The present invention provides a solid state heterojunction solar cell comprising a transparent conducting support layer (2,3), on which a nanostructured, surface-increasing scaffold structure is provided, wherein an organic-inorganic perovskite layer (4) is provided on said scaffold structure, and wherein a counter electrode and/or metal layer (5) is provided in electric contact with said perovskite layer (4). According to an embodiment, the solar cell lacks an electrolyte or any hole conducting material. The invention also relates to a solid state ' heterojunction and to a method of preparing the solar cell.