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 (CsPbI₃) is metastable and spontaneously converts to the non-perovskite structure at room temperature. Here, we demonstrate that what appears to be all-inorganic CsPbI₃ stabilized in its perovskite form using the purported intermediate known as hydrogen lead iodide (HPbI₃) is, in fact, the hybrid perovskite cesium dimethylammonium lead iodide (Cs_1−xDMA_xPbI₃, 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_0.7DMA_0.3PbI₃ 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 CsPbI₃ while the DMA cation is now revealed as an alternative A site cation.