Interface-assisted cesium-formamidinium cation exchange enables high-performance perovskite light-emitting diodes with tuneable near-infrared emissions
Zhongcheng Yuan a b, Zhangjun Hu a, Ingemar Persson a, Chuanfei Wang a, Xianjie Liu a, Chaoyang Kuang a, Weidong Xu a, Sai Bai a, Feng Gao a
a Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, SE-58183, Sweden
b Department of Physics University of Oxford Clarendon Laboratory, Oxford OX1 3PU, Reino Unido, United Kingdom
Proceedings of International Conference on Emerging Light Emitting Materials (EMLEM22)
Aspects of Emergent Light Emitters:
Limasol, Cyprus, 2022 October 3rd - 5th
Oral, Zhongcheng Yuan, presentation 064
Publication date: 15th July 2022

Achieving high-quality cesium-formamidinium lead iodide (CsxFA1-xPbI3) perovskites with widely tuneable bandgaps
is highly desired for their optoelectronic applications yet remains a challenge because of the different phase transition
behaviour of FAPbI3 and CsPbI3 perovskite during film depositions.1,2 Herein, by utilizing an alkaline-interface-assisted
cation-exchange method, we fabricate a set of highly emissive CsxFA1-xPbI3 perovskite films with fine-tuning Cs-FA
alloying ratio for emission-tuneable near-infrared light-emitting diodes (NIR-LEDs). We reveal that the deprotonation
of FA+ cations and the formation of hydrogen-bonded gels consisting of CsI and FA facilitated by zinc oxide underneath
effectively removes the Cs-FA ion-exchange barrier, promoting the formation of phase-pure CsxFA1-xPbI3 films with
emission filling the gap between that of pure Cs- and FA-based perovskites.3 The obtained NIR-LEDs with narrow
electroluminescence peaking from 715 to 780 nm simultaneously demonstrate high peak external quantum efficiencies
of over 15%, maximum radiances exceeding 300 W sr-1 m-2, and high power conversion efficiencies above 10 % at 100
mA cm-2, representing the best-performing devices based on solution-processed wavelength-tuneable NIR emitters in
the similar region4.

1 Li, Z., et.al. Chem. Mater. 28, 284-292 (2016)
2 Lee, J.-W., et.al. Adv. Energy Mater. 5, 1501310 (2015)
3 Z, Yuan., et.al. Nat. Commun 10, 2818 (2019)
4 Z, Yuan., et.al. In revision.

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