This thesis concentrates on the development and synthesis of new metal-containing phthalocyanine and metal-free organic dyes for dye-sensitized solar cells (DSC). In this thesis attempts have been made to cover a broad region of visible light through the synthesis of three different dye families. The N719 is the common dye was used as a sensitizer in DSC devices, which absorbs at 450-600 nm, while in this thesis were synthesized and developed three new types of dyes to work either side of N719 absorb light at (400-450) nm for yellow and red single or di-linker dyes, cyanine and phthalocyanine dyes which absorb higher than 600 nm.
This thesis consists of six chapters. Chapter one includes a short history and introduction to dye-sensitized solar cells with a description of triarylamine,phthalocyanine and cyanine dyes, which are related to this thesis work.
The second chapter describes the experimental techniques which have been used to synthesize the target compounds and then tested them in DSC devices.
Chapter three describes the synthesis new triphenylamine dyes based on the donor-π- acceptor (D-π-A) concept. In this chapter three new dyes were synthesized; single-linker yellow dye 4-[2-( 4-diphenylamino-phenyl)-vinyl]-benzoic acid (5), dilinker yellow dye 5-[2-(4-diphenylamino-phenyl)-vinyl]-isophthalic acid (14) and dilinker red dye (2Z, 2'Z)-3, 3'-(5-((E)-4-(diphenylamino) styryl)-1, 3-phenylene) bis (2-cyanoacrylic acid) (12). In addition, the single-linker red dye 2-cyano-3-{4-[2-(4- diphenylamino-phenyl) vinyl]-phenyl}-acrylic acid (3) was re-synthesized. These dyes included a triphenylamine donor moiety, a π-bridge (linker) and one or two carboxylic or cyanoacrylic acids as the acceptor moiety. During the synthesis of these triphenylamine dyes diphenyl-(4-vinyl-phenyl)-amine (1) was the main starting material which was used to synthesize all the triphenylamine dyes. This was synthesized by a Wittig reaction of 4-(N, N-diphenylamino)-benzaldehyde with potassium tert-butoxide and methyl triphenyl phosphonium iodide in distilled THF. The purpose was to compare single-linker and di-linker dyes to try to improve their DSC photovoltaic performance. In addition, these dyes were co-sensitized with other dyes to capture more light and to try to enhance the DSC performance. Single-linker red dye shows the highest overall conversion efficiency of 3.4%, while the other dyes ranged from 1.2-2. 7%. Dye (5) shows the best results after co-sensitizing with N719 dye (7.5%). The stability of new single-linker yellow dye 4-[2-(4-diphenylaminophenyl)-vinyl]-benzoic acid (5) was investigated, showed excellent stability during thermal and light soaking.
Chapter four describes the synthesis of cyanine dyes, which are the second type of dyes synthesized. The cyanine dyes 3-(2-((E)-2-((E)-3-((E)-2-(1-(2-carboxyethyl)- 3 ,3-dimethylindolin-2-ylidene) ethylidene )-2-chlorocyclohex-1-en-l-yl) vinyl)-3, 3- dimethyl-3 H-indol-1-ium-1-yl )propanoate (34), 3-(2-( (E)-2-( (E)-3-( (E)-2-(3-(2- carboxyethyl)-1, l-dimethyl-1 H-benzo[ e ]indol-2(3H)-ylidene) ethylidene)-2- chlorocyclohex-l-en-l-yl)vinyl)-1, 1-dimethyl-lH-benzo[ e]indol-3-ium-3- yl)propanoate (35) and cyanine derivatives 3-(2-((E)-2-((E)-2-chloro-3-((E)-2-(lethyl-3,3-dimethyl-1 H-benzo[g]indol-2(3H)-ylidene )ethylidene) cyclohex-l-en-lyl)vinyl)-1, l-dimethyl-lH-benzo[ e]indol-3(2H)-yl)propanoic acid compound (37) and 3-(2-carboxyethyl)-2-( 4-( diphenylamino )styryl)-1, 1-dimethyl-1 H-benzo[ e ]indol3-ium (38) were synthesized by condensation reaction of heterocyclic groups 1-carboxyethyl-2, 3, 3-trimethylindolenium iodide (29), l-carboxyethyl-2, 3, 3- trimethyl-1H-benzo [ 0]-indolium iodide (30), (E)-2-chloro-3- (hydroxymethylene)cyclohex-1-enecarbaldehyde (33), l-ethyl-2, 3, 3- trimethylindolenium iodide and 4-(N, N-diphenylamino)-benzaldehyde as discussed earlier. The cyanine dyes (34), (35) and (37) absorb near the infrared light (NIR) at around 800 nm, while (38) absorbs at around 550 nm. These compounds show over all conversion efficiency from 0.05-0.25%. In addition the influence of co-adsorbents as additives to improve the photovoltaic parameters and the film thickness of semiconductor, are reported in this chapter.
Chapter five describes the synthesis of phthalocyanine dyes. The new unsymmetrical phthalocyanine 2, 3-di (4-benzoic acid)-7² ,12² ,17² -hexa (2, 6-diphenylphenoxy)- tribenzo-5, 10, 15, 20-tetrazaprophyrin zinc (24) and the symmetrical phthalocyanine 2², 7², 12², 17² octa (2, 6-diphenylphenoxy)-tetrabenzo-5, 10, 15, 20-tetrazaprophyrin zinc (26) were successfully prepared. Many attempts were also made to synthesize 2, 3-di ( 4-benzoic acid)-7², 12²,17² -hexa (2, 6-diphenylphenoxy)-tetrabenzo-5, 10, 15,20-tetrazaprophyrin zinc (28) but without success. Purity is the main problem for phthalocyanine dyes, and this chapter successfully developed a new method to resolve the purity problem was developed. The phthalocyanine dye (24) absorbs light in the near the infrared region (NIR) around 708 nm, and shows over all conversion efficiency of up to 0.7%.
Finally, chapter six includes conclusions of the thesis work, and suggestions for future work.