Polymer light emitting diodes based on diblock copolymer

• Main Authors: Jin-Cheng Zhang, 張晉誠
• Other Authors: Chia-Chen Hsu
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/95440704138664802238

碩士 === 國立中正大學 === 物理所 === 95 === -b-PI層的結構，亮度高出1.6倍、效率高出1.44倍。 Abstract Various physical properties of a polystyrene-b-polyisoprene diblock copolymer chemisorption with gold nanoparticles (PS-b-PI-Au) and a polystyrene-b-polyisoprene (PS-b-PI) diblock copolymer were investigated, and the results were used to study the feasibility of empolying the polymer thin film as a hole-block interlayer for a polymer light emitting diode (PLED) device. The design of blue PLED divice studied in this work was structured with the layout ITO/PEDOT/PS-b-PI or PS-b-PI-Au/PFO/Ca/Al, in which ITO was used as an anode, Ca/Al as a cathode, PEDOT as a polymeric hole transporting layer, and PFO as an emitting layer. Studies of adding differnet concentrations of PS-b-PI-Au layer bewteen PEDOT and PFO revealed that although the added interlayer increased electron-hole recombination rate, it decreased electron-hole injection rate as well. There are two possible casuses for this problem: (1) a non-uniform and rough surface from the size effect of nanogold paricles leads to an increase of resisteance and a decrease of current of the device; (2) an increase of current passing through the added interlayer results in a decrease in device current at the same applied voltage. The possible causes for the decrease of luminous efficieny include (1) a decrease in numbers of electron-hole pairs from the fast recominbation rate leading to a decrese of luminescence of the device, and (2) an increase of the emitting light through the added interlayer resulting in a decrease of overall luminescence. The similar studies of adding differnet concentrations of PS-b-PI layer bewteen PEDOT and PFO show that PS-b-PI layer can prevent the fast recombination of excitons at the PEDOT interface, which results in a larger increase in the luminous and current efficiency of the devices. Measured energy gap of PS-b-PI thin film indicated that it can be empolyed as a hole-blcokinb layer. Absorption spectra of the PS-b-PI thin film show that no visible light was found to emit from this layer. The maximum brightness and the maximum current efficiency of the PLED device, using 1.5 wt% PS-b-PI, are found to be 4922(cd/m2) and 1.30 (cd/A), respectively, exhibiting a 1.6 times of brightness and a 1.44 times of current efficiency than that of PLED without a PS-b-PI layer. The preliminary results presented here indeed demonstrate that PS-b-PI can be used as a hole-block layer to improve the luminous efficiency and lifetime performance.