Lead-Free Organic–Perovskite Hybrid Quantum Wells for Highly Stable Light-Emitting Diodes

Abstract

Two-dimensional perovskites that could be regarded as natural organic–inorganic hybrid quantum wells (HQWs) are promising for light-emitting diode (LED) applications. High photoluminescence quantum efficiencies (approaching 80%) and extremely narrow emission bandwidth (less than 20 nm) have been demonstrated in their single crystals; however, a reliable electrically driven LED device has not been realized owing to inefficient charge injection and extremely poor stability. Furthermore, the use of toxic lead raises concerns. Here, we report Sn­(II)-based organic–perovskite HQWs employing molecularly tailored organic semiconducting barrier layers for efficient and stable LEDs. Utilizing femtosecond transient absorption spectroscopy, we demonstrate the energy transfer from organic barrier to inorganic perovskite emitter occurs faster than the intramolecular charge transfer in the organic layer. Consequently, this process allows efficient conversion of lower-energy emission associated with the organic layer into higher-energy emission from the perovskite layer. This greatly broadened the candidate pool for the organic layer. Incorporating a bulky small bandgap organic barrier in the HQW, charge transport is enhanced and ion migration is greatly suppressed. We demonstrate a HQW-LED device with pure red emission, a maximum luminance of 3466 cd m–2, a peak external quantum efficiency up to 3.33%, and an operational stability of over 150 h, which are significantly better than previously reported lead-free perovskite LEDs.

Enhancing Performance and Stability of Tin Halide Perovskite Light Emitting Diodes via Coordination Engineering of Lewis Acid–Base Adducts

“…[34,35] The incorporation of the GraHIL further improved the luminance properties of the device to achieve L max of 68.84 cd m −2 and EQE max of 0.361% (Figure 5d-f and Figure S10, Supporting Information). Compared to the performance of PeLED devices based on pristine PEA 2 SnI 4 reported in recent studies, [15,16,18,36,37] the L max and EQE max of the S4, Supporting Information). We believe that optimization of the device with compositional and additive engineering will enable further improvement of the performance.…”

“…Among other elements, Sn has been widely studied for substituting Pb due to their similar valence electron configurations. [15][16][17][18][19] However, because Sn lacks lanthanide shrinkage, Sn 2+ ions are easily oxidized to Sn 4+ ions to cause detrimental Sn vacancies and impurities in the perovskite films. [20][21][22] Thus, regardless of the stringency in fabrication environment controls, an inevitable oxidation of the precursors and films result in much inferior device performance of Sn perovskite-based PeLEDs.…”

Advances and Challenges in Two-Dimensional Organic–Inorganic Hybrid Perovskites Toward High-Performance Light-Emitting Diodes

“…Thus, the lead-free red PeLED with the longest half-life and the highest EQE (5%) was obtained [114]. Dou et al used 7-(thiophen-2-yl) benzothiadiazol-4-yl)-[2,2'bithiophen]-5-yl)ethylammonium iodide (BTmI) as the barrier layers to display a pure red Snbased PeLED with a luminance of 3466 cd m −2 and a working stability of more than 150 h [184]. (111)-oriented 2D perovskites have also been used as LEDs, but they all show unsatisfactory efficiency.…”

Two‐dimensional halide perovskite quantum‐well emitters: A critical review

“…Very recently, our group also reported tin‐based n = 1 hybrid quantum wells employing molecularly tailored organic semiconducting barrier layers. Introducing a bulky small bandgap organic barrier in the HQW, charge transport is enhanced and ion migration is greatly suppressed, which enables efficient and stable lead‐free perovskite LEDs 85 . We envision that this organic cation design strategy could be a new promising direction for the development of highly stable and efficient perovskite LEDs and lasers in the future.…”