Baking soda: an ultra-cheap and air stable electron injection layer for organic electronic devices

Abstract

To realize high performance printed organic optoelectronic devices, the development of air-stable, cheap, and solution-processable electron injection layers (EILs) is urgently required to avoid the use of a low work-function metal electrode with poor air stability. We report sodium bicarbonate (baking soda, NaHCO₃) as an efficient, low-cost, air-stable, and environmentally friendly EIL material in various printed organic electronic devices including organic solar cells (OSCs), organic light-emitting diodes (OLEDs), organic photodiodes (OPDs) and n-channel organic thin film transistors (OFETs). UV photoelectron spectroscopy results indicated that the work-function of various common electrodes used for organic devices such as ITO, Au, Al and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) decreased significantly by more than 1 eV following deposition of a thin NaHCO₃ film. The performance and stability of these organic devices improved by around 15% overall with ultra-cheap, air stable EILs. In particular, high performance OSCs based on PTB7:PC₇₁BM with a power conversion efficiency of 8.40% and solution processed OLEDs based on PVK:PBD:Ir(ppy)₃ with light emitting efficiencies of 68.5 cd A⁻¹ and 20 lm A⁻¹ were achieved by applying a NaHCO₃ interlayer.