Comparative Study of the N‐Type Doping Efficiency in Solution‐processed Fullerenes and Fullerene Derivatives

Abstract

Molecular doping of organic semiconductors and devices represents an enabling technology for a range of emerging optoelectronic applications. Although p‐type doping has been demonstrated in a number of organic semiconductors, efficient n‐type doping has proven to be particularly challenging. Here, n‐type doping of solution‐processed C60, C70, [60]PCBM, [70]PCBM and indene‐C60 bis‐adduct by 1H‐benzimidazole (N‐DMBI) is reported. The doping efficiency for each system is assessed using field‐effect measurements performed under inert atmosphere at room temperature in combination with optical absorption spectroscopy and atomic force microscopy. The highest doping efficiency is observed for C60 and C70 and electron mobilities up to ≈2 cm2/Vs are obtained. Unlike in substituted fullerenes‐based transistors where the electron mobility is found to be inversely proportional to N‐DMBI concentration, C60 and C70 devices exhibit a characteristic mobility increase by approximately an order of magnitude with increasing dopant concentration up to 1 mol%. Doping also appears to significantly affect the bias stability of the transistors. The work contributes towards understanding of the molecular doping mechanism in fullerene‐based semiconductors and outlines a simple and highly efficient approach that enables significant improvement in device performance through facile chemical doping.

High‐Entropy Mixtures of Pristine Fullerenes for Solution‐Processed Transistors and Solar Cells

“…Evidently, the here investigated fullerene mixtures feature excellent charge transport properties, which are on par with results reported for solution-processed pristine fullerenes. [5,18] It is worth noting that the absence of ordered domains (see Supporting…”

“…Despite their desirable solid-state properties a major disadvantage of pristine C60 and C70 is the seemingly poor solubility in organic solvents, [1,2] which however can be substantially improved by attaching exohedral moieties to the fullerene cage, albeit at the expense of a high electron mobility. [3][4][5] In addition, pristine fullerenes suffer from the strong tendency to crystallize during solvent removal, which complicates formation of continuous thin films. As a result, substituted fullerenes, such as in particular phenyl-Cx-butyric acid methyl esters (PCBMs; x = 61 or 71), are by far the most widely studied electron acceptor material for organic photovoltaic applications.…”

“…Evidently, the here investigated fullerene mixtures feature excellent charge transport properties, which are on par with results reported for solution-processed pristine fullerenes. [5,18] It is worth noting that the absence of ordered domains (see Supporting Information Figure S2), combined with the high symmetry of the fullerene molecules, implies several attractive features such as the absence of grain boundaries, which can impede charge transport, as well as isotropic device characteristics. [19] We further explored the use of pristine fullerene mixtures as an acceptor material for polymer solar cells.…”

Anion-induced N-doping of naphthalenediimide polymer semiconductor in organic thin-film transistors

“…27 Comparative studies of the doping efficiency of fullerene-based OSCs with the same dopant in OTFTs also found a significant enhancement in device performance. 28 However, conjugated polymers, as the major class of solution-processable OSCs, are rarely n-doped in devices, especially OTFTs, 14,20,24,29 despite the significant improvement it can have on device parameters, e.g., charge carrier mobility, threshold voltage, channel current on/off ratio and contact resistance. Amongst the candidate conjugated n-type polymers for OTFTs, naphthalenediimide (NDI) containing copolymers have shown impressive performance to date.…”

Small Molecule/Polymer Blend Organic Transistors with Hole Mobility Exceeding 13 cm2 V−1 s−1

“…To this end, recent work has shown that -under certain circumstances -doping organic semiconductors can indeed yield OTFTs and integrated circuits with improved operating characteristics. [31] [32] To assess the impact of doping, different molecular dopants were investigated with the most promising being the fluorinated fullerene derivative C60F48 [ Figure 2(a)]. [33] [34] [35] The attractive properties associated with C60F48…”