Giant polarization facilitating ion migration in perovskite light emitting diodes: implications for performance degradation

Abstract Perovskite light emitting diodes (PeLEDs) based on metal halides are highly efficient and show high color purity. Here, we report a green PeLED based on methylammonium lead tribromide (MAPbBr 3 ) with a high brightness of 13 000 cdm −2 at 6 V with a narrow full-width half-maximum of 20 nm. Impedance spectroscopy revealed that these devices exhibit giant polarization facilitating ion-migration and, subsequently, performance degradation. Energy dispersive x-ray spectroscopy showed that the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mtext> </mml:mtext> </mml:mrow> <mml:mrow> <mml:mtext>B</mml:mtext> </mml:mrow> <mml:mrow> <mml:msup> <mml:mrow> <mml:mtext>r</mml:mtext> </mml:mrow> <mml:mo>−</mml:mo> </mml:msup> </mml:mrow> </mml:mrow> </mml:math> ions are the migrating species in this material. Using an equivalent circuit analysis, diffusion coefficient, ionic conductivity, concentration, and mobility of the migrating <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mtext>B</mml:mtext> </mml:mrow> <mml:mrow> <mml:msup> <mml:mrow> <mml:mtext>r</mml:mtext> </mml:mrow> <mml:mo>−</mml:mo> </mml:msup> </mml:mrow> </mml:mrow> </mml:math> ions have been calculated to be 3.157 × 10 −12 cm 2 s −1 , 2.44 × 10 −10 Scm −1 , 2.005 × 10 16 cm −3 , and 1.26 × 10 −10 cm 2 V −1 s −1 , respectively. These ions accumulate at the metal perovskite interface under applied field and can lead to brightness drop under long-term operation. Further, the accumulated ion concentration increases with the applied bias which accelerates device degradation.