Laminated Graphene Films for Flexible Transparent Thin Film Encapsulation

We introduce a simple, inexpensive, and large-area flexible transparent lamination encapsulation method that uses graphene films with polydimethylsiloxane (PDMS) buffer on polyethylene terephthalate (PET) substrate. The number of stacked graphene layers (<i>n</i>_G) was increased from 2 to 6, and 6-layered graphene-encapsulation showed high impermeability to moisture and air. The graphene-encapsulated polymer light emitting diodes (PLEDs) had stable operating characteristics, and the operational lifetime of encapsulated PLEDs increased as <i>n</i>_G increased. Calcium oxidation test data confirmed the improved impermeability of graphene-encapsulation with increased <i>n</i>_G. As a practical application, we demonstrated large-area flexible organic light emitting diodes (FOLEDs) and transparent FOLEDs that were encapsulated by our polymer/graphene encapsulant

Degradation Protection of Color Dyes Encapsulated by Graphene Barrier Films

The decolorization of paintings, photographs, and artworks is a common phenomenon related to the oxidative degradation of color dyes reacting with oxygen or water molecules, which also causes a critical problem in organic light-emitting diodes (OLEDs). It is expected that the gas-impermeable property of graphene and h-BN can be utilized to protect the color dyes from degradation. However, the transfer method has been limited to a polymer with high glass transition temperature (Tg) or a glass substrate due to hot or wet transfer conditions. Here, we report the dry transfer coating of the graphene barrier films on flexible substrates at room temperature using a roll-to-roll process to prevent the bleaching of color dyes, which can be widely used to protect various colorization and light-emitting materials for sustainable printing and display technologies in the future

Quantifying Doping Efficiency to Probe the Effects of Nanoscale Morphology and Solvent Swelling in Molecular Doping of Conjugated Polymers

We study the doping of conjugated polymers from droplets of molecular dopant solutions, as might be used in additive manufacturing approaches. We compare the doping efficiency of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) solutions between two model conjugated polymers, regioregular poly­(3-hexylthiophene) (P3HT) and poly­(bithiophene-thienothiophene) copolymer with a triethylene glycol side chain (P­(g32T-TT)). We find that F4TCNQ dopes P­(g32T-TT) more efficiently from solution, producing films with >103 times higher conductivity. Using spectroelectrochemistry to calibrate polaron spectra to known hole injection levels, we quantify the doping efficiency (polarons created/dopant molecule added) to be higher than 170% for P­(g32T-TT) but only 47.2% for P3HT. We further explore the differences in molecular doping using a combination of scanning Kelvin probe microscopy (SKPM) and conductive atomic force microscopy (cAFM). We explore doping efficiency and aggregation as a function of the solvent of the dopant solution, side chain, and regioregularity of conjugated polymers; we show that the doping efficiency and dopant aggregation are both correlated with the ability of the dopant/solvent solution to swell the conjugated polymer, with combinations that swell, resulting in more efficient doping and smoother films with less aggregation

Solution-Processed n‑Type Graphene Doping for Cathode in Inverted Polymer Light-Emitting Diodes

n-Type doping with (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)­phenyl) dimethylamine (N-DMBI) reduces a work function (WF) of graphene by ∼0.45 eV without significant reduction of optical transmittance. Solution process of N-DMBI on graphene provides effective n-type doping effect and air-stability at the same time. Although neutral N-DMBI act as an electron receptor leaving the graphene p-doped, radical N-DMBI acts as an electron donator leaving the graphene n-doped, which is demonstrated by density functional theory. We also verify the suitability of N-DMBI-doped n-type graphene for use as a cathode in inverted polymer light-emitting diodes (PLEDs) by using various analytical methods. Inverted PLEDs using a graphene cathode doped with N-DMBI radical showed dramatically improved device efficiency (∼13.8 cd/A) than did inverted PLEDs with pristine graphene (∼2.74 cd/A). N-DMBI-doped graphene can provide a practical way to produce graphene cathodes with low WF in various organic optoelectronics