From Chiral Islands to Smectic Layers: A Computational Journey Across Sexithiophene Morphologies on C₆₀

Abstract

1wileyonlinelibrary.com in favorable cases by atomistic molecular dynamics (MD) simulations. [ 9,[13][14][15][16] Further development in improving the performance of OSC requires a deeper knowledge and ability to control the molecular organization at the interface between the materials playing the role of electron donor and acceptor. Important factors are the choice of donors and acceptors chemical nature, their morphology and the type of heterojunction, which currently consists of either a planar interface between two thin layers of donor and acceptor (bilayer cell, [ 17 ] possibly replicated) tandem cells, [ 18,19 ] or an interpenetrated bicontinuous arrangement where the D, A materials are microsegregated inside a single photoactive layer (bulk heterojunction or BHJ). [ 20,21 ] The orientation of donor and acceptor molecules at their interface and in particular the possibility of, say, "face-face" instead of "edge on" disposition of the respective aromatic moieties is of great importance for bilayer, as well as for BHJ cell performances. [ 22,23 ] As far as materials are concerned, both small molecules and polymers have and are being used. In general terms of efficiency polymer based devices, more extensively studied, have shown the best top performance, but small molecule cells are now showing similar results. [ 24,25 ] Small molecules have the advantage of being of a well-defi ned chemical composition: they can be easily purifi ed and their physical properties can be determined and controlled favoring a better reproducibility of solar cell performance with respect to the batch to batch variations often found in polymers. While chemical composition represents an essential aspect, polymorphism for crystalline materials or more generally the detailed molecular arrangement in space (e.g., the type of mesophase for liquid crystalline materials) [ 26 ] plays an important role. For small molecule materials these aspects can be thermodynamically controlled and well defi ned reaching equilibrium conditions at a certain temperature T , pressure P , and composition. However molecular organizations can very signifi cantly change in thin nanometric fi lms and, moreover, the fi lm preparation process can be a nonequilibrium one making the fi nal result even more diffi cult to predict.Here we wish to investigate the possibility of controlling morphology at a donor-acceptor interface prepared with a physical vapor deposition process, applying a methodology we have recently developed and applied to the deposition of pentacene From Chiral Islands to Smectic Layers: A Computational Journey Across Sexithiophene Morphologies on C 60Gabriele D'Avino , Luca Muccioli , and Claudio Zannoni* A theoretical investigation of the molecular organization at a sexithiophene (T6)-C 60 fullerene planar heterojunction, based on atomistic molecular dynamics, is presented, in which the effect of two different sample preparation processes on the resulting interface morphology is explored. First, the landing of T6 on C 60 (001) substrate is consid...

Shape segregation in molecular organisation: a combined X-ray scattering and molecular dynamics study of smectic liquid crystals

“…100 molecules, [45][46][47][48] providing only limited information on the smectic phase structure. The more recent ability to simulate larger systems of up to a few thousand molecules has prompted investigations into a wide range of systems exhibiting smectic phases, such as semi-fluorinated alkanes, 49,50 azobenzenecontaining moieties, 51 and large aromatic species such as sexithiophene 52,53 and quinquephenyl. 54 A significant focus of MD studies has also been on force field parameterisation and verification, most commonly for the ubiquitous cyanobiphenyl-based liquid crystals, enabling experimental transition temperatures, orientational order parameters, and translational order parameters of the smectic phases to be replicated.…”

Computational Design of Thermally Activated Delayed Fluorescence Materials: The Challenges Ahead

“…Besides, simulations predict the orientation distribution of the emitters and, more generally, provide the molecular positions of carriers and emitters, which are fundamental ingredients for device modeling, and in particular for kinetic simulations of electronic processes. 74 Note that emitting layers are typically (meta)stable, disordered or partially ordered glasses, and host and emitter molecules themselves (Figure 1 scheme pioneered by some of us for the vapor deposition of organic crystalline semiconductors, 76,77 have gained increasing popularity in the OLED research field. [78][79][80][81] The origin of this trend is two-fold: on the one hand, real TADF-based active layers are in fact prepared most often by co-deposition of (at least) one host semiconductor and a guest TADF emitter, 82 and on the other hand, since these films are amorphous, it is difficult to validate the simulation results versus experimental structural data, and it is tempting to believe that mimicking the experimental process could improve the quality of the predictions.…”

Deposition Growth and Morphologies of C60 on DTDCTB Surfaces: An Atomistic Insight into the Integrated Impact of Surface Stability, Landscape, and Molecular Orientation

“…In this contribution, we have mimicked vapor‐phase deposition and growth of C 60 on different DTDCTB substrate surfaces via nonequilibrium atomistic molecular dynamics (MD) simulations . Using this scheme, Muccioli and co‐workers have investigated the crystal growth of pentacene or sexithiophene on the C 60 (001) substrate, while the relationship between different surface properties and thin‐film morphologies is yet to be revealed .…”