Neutron Science Section, Japan Proton Accelerator Research Complex, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan.
Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Institute for Advanced Energy Materials, School of Materials Science and Engineering, Shaanxi Normal University, Xi'an 710119, China.
Nat Commun. 2017 Jun 30;8:16086. doi: 10.1038/ncomms16086.
Perovskite CHNHPbI exhibits outstanding photovoltaic performances, but the understanding of the atomic motions remains inadequate even though they take a fundamental role in transport properties. Here, we present a complete atomic dynamic picture consisting of molecular jumping rotational modes and phonons, which is established by carrying out high-resolution time-of-flight quasi-elastic and inelastic neutron scattering measurements in a wide energy window ranging from 0.0036 to 54 meV on a large single crystal sample, respectively. The ultrafast orientational disorder of molecular dipoles, activated at ∼165 K, acts as an additional scattering source for optical phonons as well as for charge carriers. It is revealed that acoustic phonons dominate the thermal transport, rather than optical phonons due to sub-picosecond lifetimes. These microscopic insights provide a solid standing point, on which perovskite solar cells can be understood more accurately and their performances are perhaps further optimized.
钙钛矿 CHNHPbI 表现出了卓越的光伏性能，但即使它们在输运性质中起着基本作用，对原子运动的理解仍不够充分。在这里，我们通过在大单晶样品上进行宽能量范围（0.0036 至 54meV）的高分辨率飞行时间准弹性和非弹性中子散射测量，分别展示了由分子跳跃旋转模式和声子组成的完整原子动态图像。在约 165K 时被激活的分子偶极子的超快各向异性无序，充当了光学声子以及载流子的额外散射源。研究结果表明，由于亚皮秒的寿命，声子主导热输运，而不是光学声子。这些微观见解提供了一个坚实的立足点，在此基础上可以更准确地理解钙钛矿太阳能电池，并进一步优化其性能。
