Tautomeric Mixture Coordination Enables Efficient Lead-Free Perovskite LEDs.

Lead (Pb) halide perovskite light-emitting diodes (PeLEDs) have demonstrated extraordinary optoelectronic performance 1-3 . However, potential toxicity issues with Pb 4,5 mean that 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 stabilize Pb-free TEA 2 SnI 4 (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 improves the ordering in crystal structure of TEA 2 SnI 4 . These factors give a two orders of magnitude reduction in nonradiative recombination capture coefficient and approximately 2-fold enhancement in exciton binding energy. Our Pb-free PeLED has an EQE of up to 20.29 per cent, representing a performance comparable to that of state-of-the-art Pb-containing PeLEDs 6-12 . We anticipate that these findings will provide insights into the stabilization of Sn(II) perovskites and further progress Pb-free perovskite applications.