Effects of hydrogen bonds between polymeric hole-transporting material and organic cation spacer on morphology of quasi-2D perovskite grains and their performance in light-emitting diodes.

Perovskite is emerging as a novel emitter in solution-processed light-emitting diodes (LEDs). In these LEDs, morphology, especially the grain size of perovskite, plays a key role in determining electroluminescence performance. Several studies have shown that sizes of the perovskite grains can be controlled by the contact angle between the perovskite solution and the substrate. In this work, we found that quasi-2D perovskite grain size can be substantially refined when there are hydrogen bonding between the perovskite's organic spacer and the substrates. In fact, with the presence of such hydrogen bond, its effects on perovskite grain size overshadow the contact angle's effect. We demonstrated that perovskite with refined grains can form on amine- or carbazole-based polymers which can form NH hydrogen bonding with the perovskite's organic spacer. By using these polymers as hole-transporting layers on PEDOT:PSS, external quantum efficiency of CsPbBr3-based LEDs can be enhanced from 1.5% to 10.0% without passivation treatment. This work suggests that bonding between perovskite precursors and the substrate can have significant influences on the morphology of the final perovskite grains and their optoelectronic performance.