Tautomeric Mixture Coordination Enables Efficient Lead-Free Perovskite LEDs

Lead (Pb) halide perovskite light-emitting diodes (PeLEDs) have demonstrated extraordinary optoelectronic performance. However, the toxicity of Pb has raised as a serious concern. Removing Pb from the best-performing PeLEDs without compromising their excellent external quantum efficiencies (EQEs) remains a challenge. Here we report a tautomeric mixture coordination-induced electron localization strategy to fundamentally stabilize Pb-free TEA2SnI4 (TEAI, 2-thiophenethylammonium iodide) perovskite by incorporating cyanuric acid (CA). We demonstrate that a crucial function of the coordination is to amplify electronic effects and even extend to Sn atoms without strong bonding with CA, due to the formation of H-bonded tautomeric dimer and trimer superstructures on the perovskite surface. This electron localization weakens adverse effects from Anderson localization and contributes to more ordered and stable crystal structure in the resultant TEA2SnI4, which synergistically improve the perovskite with two orders of magnitude reduction in nonradiative recombination capture coefficient and about 2-fold enhancement in exciton binding energy. Levering by the interactional profit, our target Pb-free PeLED demonstrated an EQE of up to 20.13 per cent, representing a performance comparable to that of state-of-the-art Pb-containing PeLEDs. We anticipate that these findings will provide insights into the stabilization of Sn(II) perovskites and inspire researchers to pioneer Pb-free perovskite applications.