The efficiency of blue perovskite light-emitting diodes (PeLEDs) is lagging far behind their green and red counterparts. Here, we demonstrate high-efficiency sky-blue PeLEDs by employing pseudohalide thiocyanates, which are ammonium thiocyanate (NH₄SCN), methylammonium thiocyanate (MASCN), and guanidine thiocyanate (GASCN), as additives in a quasi-two-dimensional cesium lead halide perovskite emission layer. Although the thiocyanate incorporation can modify the formation energy to induce more n = 1 phases that are undesirable for light emission due to their strong electron–phonon coupling, the pseudohalide additive is able to passivate the nonradiative trap defects and stabilize the perovskite structure by filling the halide vacancy, coordinating to Pb with the Pb–S bond, and enhancing the bonding of the perovskite lattice. It is found that the passivation effect outperforms the electron–phonon coupling loss, yielding a higher photoluminescence quantum yield. As a result, the external quantum efficiencies of the sky-blue PeLEDs are improved from 5.75 to 11.93%. The thiocyanate-modulated devices also exhibit good spectral and operational stability. This work revealed the important roles of the pseudohalide thiocyanates in the improvement of sky-blue PeLEDs.

中文翻译：

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通过电子-声子耦合损耗和缺陷钝化之间的权衡实现高效天蓝色钙钛矿发光二极管

蓝色钙钛矿发光二极管 (PeLED) 的效率远远落后于绿色和红色对应物。_{在这里，我们通过使用拟卤化物硫氰酸盐（即硫氰酸铵 (NH 4} SCN)、甲基硫氰酸铵 (MASCN) 和硫氰酸胍 (GASCN)）作为准二维铯铅中的添加剂来展示高效天蓝色 PeLED卤化物钙钛矿发射层。虽然硫氰酸盐的掺入可以改变形成能以诱导更多的n= 1 相，由于其强电子 - 声子耦合，不适合发光，拟卤化物添加剂能够通过填充卤化物空位来钝化非辐射陷阱缺陷并稳定钙钛矿结构，与 Pb 配位 Pb-S 键，并增强钙钛矿晶格的键合。发现钝化效应优于电子 - 声子耦合损失，产生更高的光致发光量子产率。结果，天蓝色 PeLED 的外部量子效率从 5.75% 提高到 11.93%。硫氰酸盐调制的装置还表现出良好的光谱和操作稳定性。这项工作揭示了拟卤化物硫氰酸盐在改善天蓝色 PeLED 中的重要作用。