1. Ruangchai Tarsang E-mail: ruangchai.tarsang@hotmail.com Department of Chemistry, Faculty of Science, Ubon Ratchathani University Center for Organic Electronics and Alternative Energy Pure and Applied Chemistry International Conference (PACCON2013) January 24th, 2013 The Tide Resort, Bangsaen Beach, Chon Buri, Thailand Tuning the electron donating ability in the triphenylamine- based D-  -A dye with enhanced power conversion efficiency of dye-sensitized solar cells

2. Conclusions 5 Objectives 2 Computational Details 3 Results and Discussion 4 Outline of Presentation Background and Significance 1 2

3. 1.Background and Significance Dye-sensitized solar cells (DSSCs) Prof. M. Grätzel, Switzerland, 1991 Advantages : low cost materials easy to be fabricated friendly to the enviroment  still very low power conversion efficiency DSSCs  expensive raw material  complicate fabrication process  toxic gases Disadvantages : Silicon solar cell 3

4. Basic Working principle of DSSCs e- DSSCs components:  Sensitizer (Dye)  Metal Oxide layer  Electrolyte system  Electrodes - Working electrode - Counter electrode 1.Background and Significance 4 e-

5. 1.Background and Significance Classification of DSSCs Suitable sensitizer : for increasing DSSCs efficiency 1) Ruthenium complexes: 2) Organic-based dyes:  coumarins  porphyrin  indoline  ~ 11 %  ~ 5-9 % Adv. Mater. 2006, 18, 1202-1205 Coord Chem Rev. 2004, 248, 1363-1379; 5  rare material  complicate synthesis Disadvantages :

6. 3. Suitable energy levels 2. One direction of electron flow 1. Wide absocccrption range Criteria for efficient DSSCs 1.Background and Significance 6 H. Tian et al, Chem. Commun., 2007, 3741 - 374 HOMOLUMO

7. 1.Background and Significance Triphenylamine (TPA) dyes in DSSCs 7 HOMO LUMO Chem. Commun., 2006, 2245–2247 an efficient intramolecular charge separation

8. 1.Background and Significance Triphenylamine (TPA) dyes in DSSCs 8 J. Org. Chem., 2008, 73, 3791–3797 D-D-  -A Developed: modifying the molecular structure, especially the electron donor  block the charge recombination  reduce the intermolecular π–π stacking Eur. J. Org. Chem., 2012 Recently

9. 2.Objectives Organic materials for application in DSSCs To study the effect of the substituted donating group number 9 carbazole

10. 2.Objectives Organic materials for application in DSSCs 10 To study the effect of the different substituted donating group diphenylamine

11. 3.Computational Details Structural and energetic calculations of DSSCs  The ground-state geometries DFT with B3LYP/6-31G(d,p)  The excitation energy TD-DFT/CAM-B3LYP//B3LYP/6-31G(d,p)  Absorption spectra SWizard program  All the calculations were performed using the Gaussian 09 program package the Gaussian 09 program package UBUchem server Kankrao server 11

12. 4.Results and Discussion Optimal ground-state electronic structures Fig.1 Molecular (a) and Optimized (b) structures of the triphenylamine dyes 12 dihedral angle

13. Dye Dihedral angle (degree) D(2D)-DD-ππ-A TPA donor 1 - 21 - 3 TPA-20.760.93 46.80 45.62 TPA152.88 -21.591.00 44.43 47.06 TPA2 53.07 (-52.09) -22.130.6345.6545.40 TPA3 36.97 (-36.34) -21.280.6946.5243.93 TPA438.64 -20.640.97 49.51 45.03 TPA5 38.80 (-39.18) -19.910.9948.5547.94 4.Results and Discussion Optimal ground-state electronic structures 13 Table 1: Selected dihedral (in degree) of the triphenylamine dyes TPA-TPA5 Fig.1 Molecular (a) and Optimized (b) structures of the triphenylamine dyes nonplanar conformation

14. Frontier molecular orbitals 4.Results and Discussion 14 HOMO LUMO Fig.2 Molecular orbiyals surface of HOMO and LUMO orbitals of the triphenylamine dyes Increase the electron density for HOMO Tuning the electron donating ability

15. Effect of intramolecular charge transfer (ICT) 4.Results and Discussion 15 Fig.3 The density difference between the ground-state and the first excited-state of TPA, TPA1, and TPA2 dyes CT character of the first transition density difference map: (TDDFT/CAM-B3LYP/6-31G(d,p)/CPCM) Presence the electron transfer going from GS to ES satisfied

16. Absorption spectra and Electronic transitions 4.Results and Discussion 16 TPA TPA2 TPA1 Fig.4 Simulated absorption spectra of the triphe-nylamine dyes TPA-TPA5 at the CAM-B3LYP/6-31g(d,p) level in dichloromethane solution TPA TPA1 TPA2 No shifted of abs Carbazole donor  How can we change the abs of carbazole substituted group? 430

17. Absorption spectra and Electronic transitions 4.Results and Discussion 17 TPA1 TPA2 TPA3 TPA4 TPA5 Fig.4 Simulated absorption spectra of the triphe-nylamine dyes TPA-TPA5 at the CAM-B3LYP/6-31g(d,p) level in dichloromethane solution Red-shifted satisfied 435 441453

18. Absorption spectra and Electronic transitions 4.Results and Discussion Table 2. Absorption wavelength ( abs ), excitation energy (E g ), oscillator strength (  ) and electronic transition configurations of triphenylamine dyes 18 Dye abs /nm, E g /eV (  x10 -4 M -1 cm -1 )  Configuration TPA430, 2.88 (10.37) 1.4305 H  L (80%); H-1  L (14%) TPA1429, 2.89 (10.77) 1.4860 H  L (61%); H-1  L (21%) TPA2428, 2.90 (11.16) 1.5399 H  L (59%); H-2  L (25%) TPA3435, 2.85 (12.27) 1.6931 H  L (61%); H-2  L (14%) TPA4441, 2.81 (10.47) 1.4444 H  L (60%); H-1  L (25%) TPA5453, 2.74 (10.58) 1.4596 H  L (65%); H-2  L (24%) CT absorption band Red-shifted

19. Energy level (eV) 4.Results and Discussion Molecular orbitals Energy level Fig. 5. Energy diagram of HOMO and LUMO for the triphenylamine dyes, TiO 2, and the electrolyte 19 injection from the dye excited state satisfied Change the HOMO energy

20. 5.Conclusions We have analyzed effect of two different auxiliary donor groups of carbazole and diphenylamine on the ground-state structure, electronic structure as well as the absorption spectra of D-π-A organic dyes. Carbazole auxiliary donor provided the large dihedral angle between auxiliary donor and TPA donor resulting in not red-shifted of absorption wavelength. This trouble was improved by either introduction fluorine unit between carbazole and TPA groups or replaced carbazole auxiliary donor by diphenylamine group. We may conclude that TPA5 dye molecule which is the most red-shifted of absorption spectra have the potential to be employed in the DSSCs applications. 20

21. Department of Chemistry, Faculty of Science, Ubon Ratchathani University  National Nanotechnology Center:  Center for Organic Electronics and Alternative Energy,  Advisor: Asst.Prof.Dr. Siriporn Jungsuttiwong  Pure and Applied Chemistry International Conference (PACCON2013)  Financial supported: Human Resource Development in Science Project (Science Achievement Scholarship of Thailand, SAST) Acknowledgement 21