Myths and reality of HPbI3 in halide perovskite solar cells

All-inorganic perovskites have a special place in halide perovskite family because of their potential for better stability. However, the representative cesium lead iodide (CsPbI 3 ) is metastable and spontaneously converts to the non-perovskite structure at room temperature. Here, we demonstrate that what appears to be all-inorganic CsPbI 3 stabilized in its perovskite form using the purported intermediate known as hydrogen lead iodide (HPbI 3 ) is, in fact, the hybrid perovskite cesium dimethylammonium lead iodide (Cs 1− x DMA x PbI 3 , x = 0.2 to 0.5). Thus, many of the reported all-inorganic perovskites are actually still hybrid organic-inorganic perovskites, as strongly evidenced by a wide battery of experimental techniques presented here. Solar cells based on the representative composition Cs 0.7 DMA 0.3 PbI 3 can achieve an average power conversion efficiency of 9.27 ± 1.28% (max 12.62%). These results provide an alternative angle to look at previous results pertaining all-inorganic CsPbI 3 while the DMA cation is now revealed as an alternative A site cation. Hydriodic acid or hydrogen lead iodide is widely used to stabilize all-inorganic perovskite cesium lead iodide to make high performing solar cells. Here Ke et al. reveal the real composition of the perovskites, where dimethylammonium partially take place of cesium cation at the A-site.