Molecular Engineering of Organic Sensitizers for Solar Cell Applications

• Published in: Journal of the American Chemical Society Vol. 128; no. 51; pp. 16701 - 16707
• Main Authors: Kim, Sanghoon, Lee, Jae Kwan, Kang, Sang Ook, Ko, Jaejung, Yum, J.-H, Fantacci, Simona, De Angelis, Filippo, Di Censo, D, Nazeeruddin, Md. K, Grätzel, Michael
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 27.12.2006; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Multidisciplinary; Exact sciences and technology; General and physical chemistry; Heterocyclic compounds; Heterocyclic compounds with o, s, se, te hetero atom and condensed derivatives; Organic chemistry; Physical Sciences; Preparations and properties; Science & Technology; PHOTOELECTROCHEMICAL CHARACTERIZATION; SEMICONDUCTOR; NANOCRYSTALLINE TIO2; DYNAMICS; ELECTRON-INJECTION; DENSITY-FUNCTIONAL THEORY; ENERGIES; HIGH-EFFICIENCY; COUMARIN DYES; EXCITED-STATES; Molecular orbital; Organic thiocyanate; Titanium IV Oxides; Organic cation; Nitrile; Visible absorption; Asymmetric molecule; Theoretical study; Guanidinium compounds; Organic iodine compounds; Thiophene derivatives; Sulfur heterocycle; Electronic structure; Electrolyte; Functionalization; Optical properties; Acetonitrile; Density functional method; Redox potential; Chemical synthesis; Anchoring; Electron donor; Sensitizer; Acrylic acid derivatives
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja066376f

Novel organic sensitizers comprising donor, electron-conducting, and anchoring groups were engineered at molecular level and synthesized. The functionalized unsymmetrical organic sensitizers 3-{5-[N,N-bis(9,9-dimethylfluorene-2-yl)phenyl]-thiophene-2-yl}-2-cyano-acrylic acid (JK-1) and 3-{5‘-[N,N-bis(9,9-dimethylfluorene-2-yl)phenyl]-2,2‘-bisthiophene-5-yl}-2-cyano-acrylic acid (JK-2), upon anchoring onto TiO2 film, exhibit unprecedented incident photon to current conversion efficiency of 91%. The photovoltaic data using an electrolyte having composition of 0.6 M M-methyl-N-butyl imidiazolium iodide, 0.04 M iodine, 0.025 M LiI, 0.05 M guanidinium thiocyanate, and 0.28 M tert-butylpyridine in a 15/85 (v/v) mixture of valeronitrile and acetonitrile revealed a short circuit photocurrent density of 14.0 ± 0.2 mA/cm2, an open circuit voltage of 753 ± 10 mV, and a fill factor of 0.76 ± 0.02, corresponding to an overall conversion efficiency of 8.01% under standard AM 1.5 sunlight. DFT/TDDFT calculations have been performed on the two organic sensitizers to gain insight into their structural, electronic, and optical properties. Our results show that the cyanoacrylic acid groups are essentially coplanar with respect to the thiophene units, reflecting the strong conjugation across the thiophene-cyanoacrylic groups. Molecular orbitals analysis confirmed the experimental assignment of redox potentials, while TDDFT calculations allowed assignment of the visible absorption bands.