Enhanced Light Emission Performance of Mixed Cation Perovskite Films—The Effect of Solution Stoichiometry on Crystallization

Fangzhou Liu, Xinshun Qin, Bing Han*, Christopher C.S. Chan, Chao Ma, Tik Lun Leung, Wei Chen, Yanling He, Ivor Lončarić, Luca Grisanti, Juraj Ovčar, Željko Skoko, Yingli Shi, Francis Chi Chung Ling, Md Rashedul Huqe, Juan Antonio Zapien, Shixun Wang, Chun Jen Su, U. Ser Jeng, Kam Sing WongAlan Man Ching Ng, Meng Gu, Jasminka Popović*, Aleksandra B. Djurišić*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


The performance of quasi-2D perovskite light emitting diodes (LEDs) with mixed small cations, cesium and formamidinium (FA), is significantly affected by their ratio. The best devices obtained for Cs:FA ratio of 1:1 exhibit a maximum external quantum efficiency (EQE) of 12.1%, maximum luminance of 15 070 cd m−2 and maximum current efficiency of 46.1 cd A−1, which is significantly higher (about 3 times) compared to devices with FA only (maximum EQE of 4.1%, maximum luminance of 4521 cd m−2) and Cs-only (maximum EQE of 4.0%, maximum luminance of 4886 cd m−2). The photoluminescence quantum yield of the Cs:FA 1:1 sample is similarly enhanced, 21.3% compared 5.4% and 6%, for FA-only and Cs-only samples, respectively. It can be observed that the Cs:FA ratio significantly affects the crystallization of the perovskite, with the optimal 1:1 ratio resulting in the formation of tetragonal Cs0.5FA0.5PbBr3 phase (different from cubic FAPbBr3 and orthorhombic CsPbBr3) with pronounced preferential orientation as well as a significant reduction in the trap density, which leads to a substantial improvement in the light-emitting performance.

Original languageEnglish
Article number2100393
JournalAdvanced Optical Materials
Issue number21
Publication statusPublished - 4 Nov 2021
Externally publishedYes


  • Ruddlesden–Popper
  • X-ray diffraction
  • green emission
  • perovskite light-emitting diodes
  • quasi-2D perovskites


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