Spin-Based Diagnostic of Nanostructure in Copper Phthalocyanine–C₆₀ Solar Cell Blends

Abstract

Nanostructure and molecular orientation play a crucial role in determining the functionality of organic thin films. In practical devices, such as organic solar cells consisting of donor-acceptor mixtures, crystallinity is poor and these qualities cannot be readily determined by conventional diffraction techniques, while common microscopy only reveals surface morphology. Using a simple nondestructive technique, namely, continuous-wave electron paramagnetic resonance spectroscopy, which exploits the well-understood angular dependence of the g-factor and hyperfine tensors, we show that in the solar cell blend of C(60) and copper phthalocyanine (CuPc)-for which X-ray diffraction gives no information-the CuPc, and by implication the C(60), molecules form nanoclusters, with the planes of the CuPc molecules oriented perpendicular to the film surface. This information demonstrates that the current nanostructure in CuPc:C(60) solar cells is far from optimal and suggests that their efficiency could be considerably increased by alternative film growth algorithms.

Controlling Ferromagnetic Ground States and Solitons in Thin Films and Nanowires Built from Iron Phthalocyanine Chains

“…We note that the existing indexed structures for FePc correspond to a high temperature preparation traditionally associated with the β‐phase, and that using the structure of α‐CuPc to interpret the diffraction features of FePc films deposited at room temperature is an approach that has been commonly used by other groups . The TEM pattern is as expected from previous studies of the effect of PTCDA on metal phthalocyanine films, although it has been observed that the templated phase can also display (001) planes in TEM due to the spread in the orientation of the molecular crystals …”

“…To characterize the highly anisotropic FePc magnetism, we prepare FePc films with different orientations with respect to the substrate, using the templating technique that was previously applied to other planar phthalocyanines . The unique orientation of the molecules with respect to the magnetic field enables us to model the magnetic properties using the Heisenberg model with planar anisotropy and to extract both the magnetic coupling strength J and the anisotropy constant D .…”

High-temperature antiferromagnetism in molecular semiconductor thin films and nanostructures

“…The magnetic centre is embedded in an organic framework, preventing any phase segregation of magnetic dopants, and offering significant advantages for fabrication compared to inorganics; further spin dilution can be easily achieved by coevaporation28. The rationalization of the unusually large magnetic coupling in terms of a simple model derived from ab initio calculations has established the important role of the out-of-plane orbital, which is unique to CoPc within the transition metal Pc series, but can be used as a guide to design other macrocyclic complexes with strong interactions.…”

Noncovalent interactions of free-base phthalocyanine with elongated fullerenes as carbon nanotube models

“…However, even in this case, the information afforded is often unable to provide a necessary insight into the mechanism of interaction of organic functionalizing species with a carbon nanomaterial. This fact makes one appeal to theoretical tools, in particular to DFT calculations, to fill the above gap, as exemplified in a number of works on Pc hybrids with fullerenes [2][3][4][5][6][7][8][9][10] and graphene [11][12][13][14][15][16][17]. As regards related CNT-based systems, the reports in which theoretical modeling are explored to assist experimental characterization turn to be very scarce [19,20,22].…”

“…In all three instances, we are aware of, DFT calculations using a general gradient approximation (GGA) functional and pseudopotentials were run on periodic single-walled CNT (SWNT) models with covalently [19] and noncovalently [20,22] attached Pc molecules. More specifically, Orellana [19] studied catalytic activity of MPcs (M = Mn, Fe, and Co) covalently bonded to a metallic (8,8) armchair SWNT toward the oxygen reduction reaction. Similarly, Zhu et al [20] addressed theoretically (in addition Electronic supplementary material The online version of this article (doi:10.1007/s11224-017-0955-6) contains supplementary material, which is available to authorized users.…”