The fabrication of electronic devices based on organic materials, known as 'printed electronics', is an emerging technology due to its unprecedented advantages involving fl exibility, light weight, and portability, which will ultimately lead to future ubiquitous applications. [ 1 ] The solution processability of semiconducting and metallic polymers enables the cost-effective fabrication of optoelectronic devices via high-throughput printing techniques. [ 2 ] These techniques require high-performance fl exible and transparent electrodes (FTEs) fabricated on plastic substrates, but currently, they depend on indium tin oxide (ITO) coated on plastic substrates. However, its intrinsic mechanical brittleness and inferior physical properties arising from lowtemperature ( T ) processing below the melting T of the plastic substrates (i.e., typically below 150 °C) have increased the demand for alternative FTE materials. [ 3 ] Conducting polymers (CPs) have been considered a promising candidate for FTEs due to their mechanical fl exibility and solution processability. The high transparency of CPs originates from the charge carrier density ( n ) of approximately 10 21 cm −3 because both the refl ectance and absorption are confi ned in the IR region below the plasma frequency ( ω P , ω P 2 = 4 π e 2 n / m * where m * is the effective mass of the charge carrier) at approximately hω P ≈ 1 eV. [ 2 ] A complex of poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(4-styrenesulfonate) (PSS), in which PSS acts as both a counter-ion and a soluble template for PEDOT, is a successful CP due to its high electrical conductivity ( σ dc ) and excellent transparency in the visible range. [ 4 ] The conducting fi lms, which were coated from PEDOT:PSS solution in an aqueous dispersion, consist of hydrophobic and conducting PEDOT-rich grains encapsulated by hydrophilic and insulating PSS-rich shells. [ 5 ] These morphological features involve an excess amount of PSS as well as low chain alignment, resulting in a low σ dc of approximately 1 S cm −1 . Over the past decade, pre-and/or post-treatment with various organic solvents, surfactants, salts, and acids have been found to enhance the σ dc of PEDOT:PSS by two to three orders of magnitude. [6][7][8] Recently, the high σ dc (≈3065 S cm −1 ) was achieved using a treatment of dropping a 1.0 M H 2 SO 4 solution onto the PEDOT:PSS fi lms. [ 8 ] Although numerous studies suggested that the σ dc enhancement could be attributed to morphological changes in the PEDOT:PSS complex, such as grain growth, polymer chain expansion, and phase separation, a clear understanding of the mechanism of the σ dc enhancement is still required for both the basic material studies on CPs and developing high-performance FTEs. [6][7][8] Herein, we report the solution-processed crystalline formation in PEDOT:PSS via H 2 SO 4 post-treatment. By rigorously controlling the post-treatment conditions (i.e., the H 2 SO 4 concentration, treatment T , and processing details), we obtained insight into how the H 2 SO 4 solution proce...

We investigated the charge dynamics of the conductivity enhancement from 2 to 1000 S/cm in poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate) as induced by structural changes through the addition of a polar solvent and the following solvent bath treatment. Our results indicate that the addition of a polar solvent selectively enhanced the π-π coupling of the polymer chains, resulting in the reduction of disorder and tremendously increasing the charge carrier mobility, which yielded an insulator-to-metal transition. In contrast, the following solvent bath treatment selectively enhanced the intergrain coupling, which did not affect the disorder or the mobility but increased the charge carrier density. Therefore, we demonstrate that the conduction-character defining disorder in this conducting polymer system is determined by the extent of interchain coupling.

Small-bandgap polymer solar cells (PSCs) with a thick bulk heterojunction film of 340 nm exhibit high power conversion efficiencies of 9.40% resulting from high short-circuit current density (JSC ) of 20.07 mA cm(-2) and fill factor of 0.70. This remarkable efficiency is attributed to maximized light absorption by the thick active layer and minimized recombination by the optimized lateral and vertical morphology through the processing additive.

Despite the excellent work function adjustability of conjugated polyelectrolytes (CPEs), which induce a vacuum level shift via the formation of permanent dipoles at the CPE/metal electrode interface, the exact mechanism of electron injection through the CPE electron transport layer (ETL) remains unclear. In particular, understanding the ionic motion within the CPE ETLs when overcoming the sizable injection barrier is a signifi cant challenge. Because the ionic functionality of CPEs is a key component for such functions, a rigorous analysis using highly controlled ion density (ID) in CPEs is crucial for understanding the underlying mechanism. Here, by introducing a new series of CPEs with various numbers of ionic functionalities, energy level tuning at such an interface can be determined directly by adjusting the ID in the CPEs. More importantly, these series CPEs indicate that two different mechanisms must be invoked according to the CPE thickness. The formation of permanent interfacial dipoles is critical with respect to electron injection through CPE ETL (≤ 10 nm, quantum mechanical tunneling limit), whereas electron injection through thick CPE ETL (20-30 nm) is dominated by the reorientation of the ionic side chains under a given electric fi eld. Metal ActiveE vac M eff e µ ID CPE LUMO HOMO

Controlled device parameters of high-mobility polymer field-effect transistors (FETs) are demonstrated by modest doping and charge compensation. Through fleeting chemical vapor treatments of aligned poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b']dithiophen-2-yl)-alt-[1,2,5]thiadiazolo-[3,4-c]pyridine] (PCDTPT) thin films as the charge transport layer in the FET channel, the FET properties are tailored by controlling doping concentration of the PCDTPT adjacent to metal electrodes.