Doping–Dedoping Interplay to Realize Patterned/Stacked All-Polymer Optoelectronic Devices

Abstract

One of the remaining keys to the success of polymer electronics is the ability to systematically pattern/stack polymer semiconductors with high precision. This paper reports the precise patterning and stacking of various polymer semiconductors with the assistance of a molecular oxidizing agent and reducing agent for donor and acceptor semiconductors, respectively. Such doping-induced solubility control methods have been previously well developed; however, practical applications to various optoelectronic devices have been limited. To pattern/stack various polymers in various dimensions, it is important to carefully design not only the doping method for desolubilizing polymer semiconductors but also the dedoping method for recovering the genuine characteristics of each polymer semiconductor. Based on a systematic approach for such a doping–dedoping interplay, various high-performance optoelectronic devices are demonstrated: (1) all-polymer complementary inverter pattern with a high gain of 176, (2) all-polymer planar heterojunction photodiode with green-selective nature and high specific detectivity over 1012 Jones, and (3) all-polymer ambipolar transistor pattern with balanced hole and electron mobilities. The results of the study indicate the potential of practical application of the doping–dedoping interplay to lateral/vertical patterning of different polymer semiconductors with high precision.

Super-Resolution Photothermal Patterning in Conductive Polymers Enabled by Thermally Activated Solubility

“…Our group recently pioneered a class of submicron patterning methods for semiconducting polymers, collectively called dopant-induced solubility control (DISC), which allow lateral and vertical patterning of conjugated polymers without chemical modification of the polymer. − DISC patterning uses charge transfer dopants to modify the solubility of the polymer: doped regions become insoluble, while undoped regions remain soluble in normal nonpolar solvents . Therefore, we can pattern the polymer by generating a doping gradient and exposing the film to a good solvent for the undoped polymer.…”

Enhancing Doping Efficiency of Diketopyrrolopyrrole-Copolymers by Introducing Sparse Intramolecular Alkyl Chain Spacing

“…The voltage gain was obtained from d V out /d V in of the voltage transfer at V M , where the highest value was 162 at a V DD of 40 V (Figure c). This gain value is among the highest ever reported for all-polymer complementary inverters, thus highlighting the doping compatibility of P1. ,− …”

“…When the polymer is doped in the solution state, the solubility is reduced owing to the formation of ionized polymer units. The morphology of the resulting thin film varies, depending on the doping efficiency, thereby making it very difficult to conduct comparative studies. , Therefore, in this study, we introduce sublimation doping onto the already fabricated polymer thin films to maintain uniform morphologies. ,, Additionally, since sublimation doping can be combined with shadow mask techniques, DISC patterning can also be utilized. , To track the doping/dedoping aspect of each polymer (P1, P2, and DPP-DTT), the UV-Vis absorption spectra for each polymer at each stage of doping/dedoping were recorded and are summarized in Figure . For both P1 and P2, after doping, the genuine absorption feature of the pristine polymer is bleached and, at the same time, the polaronic absorption (1000–1700 nm) of the terpolymer is increased. , However, the polaronic absorption of DPP-DTT showed a negligible increase, and bleaching of the main absorption region was rarely observed.…”

“…To fabricate an all-polymer complementary inverter, an n-type copolymer, poly­[ N , N -bis­(2-octyldodecyl)-naphthalene-1,4,5,8-bis­(dicarboximide)-2,6-diyl- alt -5,5-(2,2-bithiophene)] (PNDI-2T), was introduced. The n-type organic semiconductors are doped with a mechanism in which electrons move from the dopant to the polymer in the opposite direction to the p-type. , Here, we need to address that we introduced n-type PNDI-2T instead of the n-type mode of ambipolar P1 or P2 due to the non-ideal threshold voltages of P1 and P2 transistors. , According to previous studies, PNDI-2T can be efficiently doped with 1,8-diazabicyclo[5.4.0]­undec-7-ene (DBU) and can recover its original crystallinity and electron mobility after patterning using the DISC method. , An optical image of the patterned complementary inverter is shown in Figure a. The voltage transfer characteristics (VTC) at various supply voltages ( V DD = 10, 20, 30, and 40 V) are shown in Figure b.…”

“…Although the intrinsic semiconducting properties of DPP-copolymers are superior, an important drawback of DPP-based D-A copolymers is their low efficiency of molecular doping. − For use in modern optoelectronic devices, polymeric semiconductors should be molecularly doped to reduce ohmic losses in hole/electron transport layers and lower injection barriers at the electrode interface. , One example is a p-i-n multilayer device, where p-doped holes and n-doped electron transport layers sandwich intrinsically active layers, as can be seen from the emission layers in organic light-emitting diodes (OLEDs) or photovoltaic layers in organic and perovskite solar cells. − Thermoelectric devices are another example with a lack of molecular doping, where enhancing electrical conductivity is the most important task to yield a high power factor. − Furthermore, the doping-induced solubility control (DISC) method, which is one of the easiest patterning methods for polymer semiconductors, cannot be considered. − This raises the issue of why DPP-based D-A copolymers exhibit low doping efficiency. In fact, most D-A copolymers have shown relatively low doping efficiencies.…”