Nanoscale photocurrent mapping in perovskite solar cells
Yohan Yoon, Dongheon Ha, Ik Jae Park, Paul M. Haney, Sangwook Lee, Nikolai B. Zhitenev
In this work, we study spatially-resolved generation of photocurrent of methylammonium lead iodide (CH3NH3PbI3) perovskite solar cells to reveal the microscopic effects of annealing temperature and degradation under light exposure. Correlating a novel nanoscale near-field scanning photocurrent microscopy (NSPM) technique with X-ray diffraction and electron microscopy data, we found that the segregation of lead iodide (PbI2) driven either by a temperature treatment or by extended light exposure can impact the photocurrent at the grain. In samples annealed at moderate temperature (100 °C), a small amount of expelled PbI2 passivates the grain boundaries and improves photocurrent generation. Larger annealing temperature causes further segregation of PbI2 at grain boundaries, decreasing the photocurrent. Extended light illumination drives further material segregation, decreasing photocurrent both at grain boundaries and grain interiors.