Lea Nienhaus – Florida State University
Title: Stressing Halide Perovskites: Nanoscale Investigation of the Properties of Perovskite Thin Films

Abstract: Solution-processed perovskite thin films consist of small grains with a size of 20 – 2000 nm connected by grain boundaries. As a result, there is a vast inhomogeneity in the optical and electronic properties of the different grains/GBs within one film, which can reduce the achievable energy output. In addition, facile ion movement under external stimuli (light or electric fields) adds additional complexity to the system. However, solvents can also be used to change the surface doping, which can have immense impact on energy or charge transfer at the perovskite surface.

To gain insight into the optoelectronic and structural response of the perovskite thin film to these external stressors present under operating conditions, we utilize a combination of scanning tunneling microscopy (STM) and optical spectroscopy. Furthermore, single molecule absorption STM (SMA-STM) can probe the local inhomogeneity of the surface properties of the perovskite thin film under illumination by locally mapping the additional photogenerated tunneling current. To understand whether the local changes are caused by optoelectronic changes under illumination or structural changes, we utilize synchrotron X-ray STM (SX-STM). Pump-probe wide-angle X-ray scattering indicates the presence of lattice deformations under optical illumination, highlighting that the photocarriers distort the lattice, and thus, can change the underlying density of states as observed by SMA-STM.

Speaker bio: Lea Nienhaus obtained her PhD from UIUC in 2015. Following her postdoc at MIT, she transitioned to FSU in 2018. Her interests are geared towards pushing the boundaries of optical spectroscopy. Outside of lab, you can find her playing with her cats, biking, swimming or cooking. Additionaly, she enjoys shining UV lights on household objects.