Touching is believing: interrogating organometal halide perovskite solar cells at the nanoscale via scanning probe microscopy

Organometal halide perovskite solar cells based on CH3NH3PbI3 and related materials have emerged as the most exciting development in the next generation photovoltaic technologies, yet the microscopic phenomena involving photo-carriers, ionic defects, spontaneous polarization, and molecular vibration and rotation interacting with numerous grains, grain boundaries, and interfaces are still inadequately understood. In fact, there is still need for an effective method to interrogate the local photovoltaic properties of solar cells that can be directly traced to their microstructures on one hand and linked to their device performance on the other hand. In this perspective, we propose that scanning probe microscopy techniques have great potential to realize such promise at the nanoscale, and highlight some of recent progresses and challenges along this line of investigation toward local probing of photocurrent, work function, ionic motion, polarization switching, and chemical degradation. We also emphasize the importance of multi-modality imaging, in-operando scanning, big data analysis, and multidisciplinary collaboration for further study toward fully understanding this complex system and developing a viable commercial device.