Fullerene derivatives with oligoethylene-glycol side chains: an investigation on the origin of their outstanding transport properties.

Riccardo Alessandri,Giuseppe Portale,Daniel M. Balazs,Remco W. A. Havenith,Maria A. Loi,Li Qiu,Jan C. Hummelen,Jingjin Dong,Selim Sami,Siewert J. Marrink,Fatimeh Jahani

doi:10.1039/d1tc02753k

Riccardo Alessandri, Giuseppe Portale

Open Access

https://doi.org/10.1039/d1tc02753k

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Abstract

For many years, fullerene derivatives have been the main n-type material of organic electronics and optoelectronics. Recently, fullerene derivatives functionalized with ethylene glycol (EG) side chains have been showing important properties such as enhanced dielectric constants, facile doping and enhanced self-assembly capabilities. Here, we have prepared field-effect transistors using a series of these fullerene derivatives equipped with EG side chains of different lengths. Transport data show the beneficial effect of increasing the EG side chain. In order to understand the material properties, full structural determination of these fullerene derivatives has been achieved by coupling the X-ray data with molecular dynamics (MD) simulations. The increase in transport properties is paired with the formation of extended layered structures, efficient molecular packing and an increase in the crystallite alignment. The layer-like structure is composed of conducting layers, containing of closely packed C60 balls approaching the inter-distance of 1 nm, that are separated by well-defined EG layers, where the EG chains are rather splayed with the chain direction almost perpendicular to the layer normal. Such a layered structure appears highly ordered and highly aligned with the C60 planes oriented parallel to the substrate in the thin film configuration. The order inside the thin film increases with the EG chain length, allowing the systems to achieve mobilities as high as 0.053 cm2 V−1 s−1. Our work elucidates the structure of these interesting semiconducting organic molecules and shows that the synergistic use of X-ray structural analysis and MD simulations is a powerful tool to identify the structure of thin organic films for optoelectronic applications.

Highlights

For many years, fullerene derivatives have been the main n-type material of organic electronics and optoelectronics
By comparing C60-fused N-methylpyrrolidine-ortho-C12 phenyl (C60OC12), C60-fused N-methylpyrrolidine-meta-C12 phenyl (C60MC12), C60-fused N-methylpyrrolidine-para-C12 phenyl (C60PC12), and C60-fused N-methylpyrrolidine-C12 (C60C12), C60MC12 was found to have the best performance with an electron mobility as high as 0.09 cm[2] VÀ1 sÀ1, which is more than one order of magnitude higher than the others; a current on/off ratio up to 4 Â 105 was observed
organic field effect transistors (OFETs) have been prepared using four different soluble C60 derivatives equipped with pendant ethylene glycol (EG) chains (C60–EG) of different lengths (n = 2 for PDEG-1, 3 for PTEG-1, 4 for PTeEG-1 and 5 for PPEG-1, where n is the number of EG units; see Fig. 1a)

Summary

Introduction

Fullerene derivatives have been the main n-type material of organic electronics and optoelectronics. Solution, for the fabrication of a new generation of electronic and optoelectronic devices, characterized by mechanical flexibility, lightweight properties and cheap fabrication technology In this community, these carbon allotropes have been praised because of their fascinating structural and physical properties and because, initially, they were one of the few molecular systems that could display substantial n-type transport due to their strong electron affinity. Periodic dipoles aid crystallization, resulting in better structural order and a consequent suppressed electronic disorder in the nanomaterials.[14,21,26] the polarity of the EG side chains allows for good solubility and better miscibility with molecular dopants, which leads to a higher doping efficiency that enables conductivity values as high as 2.3 S cmÀ1 and the successful use of C60–EG derivatives as thermoelectric materials (power factor values up to 23 mW KÀ2 mÀ1).[14] the high electron density of these C60 derivatives has been shown to be instrumental in passivating surface defects in metal halide perovskite solar cells.[27,28].

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