Lead (Pb) halide perovskite light-emitting diodes (PeLEDs) have demonstrated extraordinary optoelectronic performance 1-3 . However, the toxicity of Pb has raised as a serious concern 4,5 .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 6-8 . We anticipate that these findings will provide insights into the stabilization of Sn(II) perovskites and inspire researchers to pioneer Pb-free perovskite applications.
The lagging development of deep-blue perovskite light-emitting diodes (PeLEDs) heavily impedes their practical applications in full-color display due to the absence of spectrally stable emitters and the mismatch of carrier injection capacity. Herein, we report highly efficient deep-blue PeLEDs through a new chemical strategy that addresses the dilemma for simultaneously constant electroluminescence (EL) spectra and high-purify phase in reduced-dimensional perovskites. The success lies in the control of adsorptionenergy differences between phenylbutylamine (PBA) and ethylamine (EA) interacting with perovskites, which facilitates narrow n-value distribution. This approach leads to an increased exciton binding energy and enhanced surface potential, hence improving radiative recombination. As a result, an external quantum efficiency of 4.62 % is achieved in PeLEDs with a stable EL peak at 457 nm, demonstrating the best reported result for deep-blue PeLEDs so far.
Power conversion efficiency (PCE) and stability of tin perovskite solar cells (TPSCs) are major concerns in developing lead-free photovoltaics. Photovoltaic performance of TPSCs often suffers from the oxidation of Sn 2þ , organic degradation, and ion migration, which inevitably cause plenty of trap states and render inferior device parameters. Herein, a natural ascorbic acid is first introduced for high-performance TPSCs as a multifunctional reductant to suppress the oxidation of Sn 2þ and regulate trap states accordingly. Interestingly, it is found that the ascorbic acid reduces Sn 4þ to Sn 2þ by C═C double bonds and forms a complex with Cs 0.05 FA 0.95 SnI 3 perovskites via strong hydrogen bonding interactions. By virtue of theoretical calculations, the mechanism of the ascorbic acid role is further clarified. Apart from effective passivation and suppressing trap density, a superoxide interaction between perovskite and ascorbic acid is proposed. The existence of ascorbic acid successfully improved the energy barrier for O 2 À generation. As a result, a significantly improved PCE from 8.95% to 13.32% is achieved for Cs 0.05 FA 0.95 SnI 3 TPSCs with 0.5% ascorbic acid incorporation under AM 1.5 G illumination. In addition, our devices maintain 90% value of initial PCE after 500 h storage.
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