Phase control for quasi-2D blue emitters by spacer cation engineering

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Vol. 8; no. 32; pp. 1152 - 116
• Main Authors: Tam, Ho Won, Leung, Tik Lun, Sun, Wenting, Liu, Fangzhou, Ma, Chao, Sing Wong, Kam, Lon ari, Ivor, Grisanti, Luca, Ov ar, Juraj, Skoko, eljko, Popovi, Jasminka, Djuriši, Aleksandra B
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 28.08.2020
• Subjects: Carbon; Cations; Chains; Emitters; Morphology; Perovskites; Phase control; Phase distribution; Pinholes; Stoichiometry
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d0tc01631d

The effect of alkylammonium tail length in phenyl-alkyl spacer cations in quasi-2D Ruddlesden-Popper perovskites on the phase distribution in low n films ( n = 2 stoichiometry) is investigated. An increase in alkyl chain length suppresses the formation of the n = 1 phase (and consequently higher n phases), which is attributed to the change in the packing arrangement of spacer cations from parallel (one and two carbon atom alkyl chains) to non-parallel (3 carbon atom alkyl chains). A single blue emission peak corresponding to the n = 3 phase (466 nm) and n = 2 phase (436 nm) is obtained in the PL spectra of phenylpropylammonium quasi-2D perovskites with methylammonium (MA) and formamidinium (FA) cations, respectively. The same trends in phase distribution, namely a reduction in the proportion of the n = 1 phase with increasing alkyl chain length, are observed for both MA- and FA-based perovskites. However, FA-based samples exhibited higher crystallinity but worsened morphology (more pinholes) and less efficient funneling compared to MA-based samples. Consequently, efficient sky-blue LEDs with the highest EQE of 3.35% are obtained for PPA 2 MAPb 2 Br 7 perovskite. Efficient energy funneling in the quasi-2D perovskite exhibiting sky-blue emission is achieved by phase control utilizing a phenyl-alkyl spacer cation.