memories, and organic field-effect transistors (OFETs), have various advantages including mechanical flexibility, low cost, solution-processed fabrication, and tunable material functionalities by molecular design compared with silicon-based materials. [1][2][3][4][5][6][7][8][9][10][11][12][13] However, the contact resistance problem arising between organic materials and metal electrodes has been one of the dominant obstacles for adopting organic semiconducting devices instead of silicon-based devices. Diverse attempts, for instance, self-assembled monolayer (SAM) treatment on metal electrodes, [14][15][16][17][18][19] inserting a charge injection layer between OSC and metals, [20][21][22][23][24][25][26][27] choice of metals for better injection properties, [28,29] adopting carbon-based conductor like graphene as electrodes, [30] have been introduced to improve carrier injection across typically a non-ohmic contact. Especially, considering large operation voltages required for OFETs, improving contact properties of organic/metal interface is an essential step for practical applications of OSCs.Contact doping is one of the most effective techniques to reduce contact resistance and has been widely employed in silicon-based devices and recently in OSCs to reduce the contact resistance. [31][32][33][34][35][36] In order to avoid undesirable OFF currents, it needs to be performed selectively, i.e., in localized regions at the source-drain contacts only and not in the channel region. The doped regions have been usually confined to the top surface of the OSC film by depositing a small amount of dopants on the top of the organic film by thermal evaporation. As a result, the position of the gate dielectrics was normally restricted to the top side of devices (i.e., FETs in a top-gate structure) in order to enhance the charge injection from metal electrodes to the accumulation layer formed on the top surface of the polymer. [31,32] Recently, the combination of poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F 4 -TCNQ) as host and dopant material, respectively, has produced a highly conducting polymer that has been studied as a candidate for a synthetic metal and high power-factor thermoelectric material. [37][38][39][40][41] Interestingly, this combination achieved an efficient bulk-doping of PBTTT by solid-state diffusion which implied that the F 4 -TCNQ Organic semiconductors (OSCs) have been widely studied due to their merits such as mechanical flexibility, solution processability, and large-area fabrication. However, OSC devices still have to overcome contact resistance issues for better performances. Because of the Schottky contact at the metal-OSC interfaces, a non-ideal transfer curve feature often appears in the low-drain voltage region. To improve the contact properties of OSCs, there have been several methods reported, including interface treatment by self-assembled monolayers and introducing charge injection layers. Here, a selectiv...