There is provided a photovoltaic device that comprises a photoactive region, the photoactive region comprising a perovskite material of general formula A1-xA′xBX3-yX′y, wherein A is a formamidinium cation (HC(NH)2)2+), A′ is a caesium cation (Cs+) B is at least one divalent inorganic cation, X is iodide and X is bromide, and x is greater than 0 and equal to or less than 0.4 and y is greater than 0 and less than or equal to 3. There is also provided a method of producing a photovoltaic device comprising a photoactive region comprising the perovskite material, and formulations for use in the formation of the perovskite material.