A method of modifying the structure of a perovskite film prepared on a substrate, wherein an organic or inorganic salt crown ether complex is applied on a free surface of the so-prepared perovskite film. A perovskite solar cell, wherein a perovskite layer of said perovskite solar cell contains an organic or inorganic salt presenting a graded concentration within said perovskite layer , the highest concentration of said organic or inorganic salt existing in vicinity of the perovskite layer surface distal to the substrate of said perovskite layer .