Enabling efficient electron injection in stretchable OLED

Stretchable organic light-emitting diodes (OLEDs) are transforming human-machine interfaces and wearable technologies. However, for intrinsically stretchable OLEDs, the performance is still considerably inferior to commercial, non-stretchable OLEDs, with inefficient electron injection being one of the main limiting factors. Herein, we present stretchable designs for both the electron transport layer (ETL) and the cathode in stretchable OLEDs, which achieves an ideal energy-level alignment with the emitting layer for efficient electron injection. For the ETL, we design a copolymer structure combining electron-deficient conjugated groups and alkyl chains, achieving balanced electron transport and stretchability. With ideal electron and exciton energy levels, the stretchable polymer ETL enables OLED performance comparable to that of commonly used small-molecule ETL. For the cathode, we leverage the embrittlement effect of liquid metals to confer stretchability to aluminum thin films, without compromising its electrical and optical characteristics. Combining these designs, we demonstrate fully stretchable OLED devices with a record-high external quantum efficiency (EQE) of 8% and a record-low turn-on voltage of 3.5 V, which are on par with the performance of the utilized emitter measured in rigid OLED devices. This work tackles a crucial bottleneck in stretchable OLED development, bridging the performance gap between fully stretchable OLEDs and standard rigid OLEDs at the device level, and paving the way for high-performance, skin-like displays.