Department of Chemistry , University of Washington , Seattle , Washington 98195-1700 , United States.
Physical Sciences Division , Pacific Northwest National Laboratory , Richland , Washington 99352 , United States.
Nano Lett. 2019 Feb 6;19(3):1931-1937. doi: 10.1021/acs.nanolett.8b05104.
Colloidal halide perovskite nanocrystals of CsPbCl doped with Yb have demonstrated remarkably high sensitized photoluminescence quantum yields (PLQYs), approaching 200%, attributed to a picosecond quantum-cutting process in which one photon absorbed by the nanocrystal generates two photons emitted by the Yb dopants. This quantum-cutting process is thought to involve a charge-neutral defect cluster within the nanocrystal's internal volume. We demonstrate that Yb-doped CsPbCl nanocrystals can be converted postsynthetically to Yb-doped CsPb(ClBr ) nanocrystals without compromising the desired high PLQYs. Nanocrystal energy gaps can be tuned continuously from E ≈ 3.06 eV (405 nm) in CsPbCl down to E ≈ 2.53 eV (∼490 nm) in CsPb(ClBr) while retaining a constant PLQY above 100%. Reducing E further causes a rapid drop in PLQY, interpreted as reflecting an energy threshold for quantum cutting at approximately twice the energy of the YbF → F absorption threshold. These data demonstrate that very high quantum-cutting energy efficiencies can be achieved in Yb-doped CsPb(ClBr ) nanocrystals, offering the possibility to circumvent thermalization losses in conventional solar technologies. The presence of water during anion exchange is found to have a deleterious effect on the Yb PLQYs but does not affect the nanocrystal shapes or morphologies, or even reduce the excitonic PLQYs of analogous undoped CsPb(ClBr ) nanocrystals. These results provide valuable information relevant to the development and application of these unique materials for spectral-shifting solar energy conversion technologies.
掺镱的胶体卤化物钙钛矿纳米晶 CsPbCl 的敏化光致发光量子产率（PLQY）非常高，接近 200%，这归因于皮秒量子裁剪过程，其中纳米晶吸收的一个光子产生两个由 Yb 掺杂剂发射的光子。这种量子裁剪过程被认为涉及纳米晶内部体积中的电荷中性缺陷簇。我们证明，Yb 掺杂的 CsPbCl 纳米晶可以在不影响所需高 PLQY 的情况下，通过后合成方法转化为 Yb 掺杂的 CsPb(ClBr)纳米晶。纳米晶的能隙可以从 CsPbCl 的 E ≈ 3.06 eV（405nm）连续调谐到 CsPb(ClBr)的 E ≈ 2.53 eV（∼490nm），同时保持超过 100%的恒定 PLQY。进一步降低 E 会导致 PLQY 迅速下降，这被解释为反映了量子裁剪的能量阈值，约为 YbF→F 吸收阈值能量的两倍。这些数据表明，Yb 掺杂的 CsPb(ClBr)纳米晶可以实现非常高的量子裁剪能量效率，有可能避免传统太阳能技术中的热化损失。发现阴离子交换过程中存在水会对 Yb PLQY 产生有害影响，但不会影响纳米晶的形状或形态，甚至不会降低类似未掺杂 CsPb(ClBr)纳米晶的激子 PLQY。这些结果为这些独特材料在光谱移动太阳能转换技术中的开发和应用提供了有价值的信息。
