Growth of Nanosized Single Crystals for Efficient

Transcription

1 Supporting Information Growth of Nanosized Single Crystals for Efficient Perovskite Light-Emitting Diodes Seungjin Lee,, Jong Hyun Park,, Yun Seok Nam, Bo Ram Lee,, Baodan Zhao, Daniele Di Nuzzo, Eui Dae Jung, Hansol Jeon, Ju-Young Kim, Hu Young Jeong, Richard H. Friend, Myoung Hoon Song,* School of Materials Science and Engineering, Ulsan National Institute of Science and Technology, UNIST-gil 50, Ulsan, 44919, Republic of Korea. Cavendish Laboratory, JJ Thomson Avenue, Cambridge, CB3 0HE, United Kingdom. UNIST Central Research Facilities, Ulsan National Institute of Science and Technology, UNIST-gil 50, Ulsan, 44919, Republic of Korea. Department of Physics, Pukyong National University, 45 Yongso-ro, Nam-Gu, Busan 48513, Republic of Korea. 1

2 Crystal growth mechanism with benzylamine (PMA). Although heterogeneous nucleation may be a more reasonable description of our system, we use the equations for homogenous nucleation for simplicity. The free energy change of nucleation as a function of the particle radius r is given by G r = 4 3 πr3 G v + 4πr 2 γ SL Where G v and γ SL describe the free energy change associated with the liquid-to-solid transformation and the solid/liquid interfacial energy, respectively. From this equation, the critical free energy of nucleation and critical nucleus size can be obtained. The critical free energy of nucleation is given by The critical nucleus size is given by G = 16πγ SL 3 3( G v ) 2 r = 2γ SL G v Decreasing the surface energy of the nuclei means that the critical free energy of nucleation and critical nucleus size decrease. 1 Nuclei can hence be more easily generated by reducing their surface energies. The addition of PMA decreases the critical free energy of nucleation and critical nucleus size by reducing the nucleus surface energy. Furthermore, PMA retards crystal growth by capping the nuclei. This combined effect not only effectively reduces the MAPbBr 3 crystal size but also enhances its crystallinity; more cubic-shaped crystals were grown because the precursors had enough time to react with the favorable lattice points. Temperature and grain size 2

3 Crystal growth is related to the temperature of the surroundings. High temperatures give more energy to promote mass transfer and surface integration during crystal growth, resulting in a high crystal growth rate. The MAPbBr 3 film fabricated with 0.5 vol.% PMA at a low temperature showed a smaller average crystal size of 31.7 nm than the equivalent high-temperature case (81.6 nm). Thickness optimization of the TPBi electron transport layer (ETL) TPBi is an ETL that can act as a hole-blocking layer due to its deep highest occupied molecular orbital level. The electron transport and hole-blocking properties should be optimized to maximize the recombination of charge carriers. By varying the TPBi thickness (in 5 nm increments), the device efficiency, luminance, and running voltage was changed. PeLEDs with an optimized thickness of 55 nm exhibited the maximum luminance and efficiency with balanced charge carriers (Figure S7). EL blinking mechanism Even though the detailed mechanism of EL blinking has not yet been fully understood, several models have been suggested. One model involves Auger recombination related to electronic trapping. Some researchers have reported that Auger recombination occurs between photogenerated electron hole pairs and charges located in the electronic trap. 2-4 In addition, other researchers have ascribed the blinking phenomenon to the photoinduced activation and deactivation of electronic trap sites. 5-7 Both mechanisms are closely related to electronic trap sites, which are normally associated with defects. To eliminate the EL blinking of PeLEDs, defects in the perovskite materials should therefore be suppressed. Our method enables defectfree nanosized single crystals to be grown, coupled with the passivation of the surface defects, 3

4 through the PMA ligand. As a result, the PeLED prepared with the optimized condition (0.5 vol.% PMA and low temperature) showed no EL blinking (Movie S1). Trap density calculation Figure S6 showed the current-voltage characteristics for the hole-only device with and without PMA. At low voltages (< V TFL ), the linear J-V relation (red line) indicates an ohmic response. A trap-filling region (blue line) was identified by abruptly increase of the current injection at a voltage (> V TFL ) where all the traps are filled. From this region, the trap density was calculated using following relation. 8,9 n t = 2V TFLεε 0 el 2 where V TFL is the trap-filled limit voltage, is relative dielectric constant (25.5 for MAPbBr 3 ), 10 0 is the vacuum permittivity, e is the electron charge, and L is the thickness of the MAPbBr 3 (~ 200 nm). V TFL of MAPbBr 3 with PMA (0.65 V) is lower than that without PMA (1.05 V) (Figure S6), which indicates reduction in trap density of perovskite with PMA treatment. The trap densities were calculated to be cm -3 for MAPbBr 3 without PMA and cm -3 for MAPbBr 3 with PMA. 4

5 Figure S1. Schematic illustrations of the MAPbBr 3 film formation with and without PMA in the anti-solvent at different temperatures. Film formation (a) without PMA at high temperatures, (b) with PMA at high temperatures, and (c) with PMA at low temperatures. 5

6 Figure S2. Schematic illustrations of the different MAPbBr 3 crystal shapes. Schematics of (a) the 3D cubic structure, (b) the 2D layered structure, and (c) the 3D rod-like structure. 6

7 Figure S3. SEM images of the MAPbBr 3 films fabricated without PMA (Ref.) and with various PMA concentrations at low temperatures. 7

8 Figure S4. Variations in the grain size distributions of the MAPbBr 3 films prepared with 0.5 vol.% PMA at different temperatures. (a,b) SEM image and grain size distribution of the film fabricated at a high temperature. (c,d) SEM image and grain size distribution of the film fabricated at a low temperature. 8

9 Figure S5. FT-IR spectra of PMA and the MAPbBr 3 films prepared with and without PMA. FT- IR spectra over ranges of (a) cm 1, (b) cm 1, and (c) cm 1. 9

10 Figure S6. J-V characteristics of hole-only device (ITO/Perovskite/Au). J-V characteristic of hole only device (a) without PMA and (b) with PMA. 10

11 Figure S7. Performance of the PeLED devices prepared under the optimized conditions with different thicknesses of the ETL. (a) Current density versus voltage (J V), (b) luminance versus voltage (L V), (c) current efficiency versus current density (CE J), and (d) external quantum efficiency versus current density (EQE J) characteristics of PeLEDs fabricated with 0.5 vol.% PMA at low temperatures with different ETL thicknesses. 11

12 Figure S8. J-V characteristics of hole-only device (ITO/PEDOT:PSS/MAPbBr 3 /Poly- TPD/MoO 3 /Au) and electron-only device (ITO/ZnO/MAPbBr 3 /TPBi/LiF/Al) prepared under the optimized conditions with different thicknesses of TPBi. 12

13 Figure S9. Differences in the performance of PeLED devices and PLQYs of perovskite films prepared at different temperatures. (a) J V, (b) L V, (c) CE J, and (d) EQE J characteristics of PeLEDs and (e) PLQYs of perovskite films fabricated with 0.5 vol.% PMA at different temperatures. 13

14 Figure S10. Operational stability of PMA-free and PMA-treated PeLEDs with encapsulation measured at current density of 5 ma cm -2 under ambient conditions as function of operation time. 14

15 Figure S11. PeLED hysteresis curves. J V characteristics of PeLEDs prepared (a) without PMA and (b) with 0.5 vol.% PMA at a scan speed of 0.3 V s 1. 15

16 Table S1. Summarized PL lifetime of MAPbBr 3 films with and without different concentration of PMA. Film configuration avr [ns] 2 Glass / perovskite (Ref.) Glass / perovskite (PMA 0.25 vol. %) Glass / perovskite (PMA 0.50 vol. %) Glass / perovskite (PMA 1.00 vol. %) Glass / perovskite (PMA 2.00 vol. %) Glass / perovskite (PMA 4.00 vol. %)

17 Table S2. Summarized device performance of PeLEDs with different thickness of TPBi. Device configuration (PeLEDs) Luminance max [cd/m 2 bias CE max bias EQE max bias Turn-on voltage 0.1 cd/m 2 ITO / PEDOT:PSS / MAPbBr 3 (PMA 0.50 vol. % in CB) / TPBi (50 nm) / LiF / Al ITO / PEDOT:PSS / MAPbBr 3 (PMA 0.50 vol. % in CB) / TPBi (55 nm) / LiF / Al ITO / PEDOT:PSS / MAPbBr 3 (PMA 0.50 vol. % in CB) / TPBi (60 nm) / LiF / Al ITO / PEDOT:PSS / MAPbBr 3 (PMA 0.50 vol. % in CB) / TPBi (70 nm) / LiF / Al 5.6 V 4.8 V 4.8 V V 5.0 V 5.0 V V 5.4 V 5.4 V V 6.2 V 6.2 V

18 Table S3. Summarized device performance of PeLEDs with different temperature. Device configuration (PeLEDs) Luminance max [cd/m 2 bias CE max bias EQE max bias Turn-on voltage 0.1 cd/m 2 ITO / PEDOT:PSS / MAPbBr 3 (PMA 0.50 vol. % in CB) / TPBi / LiF / Al (20~25 o C) ITO / PEDOT:PSS / MAPbBr 3 (PMA 0.50 vol. % in CB) / TPBi / LiF / Al (15~20 o C) ITO / PEDOT:PSS / MAPbBr 3 (PMA 0.50 vol. % in CB) / TPBi / LiF / Al (10~15 o C) 5.8 V 5.0 V 5.0 V V 41.3@ 5.0 V 9.0@ 5.0 V V 5.0 V 5.0 V

19 Table S4. Comparison of our work with previous reports. Previous reports Publication year/month Emission layer Maximum CE (cd A -1 ) Maximum EQE (%) Wavelength (nm) Xiao et al /01 MAPbI nm Xiao et al /01 MAPbBr nm Lee et al /03 MAPbBr nm Kim et al /02 Cs 10( MA 0.17 FA 0.83 ) 90 PbBr 0.33 I 2.67 Not reported nm Cho et al /12 MAPbBr ~540 nm Wang et al /11 (NMA)FA 0.5 PbI 2 Not reported nm Zhang et al /06 Cs 0.87 MA 0.13 PbBr ~525 nm Zhang et al /07 CsPbI nm 19

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