The dynamic nature of hybrid perovskite crystal structure has enabled unusual optoelectronic properties. Subtle changes the structure can lead to dramatic changes in optical and electronic properties of perovskite based materials. In addition, external stimuli (light or electric field) significantly impacts the properties all the way from the molecular to the macroscale. While such a dynamic nature of the structure poses challenges using those material for device operation but also offer opportunity to discover new functionalities. Therefore, understanding the interplay between structure, light and electrical field using in-situ correlated measurements is critical not only for understanding optoelectronic transport processes, and but also for elucidating design principles for operation of perovskite based devices. In my talk, I will introduce our study on the correlation of perovskite structure and deformation in response to external stimulation (e.g. light and electrical field) to the device operation in perovskite based optoelectronic devices. Using correlated in-situ structure and transport measurements, I will focus on understanding these complex effects arising from the interaction between structure, light and field during perovskite cell operation in both 3D and 2D systems. Briefly, in a 3D perovskite system, we discover that continuous light illumination leads to a uniform lattice expansion in hybrid perovskite thin-films, which is critical for obtaining high-efficiency photovoltaic devices, boosting the power conversion efficiency from 18.5% to 20.5% in a planar perovskite solar cell. This is a direct consequence of lattice strain relaxation and increase in the crystallite size that dramatically suppresses the interface non-radiative recombination, resulting in enhanced photovoltage and photocurrent collection near low field. Similar studies on Ruddlesden-Popper 2D perovskites, a naturally formed quantum-well system, elucidates that the overall power conversion efficiency of solar cells is limited by the internal structure and built-in internal electrical field. Our results directly connect the electronic and optical processes with the structural properties and provides guidance on design principles perovskite based materials for high-efficiency and stable optoelectronic devices.