A faux hawk fullerene with PCBM-like properties

Reaction of C60, C6F5CF2I, and SnH(n-Bu)3 produced, among other unidentified fullerene derivatives, the two new compounds 1,9-C60(CF2C6F5)H (1) and 1,9-C60(cyclo-CF2(2-C6F4)) (2). The highest isolated yield of 1 was 35% based on C60. Depending on the reaction conditions, the relative amounts of 1 and 2 generated in situ were as high as 85% and 71%, respectively, based on HPLC peak integration and summing over all fullerene species present other than unreacted C60. Compound 1 is thermally stable in 1,2-dichlorobenzene (oDCB) at 160 °C but was rapidly converted to 2 upon addition of Sn2(n-Bu)6 at this temperature. In contrast, complete conversion of 1 to 2 occurred within minutes, or hours, at 25 °C in 90/10 (v/v) PhCN/C6D6 by addition of stoichiometric, or sub-stoichiometric, amounts of proton sponge (PS) or cobaltocene (CoCp2). DFT calculations indicate that when 1 is deprotonated, the anion C60(CF2C6F5)− can undergo facile intramolecular SNAr annulation to form 2 with concomitant loss of F−. To our knowledge this is the first observation of a fullerene-cage carbanion acting as an SNAr nucleophile towards an aromatic C–F bond. The gas-phase electron affinity (EA) of 2 was determined to be 2.805(10) eV by low-temperature PES, higher by 0.12(1) eV than the EA of C60 and higher by 0.18(1) eV than the EA of phenyl-C61-butyric acid methyl ester (PCBM). In contrast, the relative E1/2(0/−) values of 2 and C60, −0.01(1) and 0.00(1) V, respectively, are virtually the same (on this scale, and under the same conditions, the E1/2(0/−) of PCBM is −0.09 V). Time-resolved microwave conductivity charge-carrier yield × mobility values for organic photovoltaic active-layer-type blends of 2 and poly-3-hexylthiophene (P3HT) were comparable to those for equimolar blends of PCBM and P3HT. The structure of solvent-free crystals of 2 was determined by single-crystal X-ray diffraction. The number of nearest-neighbor fullerene–fullerene interactions with centroid⋯centroid (⊙⋯⊙) distances of ≤10.34 Å is significantly greater, and the average ⊙⋯⊙ distance is shorter, for 2 (10 nearest neighbors; ave. ⊙⋯⊙ distance = 10.09 Å) than for solvent-free crystals of PCBM (7 nearest neighbors; ave. ⊙⋯⊙ distance = 10.17 Å). Finally, the thermal stability of 2 was found to be far greater than that of PCBM

Origin of line broadening in the electronic absorption spectra of conjugated polymers: Three-pulse-echo studies of MEH-PPV in toluene

Integrated three-pulse stimulated echo peak shift data are compared for N,N-bis-dimethylphenyl-1-2,4,6,8-perylenetetracarbonyl diamide and poly[2-(2'-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] (MEH-PPV) in toluene solvent. These two molecules represent a model probe of solvation dynamics and a prototypical soluble, electroluminescent conjugated polymer, respectively. The results indicate that it is inappropriate to describe the linear absorption spectrum of MEH-PPV as being primarily inhomogeneously broadened. Conformational disorder along the polymer backbone gives rise to an ensemble of polyene electronic oscillators that are strongly coupled to each other. As a consequence, fluctuations in the electronic energy gap on a time-scale of 50-fs derive primarily from bath-mediated exciton scattering. The data reported here provide an explanation for the broad, structureless electronic absorption of MEH-PPV. This interpretation provides a valuable insight into the nature of the initial photoexcited state, and the efficient population of the emissive state

Hybrid organic-inorganic solar cells

In this special section of the Journal of Photonics for Energy, there is a focus on some of the science and technology of a range of different hybrid organic-inorganic solar cells. Prior to 1991 there were many significant scientific research reports of hybrid organic-inorganic solar cells; finally, however, it wasn’t until the dye-sensitized solar cell entered the league table of certified research cell efficiencies that this area experienced an explosion of research activity

Quantitative Transient Absorption Measurements of Polaron Yield and Absorption Coefficient in Neat Conjugated Polymers

Transient absorption methods are crucial for probing photogenerated polaron dynamics in conjugated polymers but are usually limited to qualitative studies because the polaron absorption coefficient is unknown. Herein, we quantify polaron absorption coefficients by exploiting the parasitic exciton–polaron quenching process, which appears in transient absorption experiments as a decrease in polaron yield at high fluence. We modulate the charge density in neat polymer films and measure the exciton–polaron quenching rate constant and dopant density via time-resolved photoluminescence. Using these parameters, we fit relative yield–fluence curves obtained from transient absorption, quantifying the yield and absorption coefficient of the polarons. We use time-resolved microwave conductivity as the transient probe and present results for the GHz mobility and polaron yield in films of three common conjugated polymers that are consistent with previous reports where they exist. These experiments demonstrate a new, generally accessible spectroscopic method for quantitative study of polaron dynamics in conjugated polymers

Revealing the dynamics of charge carriers in polymer:fullerene blends using photoinduced time-resolved microwave conductivity

During the past decade, time-resolved microwave conductivity (TRMC) has evolved to an established, powerful technique to study photoactive layers. With this feature paper, we aim to fulfill two goals: (1) give a full description of the photoinduced TRMC technique, including experimental details and data analysis, and discuss to what extent the TRMC technique differs from more conventional DC techniques and (2) illustrate the potential of this technique for probing charge carrier dynamics in photoactive materials. For these reasons recent studies on conjugated polymer:fullerene blends will be presented and discussed. The findings from these studies have advanced the insight into the mechanism of charge carrier generation and decay in polymer:fullerene blends, which allows us to improve the efficiency of organic photovoltaic cells based on this active layer architecture. In short, it is shown how the TRMC technique can be used as a versatile method to screen the potential of new photovoltaic materials.19 page(s

Influence Of Squaraine Aggregation On Short-Circuit Current And Device Efficiency

Linear absorption measurements, current-voltage characteristics, and time-resolved microwave conductivity measurements were utilized to investigate the impact of molecular aggregation of a novel donor material on photovoltaic device efficiency. We report efficiencies of 2.4+/-0.3% and explain the increase in short-circuit current and efficiency as a function of the increased aggregation. © 2012 IEEE