Potassium Iodide Passivation Enabling Performance Improvement of CsCu₂I₃-Based LEDs

Ternary copper halide CsCu<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {{2}}}$ </tex-math></inline-formula>I<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {{3}}}$ </tex-math></inline-formula> emerges as a highly promising candidate for eco-friendly light-emitting diodes (LEDs), but the electroluminescent performance is limited by defect-related nonradiative losses and disordered crystallization. Herein, we develop a potassium iodide (KI)-modified engineering of CsCu<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {{2}}}$ </tex-math></inline-formula>I<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {{3}}}$ </tex-math></inline-formula> emitters to passivate the defects by compensating for any halide vacancies, and reduce trap state density. Meanwhile, this strategy can optimize the crystallization process of CsCu<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {{2}}}$ </tex-math></inline-formula>I<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {{3}}}$ </tex-math></inline-formula> to obtain continuous high-quality CsCu<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {{2}}}$ </tex-math></inline-formula>I<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {{3}}}$ </tex-math></inline-formula> films, which is conductive to suppressing leakage current of corresponding devices. Benefitting from the suppression of nonradiative recombination due to the reduced halide vacancies, and improved film morphology of CsCu<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {{2}}}$ </tex-math></inline-formula>I<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {{3}}}$ </tex-math></inline-formula> by optimizing the crystallization process of CsCu<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {{2}}}$ </tex-math></inline-formula>I<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {{3}}}$ </tex-math></inline-formula>, the EQE of corresponding LED is largely improved from 0.02% to 0.065%. The results highlight the great potential of KI passivation for high performance eco-friendly CsCu <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {{2}}}$ </tex-math></inline-formula>I<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathbf {{3}}}$ </tex-math></inline-formula> based LED.