Phase-Transfer Ligand Exchange of Lead. Chalcogenide Quantum Dots for Direct Deposition. of Thick, Highly Conductive Films

Transcription

1 Phase-Transfer Ligand Exchange of Lead Chalcogenide Quantum Dots for Direct Deposition of Thick, Highly Conductive Films Qianglu Lin,, Hyeong Jin Yun,, Wenyong Liu, Hyung-Jun Song, Nikolay S. Makarov, Oleksandr Isaienko, Tom Nakotte, Gen Chen, Hongmei Luo, Victor I. Klimov, Jeffrey M. Pietryga,* Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87544, United States Department of Chemical and Materials Engineering, New Mexico State University, Las Cruces, New Mexico 88003, United States These authors contribute equally to this work. * Address correspondence to pietryga@lanl.gov S1

2 Supporting Information (a) (b) (c) PbS QDs PbSe QDs PbTe QDs Absorbance (Arb. Unit) PL Intensity (Arb. Unit) Absorbance (Arb. Unit) PL Intensity (Arb. Unit) Absorbance (Arb. Unit) PL Intensity (Arb. Unit) Wavelength (nm) Wavelength (nm) Wavelength (nm) Figure S1. Absorption (solid) and PL (dotted) spectra of various sizes of (a) PbS, (b) PbSe and (c) PbTe QDs with OLA as capping ligand. 10 (a) 0 10 (b) 0 (c) 10 0 Normalized PL Intensity PbS-OLA in TCE, t=1.73 s PbS-LiI in NMF, t 1 =0.35 s (20%), t 2 =1.22 s (80%) Time ( s) Normalized PL Intensity PbSe-OLA in TCE, t=1.49 s PbSe-LiI in NMF, t 1 =0.42 s (34%), t 2 =1.46 s (66%) Time ( s) Normalized PL Intensity PbTe-OLA in TCE, t 1 =0.096 s (34%), t 2 =1.49 s (66%) PbTe-LiI in NMF, t=1.85 s Time ( s) Figure S2. Lifetime of PbS (a), PbSe (b), and PbTe (c) before (black) and after (red) ligand exchange with LiI. S2

3 Table S1. PbS, PbSe, PbTe PL lifetime and quantum yield before and after ligand exchange with LiI. Ligand Solvent PL QY(%) Lifetime (µs)* PbS OLA TCE PbS LiI NMF PbSe OLA TCE PbSe LiI NMF PbTe OLA TCE PbTe LiI NMF *Lifetimes of QDs were extracted from Figure S2, showing the longer lifetime when the fit was biexponential. S3

4 Figure S3. High resolution TEM images of PbSe QDs passivated with (a) OLA, (b) KI, (c) LiI, (d) LiBr. S4

5 Figure S4. High resolution TEM images of PbSe QDs passivated with (a) LiSCN, (b) KSeCN (c) HCOOH, and (d) LiOOCH. S5

6 Table S2. Quantum yield and Pb:Se ratio of PbSe QD dispersions after ligand exchange with various ionic compounds, as determined by ICP-OES. Ligand PL QY (%) Pb:Se ratio OLA NH 4 I LiI NaI KI CdI PbI LiSCN (Pb:Se) 0.85 (Pb:Se+S) KSeCN LiBr LiFA S6

7 Absorbance (Arb. Unit) PbSe-OLA PbSe-LiI PbSe-PbI 2 PbSe-KSeCN Wavelength (nm) Figure S5. Absorption spectra of 4.9 nm PbSe QDs passivated with OLA (green), LiI (yellow), PbI 2 (orange), and KSeCN (red). Table S3. Hardness of various anions. Anion Hardness I Soft Br Borderline SCN - (S-coordinated) 6.4 Soft HCOO Hard S7

8 Table S4. Hardness of various cations. Cation Hardness Li Hard Na Hard K Hard Cd Soft Pb Borderline/Soft Figure S6. PL decay traces for the series of ligand-exchanged 4.9 nm PbSe QDs shown in Figure 3d. Use of PbI 2 or CdI 2 for the exchange results in very low PL QY, accompanied by the emergence of a distinct fast non-radiative decay component, suggesting very poor surface passivation in DFP solution. S8

9 (a) (b) 200 Absorbance (Arb. Unit) PbSe-OLA in TCE PbSe-NH 4 I in DFP PbSe-NH 4 I film PL Intensity (Arb. Unit) day 21 days 28 days Wavelength (nm) Wavelength (nm) Figure S7. (a)absorption spectra of 4.4 nm PbSe QDs: passivated with OLA and dispersed in TCE (green); passivated with NH 4 I and dispersed in DFP (yellow); and passivated with NH 4 I and cast as a film (red). (b) PL spectra of PbSe/NH 4 I QD film in the air for 0 day (green), 21 days (yellow), and 28 days (red). S9

10 (a) V DS = 20 V (b) V th,f = 5.56 V 0.2 V th,b = 3.02 V V GS V DS = 20 V 3 (10 3 A ) (c) V th,f = 2.66 V V th,b = 3.21 V V GS V DS = 20 V V th,f = V V th,b = V (10 3 A ) (10 3 A ) V GS Figure S8. -V GS curves of (a) PbS/LiI QDs FET, (b) PbSe/LiI QDs FET, and (c) PbTe/LiI QDs FET. V th,f and V th,b indicate the threshold voltage of forward and backward scanned - V GS characteristics, respectively. S10

11 (a) V GS = 0V 10V 20V 30V 40V (b) x10 5 6x10 5 4x10 5 2x10 5 V DS = 20 V V DS V GS Figure S9. (a) -V DS and (b) -V GS curves of PbTe/LiI QDs FET annealed at 200 C for 30 minutes. (a) V GS = 0V 10V 20V 30V 40V V DS (b) V DS = 20 V V th,f = 3.63 V V th,b = 2.91 V V GS (10 3 A ) Figure S10. (a) -V DS and (b) -V GS curves of 5.0 nm PbSe/LiI QD FET with TDP. V th,f and V th,b indicate the threshold voltage of forward and backward scanned -V GS characteristics, respectively. S11

12 Table S5. Electron mobilities for various FET devices QD Ligand Annealing Temperature ( C) Mobility (cm 2 /Vs) PbSe NH 4 Br PbSe HCOOH PbSe KSeCN PbSe KI PbSe KI+TDP PbSe LiI PbSe LiI+TDP PbSe PbI 2 +TDP PbS LiI PbTe LiI PbTe LiI+TDP S12

13 Capacitance (nf) V th V g V G Figure S11. Capacitance-Voltage plot of a film of PbI 2 exchanged 5.0 nm PbSe QDs obtained at 1kHz. The total charge injected for a given gate voltage was calculated from. Table S6. Carrier concentration of 5.0 nm PbSe QDs film with LiI, KI, and PbI 2 ligands. Ligand Carrier concentration (electron, cm -3 ) LiI KI PbI S13

14 (c) I (A) dark 13.6 W/cm 550 nm 21.8 W/cm 550 nm 25.9 W/cm 550 nm Voltage Figure S12. (a) Schematic of PbSe QD photodetector. (b) AFM line scan over an intentional scratch applied to a PbSe/NH 4 I film deposited in a single step and used in a photodetector, demonstrating a thickness of 313 nm (before top contact applied). (c) Dark current and photocurrent as a function of applied bias for the PbSe QD photodetector based on the film in under various light intensities. Figure S13. (a) AFM line scan over an intentional scratch applied to film of 4.8 nm PbSe/KI QDs, demonstrating a thickness of 5.3 m. (b) Two-dimensional AFM surface scan across the same scratched film. S14