2), 2.59 (t, 4H, J=7.6 Hz, CH.sub.2), 1.80 (m, 4H, CH.sub.2), 1.62 (m, 4H, CH.sub.2), 1.52 (m, 4H, CH.sub.2), 1.36 (m, 20H, CH.sub.2), 0.9 (d t, 12H, CH.sub.3).

(51) .sup.13C NMR (CDCl.sub.3, 100 MHz): =157.02; 156.45; 156.13; 148.51; 143.73; 142.61; 142.27; 131.40; 129.63; 129.14; 128.23; 127.58; 124.77; 121.14; 121.10; 120.99; 116.72; 69.38; 64.20; 36.66; 33.03; 32.94; 32.85; 27.08; 23.88; 23.85; 14.90; 14.88.

IV.2. 4-(7-(6-(bis(4-(hexyloxy)phenyl)amino)-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)benzaldehyde [YKC4P134]

(52) ##STR00019##

(53) In an argon atmosphere, N,N-bis(4-(hexyloxy)phenyl)-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophen-6-amine [YKP131] (300 mg, 348.7 mol) was dissolved in distilled THF (20 mL). After bringing the solution to 78 C., n-BuLi (287 L, 401 mol, 1.15 eq.) was added. The solution was left under agitation for 1 h at 78 C. before adding a solution of Me.sub.3SnCl (523 L, 523 mol, 1.5 eq.) in n-hexane at 78 C. After return to ambient temperature, the solution was left under agitation for 2 h. The reaction was stopped with a saturated ammonium chloride solution. The organic phase was extracted with n-hexane, washed with water, dried over Na.sub.2SO.sub.4, filtered and concentrated in vacuo. The resulting oil was subjected without further purification to Stille coupling with 4-bromo-7-(4-formylbenzyl)-2,1,3-benzothiadiazole (99 mg, 310.4 mol, 0.89 eq.). The stannic product was placed under an argon atmosphere with Pd.sub.2dba.sub.3 (6.4 mg, 7.0 mol, 2 mol %) and P(o-tolyl).sub.3 (4.2 mg, 14.0 mol, 4 mol %). The products were dissolved in anhydrous toluene (30 mL) and placed under reflux for 24 h. The mixture was then poured into HCl (2 M). The organic phase was extracted with DCM, washed with water, dried over Na.sub.2SO.sub.4 and concentrated. The crude solid was purified by silica gel chromatography eluting with DCM/n-hexane: 5:5 (v/v), whereby a purple solid of aldehyde type was obtained (275 mg, 250 mol, 80.6%).

(54) .sup.1H NMR (CD.sub.2Cl.sub.2, 400 MHz): =10.17 (s, 1H, CHO), 8.32 (s, 1H, H.sub.ar), 8.30 (d, 2H, J=8.3 Hz, H.sub.ar), 8.10 (m, 3H, H.sub.ar), 7.97 (d, 1H, J=7.6 Hz, H.sub.ar), 7.48 (d, 1H, J=8.3 Hz, H.sub.ar), 7.21-7.13 (m, 8H, H.sub.ar), 7.09 (d, 1H, J=3.1 Hz, H.sub.ar), 7.05 (m, 4H, H.sub.ar), 6.90 (m, 4H, H.sub.ar), 6.85 (dd, 1H, J=2.2 Hz, J=8.3 Hz, H.sub.ar), 4.01 (t, 4H, J=6.5 Hz, OCH.sub.2), 2.60 (t, 4H, J=7.8 Hz, CH.sub.2), 1.80 (m, 4H, CH.sub.2), 1.62 (m, 4H, CH.sub.2), 1.52 (m, 4H, CH.sub.2), 1.35 (m, 20H, CH.sub.2), 0.9 (dt, 12H, CH.sub.3).

(55) .sup.13C NMR (CD.sub.2Cl.sub.2, 100 MHz): =192.59; 156.77; 156.14; 154.58; 153.20; 148.83; 144.68; 143.84; 142.97; 142.32; 141.47; 141.31; 137.05; 131.07; 131.05; 130.69; 130.45; 130.23; 130.17; 129.28; 128.75; 127.42; 125.31; 125.07; 121.20; 120.37; 119.83; 116.28; 68.89; 36.17; 32.52; 32.43; 32.35; 26.58; 23.38; 23.33; 14.41; 14.38.

IV.3. 3-(4-(7-(6-(bis(4-(hexyloxy)phenyl)amino)-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)phenyl)-2-cyanoacrylic Acid [YKP137]

(56) ##STR00020##

(57) In an argon atmosphere, 4-(7-(6-(bis(4-(hexyloxy)phenyl)amino)-4,4-bis(4-hexylphenyl)-4H-indeno[1,2-b]thiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)benzaldehyde [YKC4P134] (275 mg, 250.3 mol) and cyanoacetic acid (213 mg, 2.5 mmol, 10 eq.) were dissolved in a mixture of acetonitrile (20 mL) and chloroform (10 mL). A catalytic amount of piperidine was added and the solution placed under reflux for 3 h. The solvent was removed under reduced pressure and the remaining solid dissolved in chloroform. The organic phase was washed with a solution of HCl (2 M), dried over Na.sub.2SO.sub.4 and concentrated. The crude solid was purified by silica gel chromatography eluting first with DCM, then with DCM/MeOH 95:5 (v/v) and finally with DCM/MeOH/Acetic acid: 90:5:5 (v/v), whereby the corresponding dye was obtained in the form of a dark purple-blue solid (252.5 mg, 217 mol, 86.5%).

(58) .sup.1H NMR (THF-d.sub.8, 400 MHz): =8.32 (m, 3H, H.sub.ar), 8.24 (s, 1H, H.sub.ar), 8.22 (m, 2H, H.sub.ar), 8.01 (ABq, 2H, ab=41.8 Hz, J=7.6 Hz, H.sub.ar), 7.36 (d, 1H, J=8.3 Hz, H.sub.ar), 7.13 (m, 4H, H.sub.ar), 7.09 (d, 1H, J=2.1 Hz, H.sub.ar), 7.03 (m, 4H, H.sub.ar), 6.97 (m, 4H, H.sub.ar), 6.81 (d, 1H, J=2.1 Hz, H.sub.ar), 6.78 (m, 4H, H.sub.ar), 3.92 (t, 4H, J=6.4 Hz, OCH.sub.2), 2.55 (t, 4H, J=7.6 Hz, CH.sub.2), 1.58 (m, 4H, CH.sub.2), 1.49 (m, 4H, CH.sub.2), 1.36-1.31 (m, 20H, CH.sub.2), 0.90 (dt, 12H, CH.sub.3).

(59) .sup.13C NMR (THF-d.sub.8, 100 MHz): =163.93; 156.64; 156.20; 154.50; 153.82; 153.33; 148.65; 144.82; 143.13; 142.40; 141.95; 141.61; 141.33; 132.44; 131.79; 130.41; 129.66; 128.95; 128.77; 127.09; 125.11; 124.89; 120.81; 120.59; 120.03; 115.88; 68.73; 64.22; 36.39; 32.70; 32.54; 30.33; 30.10; 26.75; 23.53; 23.47; 14.40.

(60) V. Optical Properties of the Dyes of the Invention

(61) To demonstrate the advantages of the dyes of the invention and in particular of the dyes DJ214, YKP88, YKP89 and YKP137 synthesized as described above, two dyes described in the literature were used as reference i.e.: the RK1 dye corresponding to 2-cyano-3(4-(7-(5-(4-(diphenyl amino)phenyl)-4-octylthiophen-2-yl)benzo[c][1,2,5] thiadiazol-4-yl)phenyl)acrylic acid of formula:

(62) ##STR00021## the RKF dye corresponding to 2-cyano-3-(4-(7-(6-(diphenylamino)-4,4-dihexyl-4H-indeno[1,2-b]thiophen-2-yl)benzo[c][1,2,5]thiadiazol-4-yl)phenyl)acrylic acid of formula:

(63) ##STR00022##

(64) It is very clearly apparent that the dyes of the invention exhibit improved absorption spectra compared with prior art dyes such as RK1 or RKF having efficiencies higher than 9.5% in combination with an iodine-based electrolyte which are among the highest in the literature.

(65) The spectra of the compounds of the invention, namely YKP137, DJ214, YKP88 and YKP89, are particularly well suited for applications to solar cells since they have spectral shift in the visible region compared with RK1 or RKF and/or have higher absorption coefficients (FIG. 2).

(66) Interestingly, the compounds DJ214 and YKP89 prove to have molar absorption coefficients higher than 40000 M.sup.1.Math.cm.sup.1. The high absorption coefficients allow the envisaging of applications with ionic liquid electrolyte and solid electrolyte configurations. In these configurations, to allow good penetration of the viscous electrolyte into the mesoporous electrode, the thickness of the mesoporous films must remain narrow and in particular narrower than 8 m. In this case, the small thickness is compensated for by a strong absorption of the dye.

(67) VI. Dyes of the Invention and Cells with Liquid Electrolyte

(68) VI.1. Material and Methods

(69) A. Preparation of Devices with Liquid Electrolyte

(70) The TiO.sub.2 films were purchased from Solaronix, then treated with TiCl.sub.4 and sintered at 500 C. for 30 min. After cooling, the electrodes were immersed in a solution containing the dyes in a mixture with deoxycholic acid (DCA) for 3 to 12 h at ambient temperature.

(71) For the counter-electrode, the FTO plates (Fluorine-doped Tin Oxide) were drilled with a micro-drill bit, washed with a 0.1 mol.Math.L.sup.1 solution of HCl in ethanol, then washed in a bath subjected to ultrasound with water and ethanol for 15 min. A counter-electrode in platinum was prepared by pouring 5 mM of chloroplatinic acid (H.sub.2PtCl.sub.6) in isopropyl alcohol under gravity onto the washed FTO plates, followed by sintering at 400 C. for 20 min under controlled atmosphere. The electrodes having adsorbed the dye were rinsed with ethanol and dried under a stream of nitrogen. The electrodes having adsorbed the dye were assembled and sealed with the counter-electrode using thermal adhesive films (Surlyn, Dupont 1702, thickness: 25 m) as polymer separators to produce sandwich-type cells. The liquid electrolyte was composed of 0.7 mol.Math.L.sup.1 of 1-propyl-3-methylimidazolium iodide, 0.03 mol.Math.L.sup.1 iodine, 0.1 mol.Math.L.sup.1 lithium iodide and 0.5 mol.Math.L.sup.1 tert-BP in a mixture of acetonitrile and valeronitrile (85:15 v/v). An electrolyte solution was inserted via a hole drilled on the counter-electrode. Finally, the holes were sealed with hot melt films and cover strip. The typically active surface area of the cell was about 0.36 cm.sup.2.

(72) B. Photovoltaic and Photoelectric Measurements

(73) Photovoltaic measurements of the DSSCs (Dye Sensitized Solar Cells) were performed on a solar simulator (AM 1.5 solar simulator) between the sample and a 450 W xenon excimer lamp. Simulated light intensity was calibrated using a reference Si solar cell equipped with a KG5 filter for global irradiance of about AM 1.5. The photovoltaic characteristics of the DSSCs were obtained by applying polarisation of external potential to the cells and measuring the generated photo-current with a Keithley source meter, 2400 model. The Incident Photon-to-Current conversion Efficiency (IPCE) was measured as a function of the wavelengths from 300 nm to 800 nm using an IPCE system specially adapted for dye-sensitized solar cells. A 75 W xenon lamp was used as light source to generate monochromatic radiation. Calibration was performed using a NIST(National Institute of Standards and Technology)-calibrated silicon photodiode as standard. The IPCE values were collected at a low chopping frequency of 4 Hz. The spectra of electric impedance were measured using an impedance analyser (Solartron 1260) at open-circuit potential under full solar illumination AM 1.5 (100 mW/cm.sup.2), over a frequency range of 0.110.sup.5 Hz. The alternating signal amplitude was 10 mV. Impedance parameters were determined by adjusting the impedance spectra using Z-plot software.

(74) VI.2. Results Obtained

(75) A. Photovoltaic Conversion Efficiencies with Liquid Electrolyte.

(76) To prove that the dyes of the invention exhibiting an improved absorption spectrum allow improvements in photovoltaic conversion efficiency, these dyes were used in sensitized solar cells employing a device of following structure: Sensitization of a TiO.sub.2 on FTO electrode with the dyes, Crimping with polymer separators and counter-electrode, and filling with liquid electrolyte containing the redox pair and more particular the redox pair I.sup./I.sub.3.sup..

(77) Table 1 below compiles the results of solar cells containing an iodine-based liquid electrolyte.

(78) The Fill Factor (FF) is the quality factor: it translates the capacity of the cell to evacuate photogenerated charges efficiently i.e. the ratio between the maximum power that can be obtained with a cell and theoretical power.

(79) TABLE-US-00001 TABLE 1 Dye 1: CDCA 10 V.sub.oc (mV) J.sub.sc (mA .Math. cm.sup.2) FF (%) (%) RK1 707 16.83 71 8.44 RKF 710 18.82 72 9.69 YKP88 706 18.96 71 9.54 YKP89 662 16.89 68 7.61 YKP137 729 18.56 70 9.38 DJ214 670 17.08 71 8.09 TiO.sub.2 thickness 14 (T/SP) + 3 (R/SP) m. Dye in CH.sub.3CN/t-BuOH, 1:1 for 15 h. Best result for 3 cells of each dye.

(80) Interestingly, it appears that some of the compounds of the invention, all examined under the same conditions, exhibit conversion efficiencies higher than the reference RK1. By means of the shifting of their absorption spectrum in the visible region they collect more photons and consequently they all allow more current (Jsc) to be generated than the reference RK1.

(81) Some of them, such as YKP88 with phenyl groups meeting the chemical structure of the invention, exhibit higher current intensities than the analogue thereof, RKF. In addition, these compounds absorb in wavelength ranges that are particularly sought after for the applications, since they are rare.

(82) Also, the combination of several dyes to sensitize the electrodes of which at least one meets the structure of the invention, allows a significant improvement in efficiencies. This is shown by the results in Tables 2 and 3 below.

(83) TABLE-US-00002 TABLE 2 (%) Dye/CDCA, J.sub.sc (%) (mean of 2 1/10 V.sub.oc (mV) (mA .Math. cm.sup.2) FF (%) (best cell) cells) RK1 724 14.54 72 7.65 7.63 RK1/ 730 15.50 71 8.10 7.96 YKP88, 1/1 YKP88 707 16.25 68 7.87 7.85 TiO.sub.2 thickness 8 (T/SP) + 4 (R/SP) m. Dye in CH.sub.3CN/t-BuOH, 1:1. Eluent with 0.5 mM dye + 5 mM CDCA for 3 h.

(84) TABLE-US-00003 TABLE 3 Dye/CDCA, J.sub.sc (%) 1/10 V.sub.oc (mV) (mA .Math. cm.sup.2) FF (%) (1 cell) YKP88 733 17.29 73 9.23 YKP88/YKP137, 8/2 743 20.17 71 10.68 YKP137 718 19.23 69 9.57 TiO.sub.2 thickness 14 (T/SP) + 3 (R/SP) m. Dye in CH.sub.3CN/t-BuOH, 1:1. Eluent with 0.5 mM dye + 5 mM CDCA for 3 h.

(85) Interestingly, when two compounds derived from the invention (Table 3) are used in combination, the conversion efficiencies reach 10.68%. This performance ranks among the 3 best at world level using an iodine-based electrolyte.

(86) B. Photovoltaic Conversion Efficiencies with Ionic Liquid Electrolyte

(87) It is known in the state of the art that cells containing liquid electrolytes have a propensity to degrade rapidly, this phenomenon often being linked to problems of leakage and evaporation of the solvent.

(88) To overcome these problems, one widely employed strategy is to use an electrolyte containing an ionic liquid. Therefore, the dyes of the invention were also used in sensitized solar cells using a device of following structure: Sensitization of a TiO.sub.2 on FTO electrode with the dyes, Crimping with polymer separators and counter-electrode, and filling with ionic liquid electrolyte containing the redox pair and more particularly the redox pair I.sup./I.sup.3.

(89) Table 4 below compiles the results of solar cells containing an iodine-based ionic liquid electrolyte.

(90) TABLE-US-00004 TABLE 4 Dye 1: CDCA 10 V.sub.oc (mV) J.sub.sc (mA .Math. cm.sup.2) FF (%) (%) RK1 651 13.81 71 6.38 RKF 670 17.50 67 7.87 YKP-88 642 17.39 66 7.36 YKP-89 585 16.98 66 6.60 YKP-137 665 14.09 60 5.65 DJ-214 609 16.51 68 6.80 TiO.sub.2 thickness 8.5 (T/SP + MC/SP) + 3 (R/SP) m. Dye in CH.sub.3CN/t-BuOH, 1:1 for 15 h. Best result for 3 cells of each dye.

(91) Interestingly, all the compounds of the invention with the exception of YKP137 exhibit conversion efficiencies higher than the reference RK1. By means of their improved capacity to collect photons over a wider range of wavelengths, all the compounds allow the generation of more current when used in a cell.

(92) The most interesting result to be pointed out is that the devices fabricated with the compounds of the invention have highly increased stability (FIG. 3). These stabilities were compared with that of RK1, the only compound to have been examined under these conditions of accelerated degradation (ISOS-L2) and which displays one of the best fatigue strengths in this cell configuration that has ever been reported in the literature.

(93) When the solar cells fabricated with a dye of the present invention were irradiated by 1000 W/m.sup.2 at 65 C. for 6900 h, they maintained more than 80% of their initial efficiency compared with only 74% for the reference dye RK1 which currently ranks among the most stable dyes in this field. The substitution of the alkyl groups (RKF) by aromatic groups (its analogue YKP88) clearly brings a beneficial effect since YKP88 displays much better stability than RKF (+9%). As for the YKP89 dye, this exhibits the best stability ever recorded under these conditions for an organic compound, with a 7% loss of efficiency in 7000 h.

(94) VII. Dyes of the Invention and Cells with Solid Electrolyte

(95) The fact that the dyes of the invention have strong molar absorption coefficients is of particular interest for the development of cells with solid electrolyte.

(96) It is possible to replace a liquid electrolyte, that has numerous disadvantages in terms of application (leakage, corrosion, evaporation), by an electrolyte of solid p-type conducting type. This is generally 2,2,7,7-tetrakis(N,N-dip-methoxypheny-amine)-9,9-spirobifluorene or Spiro-OMeTAD which is conventionally employed as p-type conductor:

(97) ##STR00023##

(98) Regarding devices with solid electrolyte, one limiting factor concerns the penetration of the electrolyte into the mesoporous oxide layer. It is extremely difficult to impregnate layers of thickness greater than 3 m with solid electrolytes. It is therefore advantageous to use organic dyes with strong absorption coefficient to allow thickness to be reduced without however losing out on light-collection efficiency.

(99) VII.1. Material and Methods

(100) Devices with solid electrolyte were fabricated with dyes of the invention and compared with a reference molecule in the field: RK1.

(101) The cell structure used was the following: FTO/dense TiO.sub.2/mesoporous TiO.sub.2(2 m)/dye/Spiro-OMeTAD/Au (Active surface area: 0.15 cm.sup.2)

(102) The procedure employed for fabrication applied the following main steps: depositing compact layers of TiO.sub.2 (250 nm) (hole-blocking) via spray pyrolysis onto etched glass/FTO substrates; depositing porous layers of TiO.sub.2 using a commercial paste of DYESOL trademark, calcining heat treatment, thickness obtained 3 m; sensitizing with dyes RK1, YKP88 or YKP137, in particular for between 5 and 24 h with 0.2 mM of dye in a mixture of tert-butanol/acetonitrile (50:50 by volume)+2 mM chenodeoxycholic acid (CDCA); sensitization: 15 h in the dark at ambient temperature+rinsing with acetonitrile (ACN); filling the pores with spiro-OMeTAD molecular glass (Merck) with 200 mg/ml spiro-OMeTAD in chlorobenzene, doped tert-BP and Li-TFSI; depositing a gold counter-electrode (a few hundred nanometres thick) via vacuum evaporation (10.sup.6 mbar).

(103) VII.2. Results Obtained

(104) Preliminary results (non-optimized) obtained in solid electrolyte configuration with the dyes of the invention i.e. YKP88 and YKP137 and with the reference RK1 are given in Table 5 below.

(105) TABLE-US-00005 TABLE 5 Dye 1: CDCA 10 V.sub.oc (mV) J.sub.sc (mA .Math. cm.sup.2) FF (%) (%) RK1 772 9.17 58 4.11 YKP88 927 9.63 50 4.50 YKP137 815 10.25 47 3.90

(106) These results again show the superiority of the dyes of the invention (YKP88 and YKP137) which, in solid electrolyte cells, provide more current (higher than 9.5 mA/cm.sup.2) and lead to obtaining equivalent or better results in terms of conversion efficiency than the reference dye (RK1).

BIBLIOGRAPHY

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