Tautomeric mixture coordination enables efficient lead-free perovskite LEDs.

Lead halide perovskite light-emitting diodes (PeLEDs) have demonstrated remarkable optoelectronic performance1-3. However, there are potential toxicity issues with lead4,5 and removing lead from the best-performing PeLEDs-without compromising their high external quantum efficiencies-remains a challenge. Here we report a tautomeric-mixture-coordination-induced electron localization strategy to stabilize the lead-free tin perovskite TEA2SnI4 (TEAI is 2-thiopheneethylammonium iodide) by incorporating cyanuric acid. We demonstrate that a crucial function of the coordination is to amplify the electronic effects, even for those Sn atoms that aren't strongly bonded with cyanuric acid owing to the formation of hydrogen-bonded tautomeric dimer and trimer superstructures on the perovskite surface. This electron localization weakens adverse effects from Anderson localization and improves ordering in the crystal structure of TEA2SnI4. These factors result in a two-orders-of-magnitude reduction in the non-radiative recombination capture coefficient and an approximately twofold enhancement in the exciton binding energy. Our lead-free PeLED has an external quantum efficiency of up to 20.29%, representing a performance comparable to that of state-of-the-art lead-containing PeLEDs6-12. We anticipate that these findings will provide insights into the stabilization of Sn(II) perovskites and further the development of lead-free perovskite applications.

Deep-Blue Electroluminescence of Perovskites with Reduced Dimensionality Achieved by Manipulating Adsorption-Energy Differences.

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 adsorption-energy 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.

Growing MASnI3perovskite single-crystal films by inverse temperature crystallization.

Perovskite single-crystal films are promising candidates for high-performance perovskite optoelectronic devices due to their optoelectrical properties. However, there are few reports of single-crystal films of tin based perovskites. Here, for the first time, we realize the controllable growth and preparation of lead-free tin perovskite MASnI3single crystals via inverse temperature crystallization (ITC) strategy with γ-butyrolactone (GBL) as solvent. The solubility characteristics of MASnI3in GBL are clarified by quantitative analytical method. Highly repeatability experiments are further demonstrated using this unique solubility and ITC properties. Sequentially, using space limiting method, tin perovskite MASnI3single-crystal thin films are fabricated with micron-scale thickness, which is highly desired for efficient tin perovskite solar cells. Our MASnI3single-crystal thin films show typical single-crystalline features including strongly optical absorbance with sharp absorption edges, pure-phase x-ray diffraction patterns, and absence of Sn(IV) x-ray photoelectron spectroscopy. We believe that our findings will further broaden the application prospects of tin perovskite MASnI3single crystals and cause a new upsurge in exploring the field of lead-free perovskite single-crystal growth.