I–Br Ordered DMAPbI _{3– <i>x</i>} Br _<i>x</i> Crystal Intermediates Enabling High-Quality CsPbI _{3– <i>x</i>} Br _<i>x</i> Inorganic Perovskite Thin Films in Solar Cells

Cesium-based all-inorganic lead-halide perovskites CsPbX₃ (X = I, Br, Cl) have emerged as highly promising optoelectronic materials with a wide bandgap, which are commonly utilized in tandem solar cells. However, the I-Br hybrid CsPbI_3-<i>x</i>Br_<i>x</i> perovskites still face stability issues such as halide segregation-induced phase transition and decomposition under ultraviolet or high-temperature conditions. We synthesize a series of single crystals DMAPbI_3-<i>x</i>Br_<i>x</i> (<i>x</i> = 0.1, 0.15, 0.2, 0.3, 0.6), featuring an I-Br ordered distribution. By introducing the crystal intermediate into the perovskite precursor, we successfully obtained high-quality CsPbI_3-<i>x</i>Br_<i>x</i> thin films, exhibiting high stabilities and low trap state density. The formation kinetics of the high-quality perovskite thin films are in situ studied and the possible reaction mechanisms are proposed. Benefiting from this approach, the solar cells have an improved photoelectric conversion efficiency and significantly enhanced thermal stability. This method is proven to be feasible and innovatively offers a new strategy for the continuous development of mixed-halide perovskite solar cells.