Controlling Interface Morphology and Layer Crystallinity in Organic Heterostructures: Microscopic View on C₆₀ Island Formation on Pentacene Buffer Layers

Abstract

Controlling the crystallinity of organic thin films is an important aspect in the improvement of organic electronic devices. However, because of high molecular mass, structural anisotropy, and weak intermolecular van der Waals bonding, crystalline ordering is not easily accomplished. While film preparation at elevated substrate temperature often improves the crystalline quality, this approach cannot be applied to temperature-sensitive materials such as plastic foils used as substrates for flexible electronics. Here, we examine in detail a low-temperature approach to improve film crystallinity by using ultrathin pentacene (PEN) buffer layers that allow crystalline growth of buckminsterfullerene (C 60 ) thin films while without such buffer layers, only amorphous fullerene films are formed upon room-temperature deposition on various support substrates. Remarkably, this effect depends critically on the thickness of the PEN buffer and requires a thickness of at least two monolayers to induce crystalline growth, whereas a buffer layer consisting of a monolayer of PEN again yields amorphous C 60 films. Combining crystallographic investigations by X-ray diffraction and atomic force microscopy measurements, we determine distinct nucleation sites on buffer layers of different thickness, which are correlated to the amorphous, respectively crystalline C 60 islands. Our microscopic analysis reveals distinct differences for the nucleation and diffusivity of fullerenes on the PEN monolayer and on thicker buffer layers, which are attributed to the molecular arrangement in the PEN monolayer. Finally, we show that the crystalline C 60 films are exclusively (111)-oriented and the fullerene islands are even heteroepitaxially aligned on the PEN buffer.

Impact of Nanomorphology on Surface Doping of Organic Semiconductors: The Pentacene–C60F48 Interface

“…In line with our results, we note that for the buckminsterfullerene (C60), a PEN thickness of at least two monolayers is required to induce crystalline growth. 27 In the case of the PEN monolayer, one should not neglect the effect of charge transfer with the substrate that can contribute to diminish the C60F48−C60F48 cohesion due to repulsion between charged molecules.…”

“…expected low diffusion and intermixing with the OSC). 25 While the importance of the acceptor/donor interface morphology has long been recognized and investigated for C60/pentacene as prototype case study, [26][27][28][29][30] the system C60F48/pentacene remains unexplored. Here, the role of the epitaxial quality and morphological characteristics of the OSC layer on the nucleation and growth mode of the dopant as well as the effects on the electronic properties of the interface are investigated.…”

Morphological, structural and electrical properties of pentacene thin films grown via thermal evaporation technique

“…Nevertheless, both thin-film and bulk phases are crystalline and firmly structured. The crystalline size, D, for each peak of pentacene with different deposition times included in Table 1 by using Debye-Scherrer formula [21],…”

Effect of masses of active layers of C60-4-methylphenylhydrazone N-isoamylisatin fullerene heterostructures on their rectifying characteristics

“…devices with the use of organic materials. Organic electronics is gaining popularity due to the low cost of manufacture, the reduction in the weight of materials [2] and the feasibility of producing devices with a larger surface area using flexible substrates [3]. Recent developments in the field of photovoltaics have made it possible to obtain organic solar cells with an efficiency of > 11% [4,5].…”