Fig. 4
From: Understanding how excess lead iodide precursor improves halide perovskite solar cell performance

FE-SEM and HR-TEM cross-sectional images (a control-HaP, d w/-PbI2-HaP) and HR-TEM cross-sectional images (b control-HaP, e w/-PbI2-HaP). HR-TEM images c and f show magnifications of images b and e respectively, of the HaP layer area. Red arrows indicate unreacted HaP with PbI2 residues (or clusters) and blue arrows in rectangles (dashed or solid) correspond to the direction of lattice planes