2D Perovskite matrices to stabilize NIR quantum dots

April 07, 2017 // By Julien Happich
Publishing their work in the ACS Photonics journal in a paper titled "Quantum Dots in Two-Dimensional Perovskite Matrices for Efficient Near-Infrared Light Emission", an international team of researchers has made incremental progress in the preparation of Near InfraRed (NIR) quantum dot based LEDs.

As the researchers explain in their paper, solution-processed QD-based LEDs employ a double heterojunction architecture in which the emissive QD layer is sandwiched between an electron transport layer (ETL) and a hole transport layer (HTL). Although NIR QD solutions have been demonstrated with luminescence efficiencies reaching about 40%, their overall photoluminescence quantum efficiency (PLQE) is much lower due to non-radiative recombination and the dissociation of charge carriers at surface defects and material interfaces.

Improving on prior art strategies to prevent these self-quenching effects, they moved away from core−shell quantum dots embedded in a 3D organolead halide perovskite matrix (which suffers from low stability to heat and moisture) to embedding the QDs into more stable two-dimensional perovskites. The 2D perovskite passivation, as they describe the stabilization process, is achieved via an in situ alkylammonium/alkylamine substitution carried out during the quantum dot (QD) ligand exchange process where the longer carbon backbones breaks the symmetry of the 3D structure and introduces two-dimensional (2D) structuring that produces a perovskite structure more resilient to moisture and irradiation.

They then prepared dot-in-2D-perovskite thin films by spin-casting a solution containing QDs and perovskite precursors, and created QD-based LEDs which exhibited external quantum efficiency (EQE) peak values up to 2% and radiances of about 1 W sr 1 m 2. They also found that the devices maintained a high performance (radiance >0.7 W sr 1 m 2) at operation voltages up to 7.5 V, a 1.7 fold improvement over the previous dot-in-3D-perovskite LEDs which would typically break down under a 4.5V bias.

The active layer film could also be made much thinner, with an average roughness reduced from 31nm for the first-generation films to 3.0nm for films based on the novel 2D Perovskite approach, potentially reducing materials consumptions 10-fold.