Gaining Insight into the Underlayer Treatment for in Situ Fabrication of Efficient Perovskite Nanocrystal-Based Light-Emitting Diodes

The feasibility of in situ fabrication of metal halide perovskite films for optoelectronic devices has attracted increasing research interest as it eliminates the material preparation step and thus simplifies the integration procedure. The success of in situ fabrication requires delicate regulations of the underlayers. Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is a universal hole transporting material for solution-processed optoelectronic devices; however, it is usually hard to cast high-quality active layers directly onto the pristine PEDOT:PSS layer due to its unfavored surface properties. The physical changes in the film morphology and optical and electric properties and the chemical change in the molecular composition of the oxygen plasma-treated PEDOT:PSS surface are investigated in this work. It is found that the reduced film thickness and PSS-rich surface after plasma treatment facilitate the growth of upper layers of formamidinium lead bromide (FAPbBr₃) nanocrystal films, leading to higher photoluminescence quantum yields. The magnificent performance of perovskite-based light-emitting diodes (Pe-LEDs) with oxygen plasma-treated PEDOT:PSS shows a highest current efficiency of 54.0 cd/A, which is more than 4 times than those of the analogous Pe-LEDs fabricated with pristine PEDOT:PSS.