Crystal Synthesis and Optical Properties of Cesium Lead Halide Solar Cells

Lead halide perovskites have rapidly emerged as efficient light-harvesters for thin-film photovoltaics. Solar cells made with partially organic perovskites, such as methylammonium lead iodide, have surpassed 20% efficiency; but have been observed to degrade under high temperatures and after long-term light exposure. Additionally, the optical properties of perovskites are dependent on crystal structure, and therefore formation temperature. Fully-inorganic cesium lead halide (CsPbX₃) perovskite is stable at higher temperatures than organic perovskite, allowing for control of the crystal structure through formation temperature, and potentially improving longevity in an active solar cell. This study reports the properties of CsPbX₃ perovskites and photovoltaic cells; specifically CsPbBr₃, CsPbI₃, and mixed halide intermediates. Crystal structures obtained were determined to vary from orthorhombic/tetragonal to cubic. Performance was best for cells containing perovskite in the cubic phase and light harvesting was best for cells with high iodide content, consistent with theory.