Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195-1700, United States.
Department of Physics, University of Oxford , Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom.
ACS Nano. 2017 Nov 28;11(11):11488-11496. doi: 10.1021/acsnano.7b06242. Epub 2017 Nov 10.
We use correlated confocal and wide-field fluorescence microscopy to probe the interplay between local variations in charge carrier recombination and charge carrier transport in methylammonium lead triiodide perovskite thin films. We find that local photoluminescence variations present in confocal imaging are also observed in wide-field imaging, while intensity-dependent confocal measurements show that the heterogeneity in nonradiative losses observed at low excitation powers becomes less pronounced at higher excitation powers. Both confocal and wide-field images show that carriers undergo anisotropic diffusion due to differences in intergrain connectivity. These data are all qualitatively consistent with trap-dominated variations in local photoluminescence intensity and with grain boundaries that exhibit varying degrees of opacity to carrier transport. We use a two-dimensional kinetic model to simulate and compare confocal time-resolved photoluminescence decay traces with experimental data. The simulations further support the assignment of local variations in nonradiative recombination as the primary cause of photoluminescence heterogeneity in the films studied herein. These results point to surface passivation and intergrain connectivity as areas that could yield improvements in perovskite solar cells and optoelectronic device performance.
我们使用相关共焦和宽场荧光显微镜来探测甲脒碘化铅钙钛矿薄膜中载流子复合和载流子输运之间的局部变化的相互作用。我们发现共焦成像中存在的局部光致发光变化也在宽场成像中观察到，而依赖于强度的共焦测量表明，在低激发功率下观察到的非辐射损耗的不均匀性在更高的激发功率下变得不那么明显。共焦和宽场图像都表明，由于晶粒间连接的差异，载流子经历各向异性扩散。这些数据与局部光致发光强度的陷阱主导变化以及表现出对载流子输运不同程度不透明性的晶界定性一致。我们使用二维动力学模型来模拟和比较共焦时间分辨光致发光衰减迹线与实验数据。模拟进一步支持将非辐射复合的局部变化作为研究中薄膜光致发光各向异性的主要原因。这些结果表明表面钝化和晶粒间连接是提高钙钛矿太阳能电池和光电设备性能的领域。
