Efficient bulk heterojunction solar cells based on solution processed small molecules based on the same benzo[1,2-b:4, 5-b']thiophene unit as core donor and different terminal units.

We report the synthesis, characterization, and optical and electrochemical of properties of two novel molecules DRT3-BDT (1) and DTT3-BDT (2), comprising the same BDT central core (donor) and different end capped acceptor units, i.e. rhodanine with ethyl hexyl and thiazolidione with ethylhexyl, respectively, linked via an alkyl-substituted terthiophene (3 T) π-conjugation bridge. The electrochemical properties of these small molecules indicate that their energy levels are compatible with energy levels of PC71BM for efficient exciton dissociation. These molecules have been used as electron donors along with PC71BM as an electron acceptor, for the fabrication of solution processed "small molecule" bulk heterojunction (BHJ) solar cells (smOPV). The device prepared from optimized 1:PC71BM(1:1) processed cast from DIO (3%v)/CF solvent exhibited a power conversion efficiency of 6.76% with Jsc = 11.92 mA cm(-2), Voc = 0.90 and FF = 0.63. The device with 2:PC71BM under the same conditions showed a lower PCE of 5.25% with Jsc = 10.52 mA cm(-2), Voc = 0.86 and FF = 0.56. The AFM, TEM and PL quenching measurements revealed that the high Jsc is a result of the appropriate morphology and exciton dissociation. The performances were compared for the devices based on two small molecules. The higher Jsc for device 1 was attributed to its better nanoscale phase separation, smooth surface and higher carrier mobility in the 1:PC71BM blend film. Moreover, the higher value of FF for the 1:PC71BM based device was ascribed to a good balance between the electron and hole mobilities.

Synthesis and characterization of donor-π-acceptor-based porphyrin sensitizers: potential application of dye-sensitized solar cells.

New porphyrin sensitizers based on donor-π-acceptor (D-π-A) approach have been designed, synthesized, characterized by various spectroscopic techniques and their photovoltaic properties explored. N,N'-Diphenylamine acts as donor, the porphyrin is the π-spacer, and either carboxylic acid or cyanoacryclic acid acts as acceptor. All compounds were characterized by using (1)H NMR spectroscopy, ESI-MS, UV-visible emission spectroscopies as well as electrochemical methods. The presence of aromatic groups between porphyrin π-plane and acceptor group push the absorption of both Soret and Q-bands of porphyrin towards the red region. The electrochemical properties suggests that LUMO of these sensitizers above the TiO2 conduction band. Finally, the device was fabricated using liquid redox electrolyte (I(-)/I3(-)) and its efficiency was compared with that of a leading sensitizer.

Axial-bonding heterotrimers based on tetrapyrrolic rings: synthesis, characterization, and redox and photophysical properties.

We prepared two heterooligomeric arrays based on free base/metalloporphyrins at axial positions and a metalloid phthalocyanine as a basal scaffolding unit by using the axial-bonding capabilities as well as the known oxophilicity of dihydroxytin(IV) phthalocyanine. Both heterotrimers were completely characterized by elemental analysis, MALDI-TOF MS, and 1H NMR (one- and two-dimensional), UV/Vis, and fluorescence spectroscopy as well as cyclic voltammetry. The ground-state properties indicate that there is minimal pi-pi interaction between the macrocyclic units. The excited-state properties show that there is electronic energy transfer competing with photoinduced electron transfer from the singlet state of the axial porphyrin to the central metalloid phthalocyanine and a photoinduced electron transfer from the ground state of the axial porphyrin to the singlet state of the central metalloid phthalocyanine.