Boosting electroluminescence performance of all solution processed InP based quantum dot light emitting diodes using bilayered inorganic hole injection layers
Qiuyan Li, Sheng Cao, Peng Yu, Meijing Ning, Ke Xing, Zhentao Du, Bingsuo Zou, Jialong Zhao
Abstract
The development of high-performance InP-based quantum dot light-emitting diodes (QLEDs) has become the current trend in ecofriendly display and lighting technology. However, compared with Cd-based QLEDs that have already been devoted to industry, the efficiency and stability of InP-based QLEDs still face great challenges. In this work, colloidal <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>NiO</mml:mi> </mml:mrow> <mml:mi>x</mml:mi> </mml:msub> </mml:mrow> </mml:math> and Mg-doped <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m2"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>NiO</mml:mi> </mml:mrow> <mml:mi>x</mml:mi> </mml:msub> </mml:mrow> </mml:math> nanocrystals were used to prepare a bilayered hole injection layer (HIL) to replace the classical polystyrene sulfonate (PEDOT:PSS) HIL to construct high-performance InP-based QLEDs. Compared with QLEDs with a single HIL of PEDOT:PSS, the bilayered HIL enables the external quantum efficiencies of the QLEDs to increase from 7.6% to 11.2%, and the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m3"> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mrow> <mml:mn>95</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> lifetime (time that the device brightness decreases to 95% of its initial value) under a high brightness of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m4"> <mml:mrow> <mml:mn>1000</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>cd</mml:mi> <mml:mtext> </mml:mtext> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> to prolong about 7 times. The improved performance of QLEDs is attributed to the bilayered HIL reducing the mismatched potential barrier of hole injection, narrows the potential barrier difference of indium tin oxide (ITO)/hole transport layer interface to promote carrier balance injection, and realizes high-efficiency radiative recombination. The experimental results indicate that the use of bilayered HILs with p-type <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m5"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>NiO</mml:mi> </mml:mrow> <mml:mi>x</mml:mi> </mml:msub> </mml:mrow> </mml:math> might be an efficient method for fabricating high-performance InP-based QLEDs.