Brown Alasdair A M, Hooper Thomas J N, Veldhuis Sjoerd A, Chin Xin Yu, Bruno Annalisa, Vashishtha Parth, Tey Ju Nie, Jiang Liudi, Damodaran Bahulayan, Pu Suan Hui, Mhaisalkar Subodh G, Mathews Nripan
School of Engineering, Faculty of Engineering and Physical Sciences, University of Southampton, Southampton SO17 1BJ, UK.
Energy Research Institute at NTU (ERI@N), Research Techno Plaza, X-Frontier Block Level 5, 50 Nanyang Drive, Singapore 637553, Republic of Singapore.
Nanoscale. 2019 Jul 7;11(25):12370-12380. doi: 10.1039/c9nr02566a. Epub 2019 Jun 19.
We report the self-assembly of an extensive inter-ligand hydrogen-bonding network of octylphosphonates on the surface of cesium lead bromide nanocrystals (CsPbBr NCs). The post-synthetic addition of octylphosphonic acid to oleic acid/oleylamine-capped CsPbBr NCs promoted the attachment of octylphosphonate to the NC surface, while the remaining oleylammonium ligands maintained the high dispersability of the NCs in non-polar solvent. Through powerful 2D solid-state P-H NMR, we demonstrated that an ethyl acetate/acetonitrile purification regime was crucial for initiating the self-assembly of extensive octylphosphonate chains. Octylphosphonate ligands were found to preferentially bind in a monodentate mode through P-O, leaving polar P[double bond, length as m-dash]O and P-OH groups free to form inter-ligand hydrogen bonds. The octylphosphonate ligand network strongly passivated the nanocrystal surface, yielding a fully-purified CsPbBr NC ink with PLQY of 62%, over 3 times higher than untreated NCs. We translated this to LED devices, achieving maximum external quantum efficiency and luminance of 7.74% and 1022 cd m with OPA treatment, as opposed to 3.59% and 229 cd m for untreated CsPbBr NCs. This represents one of the highest efficiency LEDs obtained for all-inorganic CsPbBr NCs, accomplished through simple, effective passivation and purification processes. The robust binding of octylphosphonates to the perovskite lattice, and specifically their ability to interlink through hydrogen bonding, offers a promising passivation approach which could potentially be beneficial across a breadth of halide perovskite optoelectronic applications.
我们报道了溴化铯铅纳米晶体（CsPbBr NCs）表面上广泛的辛基膦酸酯配体间氢键网络的自组装。在油酸/油胺封端的CsPbBr NCs上后合成添加辛基膦酸促进了辛基膦酸酯附着到NC表面，而剩余的油胺配体保持了NCs在非极性溶剂中的高分散性。通过强大的二维固态P-H NMR，我们证明乙酸乙酯/乙腈纯化方案对于引发广泛的辛基膦酸酯链的自组装至关重要。发现辛基膦酸酯配体通过P-O以单齿模式优先结合，使极性P=O和P-OH基团自由形成配体间氢键。辛基膦酸酯配体网络强烈钝化了纳米晶体表面，产生了PLQY为62%的完全纯化的CsPbBr NC墨水，比未处理的NCs高3倍以上。我们将此应用于LED器件，经OPA处理后实现的最大外量子效率和亮度分别为7.74%和1022 cd/m²，而未处理的CsPbBr NCs分别为3.59%和229 cd/m²。这代表了通过简单、有效的钝化和纯化过程获得的全无机CsPbBr NCs中效率最高的LED之一。辛基膦酸酯与钙钛矿晶格的牢固结合，特别是它们通过氢键相互连接的能力，提供了一种有前途的钝化方法，可能对广泛的卤化物钙钛矿光电子应用有益。
