Enhanced Stability and Linearly Polarized Emission from CsPbI3 Perovskite Nanoplatelets through A-site Cation Engineering 

Woo Hyeon Jeong1,2, Junzhi Ye2*, Jongbeom Kim3, Rui Xu4, Xinyu Shen1,5, Chia-Yu Chang2, Eilidh L. Quinn2, Hyungju Ahn6, Myoung Hoon Song3, Peter Nellist7, Henry J. Snaith5, Yunwei Zhang4, Bo Ram Lee1* and Robert L. Z. Hoye2*

1 School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon, 16419, Republic of Korea
2 Inorganic Chemistry Laboratory, University of Oxford, Oxford, OX1 3QR, United Kingdom
3 Department of Materials Science and Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919 Republic of Korea
4 School of Physics, Sun Yat-sen University, Guangzhou, 510275 China
5 Clarendon Laboratory, Department of Physics, University of Oxford, Oxford, OX1 3PU United Kingdom
6 Pohang Accelerator Laboratory (PAL) Pohang, Gyeongbuk 37673, Republic of Korea
7 Department of Materials, University of Oxford, Oxford OX1 3PH United Kingdom


Main Text: 
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Figure 1
c: Nanoplatelets solution PL and UV-Vis Absorption Spectra. Data obtained by Woo Hyeon Jeong.

Figure 2
b: In-situ PL spectra during the formation of each PeNPLs in colloidal solution. Data obtained by Woo Hyeon Jeong and Jongbeom Kim.
c: Evolution of the PL peak wavelength over time after injecting the Cs/FA oleate solution into the reaction mixture. Data obtained by Woo Hyeon Jeong and Jongbeom Kim.

Figure 3
a: Integrated PL intensity of colloidal PeNPL solutions as a function of time stored at 80 ℃ in ambient air. Data obtained by Woo Hyeon Jeong.
b: Change in the normalized PLQY of PeNPL thin films. Data obtained by Woo Hyeon Jeong.

Figure 4
a: Power density-dependent a PLQY of colloidal PeNPLs. Data obtained by Woo Hyeon Jeong and Xinyu Shen.
b: Power density-dependent integrated PL peak intensity of colloidal PeNPLs. Data obtained by Woo Hyeon Jeong and Xinyu Shen.
c: Time-resolved PL decay curve of colloidal PeNPLs. Data obtained by Woo Hyeon Jeong and Xinyu Shen.
d: 1H-NMR spectra of colloidal PeNPLs dispersed in deuterated toluene. Data obtained by Woo Hyeon Jeong and Eilidh L. Quinn.
e-f DFT-calculated binding energy of each ligands on the surface of PeNPLs surface. Data obtained by Rui Xu.

Figure 5
b-c: Polarization dependence of the normalized PL intensity of PeNPL films. Data obtained by Woo Hyeon Jeong.

Supplementary Information
Figure S2
a-d: Size distribution histogram of each PeNPLs determined from TEM measurements. Data obtained by Woo Hyeon Jeong and Chia-Yu Chang.

Figure S3
Distribution in the aspect ratio of PeNPLs. Data obtained by Woo Hyeon Jeong and Chia-Yu Chang.

Figure S4
PL spectra of each PeNPL films. Data obtained by Woo Hyeon Jeong.

Figure S5
X-ray diffraction patterns of PeNPLs Data obtained by Woo Hyeon Jeong.

Figure S6
In-situ PL spectra during the formation of each PeNPL following the injection of the Cs-oleate/FA-oleate into the PbI2-ligand solution. Data obtained by Woo Hyeon Jeong and Jongbeom Kim.

Figure S7
In-situ PL spectra during the formation of FAPbI3 PeNPLs. Data obtained by Woo Hyeon Jeong and Jongbeom Kim.

Figure S8
PL spectra of colloidal PeNPL solutions of each PeNPLs heated to 80 °C as a function of time 0 to 240 min. Data obtained by Woo Hyeon Jeong.

Figure S9
N/Pb ratios from XPS measurements of each PeNPLs before and after aging. Data obtained by Woo Hyeon Jeong and Jongbeom Kim.

Figure S10
XPS spectra of each PeNPLs. Data obtained by Woo Hyeon Jeong and Jongbeom Kim.

Figure S11
1H-NMR spectra of each PeNPLs before and after aging. Data obtained by Woo Hyeon Jeong and Jongbeom Kim.

Figure S12
Change in the X-ray diffraction patterns of each PeNPL films over time after storage in ambient conditions. Data obtained by Woo Hyeon Jeong.

Figure S13
PLQY distributions of collidal PeNPLs. Samples were measured by Quantaurus-QY Absolute PL quantum yield spectrometer (HAMAMATSU). Data obtained by Jongbeom Kim.

Figure S14 
Change in the PL spectra of colloidal PeNPLs depending on excitation power densities. Data obtained by Woo Hyeon Jeong and Xinyu Shen.

Figure S15
1H-NMR spectra of colloidal PeNPLs dispersed in deuterated toluene. Data obtained by Woo Hyeon Jeong and Eilidh L. Quinn.

Figure S17-18
Polarization dependence of the normalized PL intensity of PeNPL films. Data obtained by Woo Hyeon Jeong.






