. (2017) High operational and environmental stability of high-mobility conjugated polymer fieldeffect transistors achieved through the use of molecular additives. Nature Materials, 16 (3 Copies of full items can be used for personal research or study, educational, or not-for profit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. challenge is now to achieve the required device uniformity for large-area 46 applications, such as displays. With conjugated polymers that show high field-effect 47

Conventional semiconducting polymer synthesis typically involves transition metal-mediated coupling reactions that link aromatic units with single bonds along the backbone. Rotation around these bonds contributes to conformational and energetic disorder and therefore potentially limits charge delocalisation, whereas the use of transition metals presents difficulties for sustainability and application in biological environments. Here we show that a simple aldol condensation reaction can prepare polymers where double bonds lock-in a rigid backbone conformation, thus eliminating free rotation along the conjugated backbone. This polymerisation route requires neither organometallic monomers nor transition metal catalysts and offers a reliable design strategy to facilitate delocalisation of frontier molecular orbitals, elimination of energetic disorder arising from rotational torsion and allowing closer interchain electronic coupling. These characteristics are desirable for high charge carrier mobilities. Our polymers with a high electron affinity display long wavelength NIR absorption with air stable electron transport in solution processed organic thin film transistors.

nonradiative energy loss mechanisms is highly desirable. We note that nonradiative recombination processes can also occur, for instance, because of poor contacts at the electrodes and, in the case of nongeminate recombination, not only via singlet 1 CT states but also via triplet 3 CT states [30] (a topic of future studies in our group).Up to now, the theoretical investigations of the NR recombination process in organic solar cells have been conducted under the Born-Oppenheimer (BO) approximation. [31][32][33][34][35] Thus, the possible impact of nonadiabatic vibronic coupling due to the breakdown of the BO approximation (for instance, in particular, when the energy difference between the initial and final states is small) has been neglected. We note that the nonradiative recombination via nonadiabatic coupling (NAC) was initially investigated in inorganic semiconductors in the early 1950s; there, it was found to play an important role in reducing the number of photogenerated carriers, suppressing luminescence, and decreasing the carrier lifetimes. [36][37][38] In molecular systems, the NR transition between two excited states or between an excited state and the ground state (with the same spin multiplicity) due to nonadiabatic coupling, is referred to as internal conversion. [39] In the case of organic emitters, the theoretical studies of Shuai and co-workers have demonstrated that internal conversion significantly limits the fluorescence quantum yields. [40,41] Compared to the energies (usually in the range 2.0-4.0 eV) of the first excited states in organic emitters, the 1 CT 1 -state energies are generally much lower in organic solar cells, on the order of 0.5-1.7 eV. [22,23,29,42] Thus, the nonadiabatic coupling between the 1 CT 1 state and the ground state can be expected to be large and it becomes important to evaluate the role that nonadiabatic coupling can play in the NR recombination of 1 CT 1 states at donor-acceptor interfaces. We emphasize that the NR recombination rates of interfacial 1 CT 1 states are difficult to measure experimentally since the distribution of the 1 CT 1 states in transient experiments is far from equilibrium. [43,44] Here, we have chosen the pentacene-C 60 interface as a re presentative system to study the factors determining the NR recombination rates in the context of OPV applications, since a large number of data are available from earlier experimental and theoretical studies. [31,[45][46][47][48] As the recombination process is expected to depend on the local D-A interface geometry, we have considered both edge-on and face-on interfacial orientations of the pentacene molecules relative to C 60 . Also, we consider two different packing modes of the pentacene molecules: (i) a herringbone-type packing (referred to as [P:herringbone] hereafter) directly taken from the pentacene crystal structure; [49] and (ii) a co-facial-type packing (referred to as [P:co-facial] Organic photovoltaic (OPV) [1][2][3][4][5][6][7][8] devices have a great potential to become a low-cost technology fo...

We propose a new methodology for the first-principles description of the electronic properties relevant for charge transport in organic molecular crystals. This methodology, which is based on the combination of a nonempirical, optimally tuned range-separated hybrid functional with the polarizable continuum model, is applied to a series of eight representative molecular semiconductor crystals. We show that it provides ionization energies, electron affinities, and transport gaps in very good agreement with experimental values, as well as with the results of many-body perturbation theory within the GW approximation at a fraction of the computational costs. Hence, this approach represents an easily applicable and computationally efficient tool to estimate the gas-to-crystal phase shifts of the frontier-orbital quasiparticle energies in organic electronic materials.

We present a versatile approach for tuning the surface functionality of an atomically precise 25 atom gold cluster using specific host-guest interactions between β-cyclodextrin (CD) and the ligand anchored on the cluster. The supramolecular interaction between the Au25 cluster protected by 4-(t-butyl)benzyl mercaptan, labeled Au25SBB18, and CD yielding Au25SBB18∩CDn (n = 1, 2, 3, and 4) has been probed experimentally using various spectroscopic techniques and was further analyzed by density functional theory calculations and molecular modeling. The viability of our method in modifying the properties of differently functionalized Au25 clusters is demonstrated. Besides modifying their optoelectronic properties, the CD moieties present on the cluster surface provide enhanced stability and optical responses which are crucial in view of the potential applications of these systems. Here, the CD molecules act as an umbrella which protects the fragile cluster core from the direct interaction with many destabilizing agents such as metal ions, ligands, and so on. Apart from the inherent biocompatibility of the CD-protected Au clusters, additional capabilities acquired by the supramolecular functionalization make such modified clusters preferred materials for applications, including those in biology.

Donor-acceptor organic solar cells often show high quantum yields for charge collection, but relatively low open-circuit voltages (V) limit power conversion efficiencies to around 12%. We report here the behavior of a system, PIPCP:PCBM, that exhibits very low electronic disorder (Urbach energy less than 27 meV), very high carrier mobilities in the blend (field-effect mobility for holes >10 cm V s), and a very low driving energy for initial charge separation (50 meV). These characteristics should give excellent performance, and indeed, the V is high relative to the donor energy gap. However, we find the overall performance is limited by recombination, with formation of lower-lying triplet excitons on the donor accounting for 90% of the recombination. We find this is a bimolecular process that happens on time scales as short as 100 ps. Thus, although the absence of disorder and the associated high carrier mobility speeds up charge diffusion and extraction at the electrodes, which we measure as early as 1 ns, this also speeds up the recombination channel, giving overall a modest quantum yield of around 60%. We discuss strategies to remove the triplet exciton recombination channel.

The gas-phase geometries, binding energies (BEs), vibrational spectra, and electron density topological features of methanol (M), water (W), and methanol-water mixed clusters (M(m)W(n), where m = 0-4 and n = 0-4; m + n < or = 4) have been calculated using Hartree-Fock, second-order Møller-Plesset perturbation, and density functional theory with Becke three-parameter hybrid functional combined with Lee-Yang-Parr correlation functional methods. Bader's "atoms in molecules" theory has been used to analyze the hydrogen bonding network. To understand the effect of cooperativity, we have performed natural bond orbital analysis and reduced variational space decomposition analysis. The results show that BEs of methanol and mixed clusters are higher than those of water clusters due to the electron-donating nature of the methyl group. These findings are in accordance with the role of cooperative polarization and cooperative charge transfer in the methanol and mixed clusters. As the size of the cluster increases, the contribution from the cooperative effects also increases. The cooperativity contributes approximately 14 and 24% of stabilization in trimers and tetramers, respectively. The calculated nu(OH) frequencies at MP2/6-311++G(d,p) are in close agreement with the corresponding experimental values.

Taking the π-conjugated polymers PBDT[2X]T (X = H, F) as model systems, the effects of fluorine substitution on main-chain conformations, packing, and electronic couplings are examined. This combination of molecular dynamics simulations and solid-state NMR shows that a higher propensity for backbone planarity in PBDT[2F]T leads to more pronounced, yet staggered, chain stacking, which generally leads to higher electronic couplings and binding energy between neighboring chains.