The critical role of grain boundaries for (CH(NH2)2PbI3)0.85(CH3NH3PbBr3)0.15 perovskite solar cells studied by Kelvin probe force microscopy under bias voltage and illumination is reported. Ion migration is enhanced at the grain boundaries. Under illumination, the light‐induced potential causes ion migration leading to a rearranged ion distribution. Such a distribution favors photogenerated charge‐carrier collection at the grain boundaries.

Beneficial effects are demonstrated by PbI2 incorporated into perovskite materials as a light absorber in solar cells. The PbI2 distributed into the perovskite layers leads to reduced hysteresis and ionic migration, and enables the fabrication of remarkably improved solar cells with a certified power conversion efficiency of 19.75% under air‐mass 1.5 global (AM 1.5G) illumination of 100 mW cm−2 intensity.

Although perovskite solar cells have produced remarkable energy conversion efficiencies, they cannot become commercially viable without improvements in durability. We used gas chromatography–mass spectrometry (GC-MS) to reveal signature volatile products of the decomposition of organic hybrid perovskites under thermal stress. In addition, we were able to use GC-MS to confirm that a low-cost polymer/glass stack encapsulation is effective in suppressing such outgassing. Using such an encapsulation scheme, we produced multi-cation, multi-halide perovskite solar cells containing methylammonium that exceed the requirements of the International Electrotechnical Commission 61215:2016 standard by surviving more than 1800 hours of the Damp Heat test and 75 cycles of the Humidity Freeze test.