The novel methyl-substituted dicyanovinyl-capped quinquethiophenes 1-3 led to highly efficient organic solar cells with power conversion efficiencies of 4.8-6.9%. X-ray analysis of single crystals and evaporated neat and blend films gave insights into the packing and morphological behavior of the novel compounds that rationalized their improved photovoltaic performance.

provide good solubility in organic solvents and processability, we attached branched alkyl substituents at the DTP-nitrogen (ethylhexyl (EH) 1 , 4 , octylnonyl (ON) 2 , 5 , hexyldecyl (HD) 3 , 6 ) and hexyl side chains to each thiophene unit in a regioregular fashion as a mimic of the well-known and frequently used regioregular poly(3-hexylthiophene). [ 26 ] Thereby, the hexyl chains were attached either at the outer ( 1 -3 ) or inner ( 4 -6 ) positions thus yielding three isomeric pairs, which only differ in the positioning of the side chains. As a result, excellent solubilities of ≥120 mg mL −1 in chloroform for molecules 5 and 6 have been obtained. First solar cell results of oligomer pair 1 and 4 have recently been published and we discovered a striking difference between the photovoltaic behavior of the two isomers. [ 16 ] Whereas the so far highest PCE of 4.8% for any DTP-based oligomer has been obtained for oligothiophene 1 and PC 61 BM in BHJSCs, isomer 4 showed a lower performance (0.8%), which we attributed to the different blend morphologies and phase separation probed by atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. [ 16 ] The detailed photovoltaic behavior, further optimization, and characterization of the photoactive layers of the whole series of soluble DTP-oligothiophenes 1 -6 is now described. Signifi cant improvement of the oligomer BHJSC performance was obtained by SVA, which was investigated by absorption spectroscopy, grazing incidence XRD (GI-XRD), and AFM. After extensive optimization, power conversion effi ciencies up to 6.1% and fi ll factors greater than 70% were achieved.

The aim of this work is to investigate the effect of incorporating an iridium complex into a π-conjugated polymer backbone on photovoltaic properties such as charge generation, power conversion efficiency and external quantum efficiency (EQE). Poly(9,9-dihexylfluorene-co-2-phenylpyridine) (1) and poly(9,9dioctylfluorene-co-tris(2-phenylpyridine) iridium (III))) (2) were synthesized using Suzuki polycondensation. Characterization was performed using NMR, UV-vis, photoluminescence, and time-resolved luminescence spectroscopy; gel permeation chromatography; elemental analysis; and photovoltaic devices. An increase in percent EQE for 2 over 1, from 1.1 to 10.3, is attributed to the formation of the triplet state in (2), and by inference, longer diffusion lengths of the triplet exciton, compared to the singlet exciton that is formed in (1).

We highlight the influence of processing conditions on polymorphism and structure formation on the mesoscale for the family of PCPDTBT polymers with branched alkyl side chains. Direct correlations of morphology to the chemical structure and to transistor device performance are established. We found that up to four different packing motifs could be realized depending on the polymer derivative and the processing conditions: amorphous, -stacked, cross-hatched and dimer-containing polymorphs. While C-and F-PCPDTBT display similar packing behavior organizing in -stacked and dimer-like structures, Si-PCPDTBT gives rise to cross-hatched structures upon simple deposition from solution. The observed differences in chain packing for C-/F-PCPDTBT versus Si-PCPDTBT are related to differences in backbone conformations and aggregation behavior in solution. The effect of polymorphism on charge transport is probed using field-effect transistors, in which both -stacked and cross-hatched polymer chain arrangements yield the highest hole mobilities. Structural and mobility simulations rationalize our experimental findings by relating mobility to distributions of electronic coupling elements between the chains.

Conjugated fluorene-alt-pyridine and fluorene-alt-thiophene polymers containing phosphorescent iridium complexes have been synthesized. Exchanging the 2,5-linked pyridine group with the 3,4-linked thiophene group resulted in a blue shift in the absorption and emission spectra of the conjugated polymers. Upon incorporation of the thienyl unit, phosphorescent quantum yields of films increased from 0.05 to 0.20 and electrophosphorescent external quantum efficiencies increased from 0.32 to 0.84%. These results are attributed to raising the triplet energy of the main chain polymer, with respect to the Ir phosphor, thereby reducing quenching of the phosphor by the main chain.