Role of Dopants in Long-Range Charge Carrier Transport for p-Type and n-Type Graphene Transparent Conducting Thin Films

Abstract

Monolayer to few-layer graphene thin films have several attractive properties such as high transparency, exceptional electronic transport, mechanical durability, and environmental stability, which are required in transparent conducting electrodes (TCs). The successful incorporation of graphene TCs into demanding applications such as thin film photovoltaics requires a detailed understanding of the factors controlling long-range charge transport. In this study, we use spectroscopic and electrical transport measurements to provide a self-consistent understanding of the macroscopic (centimeter, many-grain scale) transport properties of chemically doped p-type and n-type graphene TCs. We demonstrate the first large-area n-type graphene TCs through the use of hydrazine or polyethyleneimine as dopants. The n-type graphene TCs utilizing PEI, either as the sole dopant or as an overcoat, have good stability in air compared to TCs only doped with hydrazine. We demonstrate a shift in Fermi energy of well over 1 V between the n- and p-type graphene TCs and a sheet resistance of ~50 Ω/sq at 89% visible transmittance. The carrier density is increased by 2 orders of magnitude in heavily doped graphene TCs, while the mobility is reduced by a factor of ~7 due to charged impurity scattering. Temperature-dependent measurements demonstrate that the molecular dopants also help to suppress processes associated with carrier localization that may limit the potential of intrinsic graphene TCs. These results suggest that properly doped graphene TCs may be well-suited as anodes or cathodes for a variety of opto-electronic applications.

Facile Doping and Work‐Function Modification of Few‐Layer Graphene Using Molecular Oxidants and Reductants

“…The moderate reduction of the mobility in doped FLG in this work (24% and 17% for the strongest p-and ndopants, respectively) can be contrasted to the larger reductions of mobility in doped SLG (26-80%) as summarized in Table S5. [70][71][72][73][74][75] This difference can be attributed to the fact that charged impurities can be screened by each additional graphene layer, [68] so that Coulomb scattering of the charged dopant ions on the surface of FLG doesn't significantly affect the mobility of the buried layers of FLG. The smaller decrease in mobility for FLG on doping, therefore, less significantly offsets the accompanying increase in carrier density than in SLG.…”

Multifunctional oxides for integrated manufacturing of efficient graphene electrodes for organic electronics

“…9,18,19 The doping is not only environmentally stable but also withstands elevated temperatures beyond 100 C, which is a clear advantage compared to conventional doping approaches, e.g., nitride acids. 17,21,22 In addition, the metal oxides allow for an efficient charge injection from graphene into the OLED due to a favorable energy matching of the transport levels. 9,18,19 However, industrial applications also require integrated process solutions [(3) and (4)].…”

“…[23][24][25][26] Further, lithography typically involves the use of solvents and chemicals that might affect or degrade the properties of doped graphene. [8][9][10][11]21,[27][28][29][30][31] Here, we show that all of these challenges for efficient graphene-based TCEs can be effectively addressed at once via a thin (>10 nm) metal oxide (MoO 3 or WO 3 ) coating of the graphene. The metal oxide can be deposited by various means, 9,18,19 but we focus here on thermal evaporation.…”

Fluorination of Isotopically Labeled Turbostratic and Bernal Stacked Bilayer Graphene

“…[9] Doping of graphene results in a shift of the G-band frequency, indicating that the Fermi energy has been shifted away from the Dirac point. [21] However, the G-peak position also depends on strain. [22] Large maps with several grains and with thousands of pixels are investigated here, so the influence of local strain and other random factors can be discriminated by statistical evaluation.…”