UV-curable polymer-treated polydimethylsiloxane substrate for ultrahigh-efficient flexible organic light-emitting diodes

• The thermal stability of PDMS substrate is improved by using NOA63 modification layer. • The interfacial adhesion between PDMS and PEDOT:PSS is enhanced with NOA63. • The NOA63 modification layer also facilitates the light extraction in flexible OLEDs. • The flexible OLEDs achieve an ultrahigh EQE of 65 %. Flexible organic light-emitting diodes (FOLEDs) have developed rapidly and have been successfully implemented in the technology of foldable smartphones. As one of the most promising flexible substrates, polydimethylsiloxane (PDMS) suffers from the drawbacks of low thermal stability and weak interfacial adhesion with the low-cost solution-processed poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) film electrodes. In this work, a UV-curable polymer, Norland Optical Adhesive 63 (NOA63), is proposed to enhance the thermal stability and interfacial adhesion, as well as facilitating the light extraction of PDMS substrate. The PEDOT:PSS electrode film on the NOA63 modified PDMS substrate performs a uniform and smooth surface morphology with a low roughness of 3.1 nm, a high transmittance of 94.7 % at 550 nm wavelength, a low sheet resistance of 160 Ω/sq, and superior mechanical durability even after 18,000 bending cycles. The outstanding characteristics of the PDMS/NOA63 substrate enables the fabrication of an ultrahigh-efficient FOLED with a maximum current efficiency, power efficiency and external quantum efficiency of 230.6 cd/A, 144.9 lm/W and 65 %, respectively. This study paves the way to realize high-performance FOLEDs for wearable electronics in the future.