Effects of Molecular Orientation in Acceptor–Donor Interfaces between Pentacene and C₆₀ and Diels–Alder Adduct Formation at the Molecular Interface

Abstract

Interfaces between pentacene and Buckminster‐fullerene (C60) have attracted interest due to their application as oligomeric model system for organic solar cells. As the actual device characteristics in such implementations are crucially controlled by the interface structure, detailed investigations of this interface on a molecular level are mandatory. In this study, the influence of the orientation of the pentacene molecules in highly ordered crystalline bottom layers on the characteristics of such internal interfaces is analyzed. It has been shown that the interface structure is driven by temperature‐controlled diffusion of C60 molecules to the pentacene step edges in the case of uprightly oriented pentacene. For lying pentacene in the bottom layer, no step‐edge decoration is observed while the wetting of the pentacene layer is enhanced. Furthermore, the stability of the interface against intercalation and reorientation has been analyzed by means of NEXAFS spectroscopy, showing that the orientation of the pentacene molecules at the interface remains unchanged. Instead, strong indication for chemical modification of the molecular entities by the formation of Diels–Alder adducts between C60 and pentacene is observed. Finally, it is shown that C60 forms crystalline islands in thicker films only on top of uprightly oriented pentacene while rather amorphous films are formed on lying pentacene.

Atom Probe Tomography of Molecular Organic Materials: Sub-Dalton Nanometer-Scale Quantification

“…59 We also note that Breuer et al concurrently observed the presence of a reaction at the interface. 60 Because the DAc has a lowest unoccupied molecular orbital (LUMO) energy ∼0.16 eV shallower than C 60 , the presence of the DAc at the interface should affect device properties by preventing electrons from reaching the interface. 61 To test the effects of the DAc on device parameters, we purposefully introduced an "interlayer" of DAc by co-depositing a Tc:C 60 blend at the interface and performed an annealing series to vary the extent of the interfacial reaction.…”

Temperature Dependent Epitaxial Growth of C60 Overlayers on Single Crystal Pentacene

“…[15][16][17] In the present work, the evolution of the crystallinity of a well-ordered bimolecular heterojunction, C 60 on a single crystal surface of pentacene (C 22 H 14 ), is studied depending on the growth temperature by means of surface X-ray diffraction techniques and noncontact mode atomic force microscopy (nc-AFM). [18] The pentacene/C 60 interface has been studied widely, both experimentally [19][20][21][22][23][24] and theoretically. [18] The pentacene/C 60 interface has been studied widely, both experimentally [19][20][21][22][23][24] and theoretically.…”

“…Pentacene (Figure 1a) and C 60 (Figure 1b) are representative p-type (donor) and n-type (acceptor) semiconducting compounds generating an exciton-dissociating interface in a prototypical organic solar cell device. [18] The pentacene/C 60 interface has been studied widely, both experimentally [19][20][21][22][23][24] and theoretically. [25][26][27][28][29][30] It was recently discovered that C 60 crystallizes in its bulk structure epitaxially by aligning the nearest-neighbor face-centered-cubic (fcc)-110 < > axis uniquely along the [110] direction of the pentacene single crystal (Pn-SC) surface.…”

Hexachlorinated Boron(III) Subphthalocyanine as Acceptor for Organic Photovoltaics: A Brief Overview

“…Note that theoretical findings are usually done under the assumption of an inert, molecularly sharp, regular, and pure PHJ (which almost never occurs in the experiments) and lack systematic verification in a representative series of the prototypical devices. For instance, the experimental evidence on the formation of a Diels-Adler adduct at the pentacene/C 60 interface was recently found [62], thus casting doubt on the above results.…”