Supporting Information

Transcription

1 Supporting Information Highly Efficient Blue Phosphorescent Organic Light-Emitting Diodes Employing a Host Material with Small Bandgap Lei Zhang, Ye-Xin Zhang, Yun Hu, Xiao-Bo Shi, Zuo-Quan Jiang, Zhao-Kui Wang*, and Liang-Sheng Liao* Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices Institute of Functional Nano & Soft Materials (FUNSOM) Soochow University Suzhou , China lsliao@suda.edu.cn; zkwang@suda.edu.cn; S-1

2 Table of Contents Figure S1. 1 H NMR spectrum of DBF-DMS. Figure S2. 13 C NMR spectrum of DBF-DMS. Figure S3. TGA traces of DBF-DMS at a heating rate of 10 o C /min. Figure S4.UPS spectrum of DBF-DMS. Figure S5. PL transient decay curve of mcp and DBF-DMS film. Figure S6. The EL spectra of device B1 and B2 at different current densities. Figure S7. Hole only and electron only devices based on mcp and DBF-DMS. Figure S8. (a) The current density versus voltage characteristics; (b) PE-luminance characteristics of the devices with different host. Figure S9. (a) Lifetimes and (b)changes in operating voltage of device B1, and B2 with an initial brightness of 1000 cd/m 2. Figure S10. Exciton density profile in the EMLs of device B1 and B2. Figure S11. Polarized optical microscopic images of mcp and DBF-DMS after annealing. Figure S12. (a) The current density and luminance versus voltage characteristics; (b) CE-luminance characteristics of device B2, and T1. Figure S13. The electroluminescent (EL) spectra of device W1 and W2. Figure S14. Cyclic voltammograms of the (a) mcp and (b) DBF-DMS scanned fourtimes. Figure S15. The photoluminescence quantum yield measurements for DBF-DMS and mcp:dbf-dms 10 vol.% films. Figure S16. The photoluminescence quantum yield measurements of DBF-DMS in solution. Table S1. Device characteristics in DBF-DMS and mcp based white PhOLEDs. References S-2

3 Figure S1. 1 H NMR spectrum of DBF-DMS. S-3

4 Figure S2. 13 C NMR spectrum of DBF-DMS. S-4

5 Figure S3. TGA traces of DBF-DMS at a heating rate of 10 o C/min. S-5

6 Figure S4.UPS spectrum of DBF-DMS. S-6

7 Figure S5. PL transient decay curve of mcp and DBF-DMS film. To confirm if DBF-DMS possess TADF character in such a small E ST, the transient PL decay of the film of DBF-DMS was investigated in vacuum. The transient PL decay of the film of mcp was also measured for comparison. The energy transfer processes in these films are almost the same according to their transient behaviors. As shown in Figure, there are no TADF delayed parts in the transient decay curves of mcp and DBF-DMS. The average lifetime of mcp and DBF-DMS are 2.0 ns and 7.3 ns. From the short lifetime, there are no TADF properties existed in mcp and DBF-DMS. S-7

8 Figure S6. The EL spectra of device B1 and B2 at different current densities. S-8

9 Figure S7. Hole only and electron only devices based on mcp and DBF-DMS. Device structure: Hole only devices: ITO/MoO 3 (10 nm)/ mcp (or DBF-DMS) (100 nm)/ MoO 3 (10 nm) /Al (100 nm). Electron only devices: ITO/ Bphen:Li (10 nm) 1 vol.% (10 nm)/ mcp (or DBF-DMS) (100 nm)/bphen:li (10 nm) 1 vol.% /Al (100 nm). DBF-DMS based hole- and electon-only devices show higher current densities at the same voltage than mcp based ones. In short, DBF-DMS has both better hole and electron transporting abilities than mcp. This makes device B2(DBF-DMS) a lower driving voltage than device B1(mCP). S-9

10 Figure S8.(a) The current density versus voltage characteristics; (b) PE-luminance characteristics of the devices with different host. Device structure: ITO/HAT-CN (10 nm)/tapc (45 nm)/mcp(x vol.%): DBF-DMS(88-x vol.%): fac-ir(iprpmi) 3 12 vol.% (20 nm) /TmPyPB (45 nm)/liq (2 nm)/al (100 nm), x=88, 70, 50, and 0, respectively. Devices with higher ratio of DBF-DMS in the EML have reletively lower driving voltage and higher power efficiency. This means an improved carrier injection and transporting ability can be achieved by DBF-DMS. S-10

11 Figure S9. (a) Lifetimes and (b)changes in operating voltage of device B1, and B2 with an initial brightness of 1000 cd/m 2. S-11

12 Figure S10. Exciton density profile in the EMLs of device B1 and B2. Device structure: ITO/HAT-CN (10 nm)/tapc (45 nm)/host: fac-ir(iprpmi) 3 12 vol.% (x nm)/host: Ir(MDQ) 2 acac2 vol.% (1 nm)/host: fac-ir(iprpmi) 3 12 vol.% (19-x nm)/tmpypb (45 nm)/liq (2 nm)/al (100 nm), x=0, 6, 12, and 19, respectively. To determine the exciton distribution in the emission zones of device B1 and B2, a series of PHOLEDs(8 devices) with sensing layers were fabricated. Here, a red dopant, iridium(iii)bis-(2-methyldibenzo[f,h]quinoxaline)(acelylacetonate) (Ir(MDQ) 2 acac) is co-doped with the hosts at 2 vol% at different positions(55, 62, 68, and 75 nm away from the anode) in the EMLs of device B1 and B2 to form sensing layer of 1nm. The relative emission intensity of 600 nm by Ir(MDQ) 2 acac can reflect the distribution of excitons in the EML. Utilizing the method that has been reported 1, exciton density profilein the EMLs of device B1 and B2 was measured to confirm the recombination zone, which is highly related to the lifetime of the device. However, exciton density profilein the EMLs of device B1 and B2 show similar tendency. A weak difference between the recombination zones shouldn t be the main reason for the different lifetime (Figure S10, Supporting Information). S-12

13 Figure S11. Polarized optical microscopic images of mcp and DBF-DMS after annealing. Figure S11 shows the polarized optical microscopic images of mcp and DBF-DMS films (50 nm on quartz plates) after annealing at 60 C for 50 h. The device degradation can be caused by crystallization. 2-3 The film of mcp shows serious crystalization, which is corresponding with its low T g (60 C). 4 While there is almost no crystalization of DBF-DMS, which reveals that DBF-DMS has better stability than that of mcp. This makes the DBF-DMS based device B2 a better stability. S-13

14 DBF-DMS Based Tandem (two-units) Blue PhOLEDs. Device structure (T1): ITO/HAT-CN (10 nm)/tapc (45 nm)/dbf-dms: fac-ir(iprpmi) 3 12 vol.% (20 nm)/tmpypb (45 nm)/bphen:li (10 nm)1 vol.%/hat-cn (10 nm)/tapc (45 nm)/ DBF-DMS: fac-ir(iprpmi) 3 12 vol.% (20 nm)/tmpypb (50 nm)/liq (2 nm)/al (100 nm). Figure S12. (a) The current densityand luminance versus voltage characteristics; (b) CE-luminance characteristics of device B2, and T1. Tandem structure is a good methode to enhance both the current efficiency and stability of OLEDs 5. To take advantage of this excellent material DBF-DMS and further increase the efficiency, tandem device T1 was fabricated as shown in Figure S8. Here Bphen:Li (10 nm) 1 vol.%/hat-cn (10 nm) is utilized as intermedia connector 6. At 1000 cd/m 2, device T1 achieved an ultra high current efficiencyof cd/a, and anextremely high external quantum efficiency of 45.6 %. S-14

15 DBF-DMS and mcp Based White PhOLEDs. Device structure: ITO/HAT-CN (10 nm)/tapc (45 nm)/host: fac-ir(iprpmi) 3 12 vol.%: PO-01 1 vol.% (20 nm)/tmpypb (50 nm)/liq (2 nm)/al (100 nm). (W1:Host=mCP; W2:Host=DBF-DMS) Figure S13.The electroluminescent (EL) spectra of device W1 and W2. S-15

16 Figure S14. Cyclic voltammograms of the (a) mcp and (b) DBF-DMS scanned fourtimes. The new small peak at 0.7 V may be an electrochemical reduction reaction for an acridine part. From this point, DBF-DMS is not so electrochemical stable. And during the electrochemical oxidation process of mcp, much more obvious new peaks appearance from fist scan to fourth scan. So maybe both of host materials are not electrochemical stable. In addition, the CV behavior only reflects the stability of the organo-cation in the presence of the counter anion. It cannot be elaborated to the material stability in the device. S-16

17 Figure S15. The photoluminescence quantum yield measurements for DBF-DMS and mcp:dbf-dms 10 vol.% films. We measured the photoluminescence quantum yields by using an integrating sphere apparatus. However, the PL intensity was too weak to be detected in both neat DBF-DMS film and doped film (Figure S15). S-17

18 Figure S16. The photoluminescence quantum yield measurements of DBF-DMS in solution. Then we further measured the photoluminescence quantum yields of DBF-DMS in solution. The photoluminescence quantum yields of DBF-DMS was estimated to be 10.6% in dichloromethane using 9,10-diphenylanthracene as a standard (Φf = 0.90 in cyclohexane) (Figure S16). S-18

19 Table S1. Device characteristics in DBF-DMS and mcp based white PhOLEDs. Device V (V) a) PE(lm/W) b) CE (cd/a) b) EQE (%) b) CIE c) CRI d) W1 (mcp) , , , 14.2 (0.33, 0.48) 47.7 W2 (DBF-DMS) , , , 22.2 (0.33, 0.48) 48.6 a) Driving voltage at 1000 cd/m 2 ; b) Efficiencies in the order of maximum, and at 1000 cd/m 2. c) CIE at 1000 cd/m 2 ; d) CRI at 1000 cd/m 2. S-19

20 References 1. Zhang, Y.; Lee, J.; Forrest, S. R., Tenfold Increase in the Lifetime of Blue Phosphorescent Organic Light-Emitting Diodes. Nat. Commun. 2014, 5, Zhang, L.; Dong, S.-C.; Gao, C.-H.; Shi, X.-B.; Wang, Z.-K.; Liao, L.-S., Origin of Improved Stability in Green Phosphorescent Organic Light-Emitting Diodes Based on a Dibenzofuran/Spirobifluorene Hybrid Host. Applied Physics A 2015, 118 (1), Sun, M.-C.; Jou, J.-H.; Weng, W.-K.; Huang, Y.-S., Enhancing the Performance of Organic Light-Emitting Devices by Selective Thermal Treatment. Thin Solid Films 2005, 491 (1 2), Sasabe, H.; Toyota, N.; Nakanishi, H.; Ishizaka, T.; Pu, Y. J.; Kido, J., 3, 3 Bicarbazole Based Host Materials for High Efficiency Blue Phosphorescent OLEDs with Extremely Low Driving Voltage. Adv. Mater. 2012, 24 (24), Liao, L. S.; Slusarek, W. K.; Hatwar, T. K.; Ricks, M. L.; Comfort, D. L., Tandem Organic Light-Emitting Diode using Hexaazatriphenylene Hexacarbonitrile in the Intermediate Connector. Adv. Mater. 2008, 20 (2), Liao, L. S.; Klubek, K. P., Power Efficiency Improvement in a Tandem Organic Light-Emitting Diode. Appl. Phys. Lett. 2008, 92 (22), S-20