Soluble fullerene derivatives: The effect of electronic structure on transistor performance and air stability

Abstract

The family of soluble fullerene derivatives comprises a widely studied group of electron transporting molecules for use in organic electronic and optoelectronic devices. For electronic applications, electron transporting (n-channel) materials are required for implementation into organic complementary logic circuit architectures. To date, few soluble candidate materials have been studied that fulfill the stringent requirements of high carrier mobility and air stability. Here we present a study of three soluble fullerenes with varying electron affinity to assess the impact of electronic structure on device performance and air stability. Through theoretical and experimental analysis of the electronic structure, characterization of thin-film structure, and characterization of transistor device properties we find that the air stability of the present series of fullerenes not only depends on the absolute electron affinity of the semiconductor but also on the disorder within the thin-film.

Solid State Physicochemical Properties and Applications of Organic and Metallo- Organic Fullerene Derivatives

“…Although the symmetry of a derivative is generally lower than that of the parent fullerene, many molecules retain the threefold degeneracy of the LUMOderived band of C 60 . The energy of the HOMO and LUMO electronic levels may be estimated by calculation, cyclic voltammetry measurements, or electron spectroscopy; values obtained with different methods usually show good agreement [12,123]. As may be observed, in covalent C 60 derivatives both levels are generally shifted to less negative energies compared to pristine C 60 , and this is true also for derivatives obtained by the less common fullerene oxidation reactions [120].…”

“…Fig. 4 presents a visual comparison of the energy position of the HOMO and LUMO orbitals of several C 60 derivatives [12,120,121,122]. Although the symmetry of a derivative is generally lower than that of the parent fullerene, many molecules retain the threefold degeneracy of the LUMOderived band of C 60 .…”

“…Electron-based spectroscopy techniques (direct and inverse photoemission, electron-tunnelling spectroscopy) can be employed to probe the occupied and unoccupied electronic density of states in fullerene solids [12,58,124,125,126,127,128]. An example is given in Fig.…”

“…[3,4] For this reason, C 60 is normally stored under noillumination conditions, and C 60 films and devices are only achieved and characterized under vacuum or inert atmosphere, often requiring in situ measurements on freshly deposited samples. Fullerene functionalization can prevent photo-oxidation, either by changing the chemical reactivity of charged fullerene moieties by modifying the energy position of the lowest unoccupied molecular orbital (LUMO) with respect to the trap energy of adsorbed atmospheric oxidants (oxygen and water), or by introducing sideadducts that modify the solid-state structure and act as a barrier against oxygen or water diffusion [11,12].…”

Packing and Disorder in Substituted Fullerenes

“…[1][2][3][4][5] The ability to use synthetic methods to tune their solution processability and (opto)electronic properties, 6 coupled with the propensity of these spherical/ellipsoidal molecules to form three-dimensional aggregate networks with extended percolation pathways in the solid state, have made fullerenes the electron-acceptor material of choice for OPV. 7 While substituted fullerenes have been the target of a multitude of theoretical investigations (based on quantum-chemical calculations, all-atom molecular dynamics (MD) simulations, and coarse-grained simulations) and experimental studies, 1,[8][9][10][11][12][13][14][15][16][17][18][19][20][21] there remain fundamental characteristics to be better understood in order to improve the design of new fullerene-based materials.…”