The lowest energy Frenkel and charge-transfer excitons in quasi-one-dimensional structures: application to MePTCDI and PTCDA crystals

Hoffmann, Michael J.; Schmidt, Karin; Fritz, Torsten; Hasche, T.; Agranovich, V.M.; Leo, Karl

doi:10.1016/s0301-0104(00)00157-9

Cited by 234 publications

(297 citation statements)

References 43 publications

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“…where ܴሺ‫,ܧ‬ ݀ሻ denotes in our case the reflectivity of the sample stack consisting of the quartz 1 MLE of PTCDA partially potassium-doped providing pronounced new features of PTCDA radical anions at low photon energies (investigated in detail previously 32 ), polycrystalline (pc) PTCDA 33 and the dramatically broadened spectra of 1 MLE of PTCDA on Au(111) and Ag(111) 34,35 are shown in the bottom panel. b) Δ‫ܴܵܦ‬ of PTCDA on quartz glass for nominal thicknesses ranging from submonolayers up to 1 MLE.…”

Section: Resultsmentioning

confidence: 99%

Integer Charge Transfer and Hybridization at an Organic Semiconductor/Conductive Oxide Interface

et al. 2015

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We investigate the prototypical hybrid interface formed between PTCDA and conductive ndoped ZnO films by means of complementary optical and electronic spectroscopic techniques.We demonstrate that shallow donors in the vicinity of the ZnO surface cause an integer charge transfer to PTCDA, which is clearly restricted to the first monolayer. By means of DFT calculations, we show that the experimental signatures of the anionic PTCDA species can be understood in terms of strong hybridization with localized states (the shallow donors) in the substrate and charge back-donation, resulting in an effectively integer charge transfer across the interface. Charge transfer is thus not merely a question of locating the Fermi level above the PTCDA electron-transport level, but requires rather an atomistic understanding of the interfacial interactions. The study reveals that defect sites and dopants can have a significant influence on the specifics of interfacial coupling and thus on carrier injection or extraction.

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Section: Resultsmentioning

confidence: 99%

Integer Charge Transfer and Hybridization at an Organic Semiconductor/Conductive Oxide Interface

et al. 2015

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“…12, 13,20,25,33 When |J k=0 − U| ≫ |t e + t h | (Figure 3a), the diabatic FE and CTE bands are energetically well separated, limiting the FE/ CTE mixing. In this regime, FE/CTE mixing is dominated by the first-order processes described by eq 12; only CT states characterized by p = π/N, 3π/N, ... appreciably mix with the FE, as very little second-order mixing between CT states occurs via indirect coupling through the FE state.…”

Section: Journal Of the American Chemical Societymentioning

confidence: 99%

“…Coupling between the CT states and the optically allowed FE depends on the sum |t e + t h |, in agreement with previous works. 12, 13,[20][21][22][23][24][25]33 Importantly, this sum also determines the coupling between CT states of different electron/hole radii (see eq 7) and thus the k = 0 CT bandwidth (see Figure 6a−c). 33 Hence, the relative phases of the CT integrals determine not only the probability of the excitation existing in a charge-separated state after absorption but also the extent to which the electron and hole are separated in such states.…”

Section: Journal Of the American Chemical Societymentioning

confidence: 99%

Extended-Charge-Transfer Excitons in Crystalline Supramolecular Photocatalytic Scaffolds

Hestand

Kazantsev²,

Weingarten³

et al. 2016

J. Am. Chem. Soc.

105

158

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Coupling among chromophores in molecular assemblies is responsible for phenomena such as resonant energy transfer and intermolecular charge transfer. These processes are central to the fields of organic photovoltaics and photocatalysis, where it is necessary to funnel energy or charge to specific regions within the system. As such, a fundamental understanding of these transport processes is essential for developing new materials for photovoltaic and photocatalytic applications. Recently, photocatalytic systems based on photosensitizing perylene monomimide (PMI) chromophore amphiphiles were found to show variation in hydrogen gas (H 2 ) production as a function of nanostructure crystallinity. The 2D crystalline systems form in aqueous electrolyte solution, which provides a high dielectric environment where the Coulomb potential between charges is mitigated. This results in relatively weakly bound excitons that are ideal for reducing protons. In order to understand how variations in crystalline structure affect H 2 generation, two representative PMI systems are investigated theoretically using a modified Holstein Hamiltonian. The Hamiltonian includes both molecular Frenkel excitations (FE) and charge-transfer excitations (CTE) coupled nonadiabatically to local intramolecular vibrations. Signatures of FE/CTE mixing and the extent of electron/hole separation are identified in the optical absorption spectrum and are found to correlate strongly to the observed H 2 production rates. The absorption spectral signatures are found to sensitively depend on the relative phase between the electron and hole transfer integrals, as well as the diabatic energy difference between the Frenkel and CT exciton bands. Our analysis provides design rules for artificial photosynthetic systems based on organic chromophore arrays.

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“…The E FR is much lower than the E CT in the spin triplet channel (υ = 0), because Ẅ >> Ŵ, therefore the lowest triplet exciton is predominantly FR exciton in molecular crystals. However, whether the lowest singlet exciton is CT or FR depends on the relative strength of υ and Ẅ, e.g., FR for picene 14 but a mixture of CT and FR for pentacene 14,26,27 and PTCDA 26,27,55 . For the PTB7 crystal, the on-site attractive e-h interaction Ẅ may be close to the sum of inter-site attractive matrix elements Ŵ due to the strong inter-chain π-π interaction.…”

Section: Optical Excitationsmentioning

confidence: 99%

Electronic and optical excitations of the PTB7 crystal: First-principles GW-BSE calculations

Kontsevoi

Freeman

2014

Phys. Rev. B

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Given the recent success in achieving efficient organic photovoltaic solar cells based on thieno [3,4-b]thiophene/benzodithiophene polymers (PTB7) and growing efforts to further improve the power conversion efficiency of the PTB7-based devices, a detailed atomic-scale picture of the electronic structure and the excitonic properties of PTB7 crystal is highly desirable.We report electronic and optical properties of PTB7 on the basis of first-principles density functional theory and GW many-body plus Bethe-Salpeter equation (GW-BSE) calculations. It is established that the first two highest valence bands (HVB) and the first two lowest conduction bands (LCB) originate from the benzodithiophene (BDT) and thieno [3,4-b]thiophene (TT) functional units, respectively, thus confirming the donor-acceptor nature of PTB7. A significant difference of band-splitting between HVBs and LVBs is found and its origins are explained. Our results strongly suggest that the strength of the inter-chain π-π interaction is not only a function of inter-chain distance, but is also highly dependent on the nature of the fused rings. The experimental optical absorption spectrum of PTB7 is well reproduced and explained by our 2 GW-BSE calculations. Further analysis shows that the nature of the lowest singlet (triplet) excitons in polymeric crystals such as PTB7 differs from that of organic molecular crystals. A possible reason is explored by combining BSE calculations with a simple Hamiltonian model.

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The lowest energy Frenkel and charge-transfer excitons in quasi-one-dimensional structures: application to MePTCDI and PTCDA crystals

Cited by 234 publications

References 43 publications

Integer Charge Transfer and Hybridization at an Organic Semiconductor/Conductive Oxide Interface

Integer Charge Transfer and Hybridization at an Organic Semiconductor/Conductive Oxide Interface

Extended-Charge-Transfer Excitons in Crystalline Supramolecular Photocatalytic Scaffolds

Electronic and optical excitations of the PTB7 crystal: First-principles GW-BSE calculations

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