Electroluminescence from a Conjugated Polymer Grafted with CdSe/ZnS: High Brightness and Improved Efficiency

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K.-B. Chen
M.-H. Chen
S.-H. Yang
C.-H. Hsieh
C.-S. Hsu
Chia-Chun Chen
H.-J. Chien

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A new series of sulfide-substituted poly(1,4-phenylene vinylene) derivatives (S1PPV–S3PPV) with different composition ratios were successfully synthesized via the Gilch route. The CdSe/ZnS were grafted to the sulfur atoms by ligand exchange reaction. The grafted CdSe/ZnS contents were determined from TGA analysis to be from 4.6 to 37.8%. A new peak at 1151 cm−1 formed in FT-IR after ligand exchange, which is attributed to the force formation between sulfur and CdSe. The GPC results show that the molecular weights of final polymers became higher after ligand exchange. Thin films of obtained polymers emitted bright green and yellow light with the max emission peak located from 546 to 556 nm. Double-layer LEDs with an ITO/PEDOT/polymer/Ca/Al configuration were fabricated to evaluate the potential use of these polymers. The turn-on voltages of the devices were about 4–5 V. As the CdSe/ZnS content increased in grafted polymers, the device performance was significantly enhanced as compared to pristine polymers. In the case of S3PPV, the double-layer device showed a maximum luminance of 6073 cd/m2 with a current yield of 0.82 cd/A. The maximum luminance and current yield was enhanced to 13,390 cd/m2 and 2.25 cd/A by grafting CdSe/ZnS onto polymers.