Method of making a solar cell

A method of making a solar cell includes: preparing an active layer solution including p-type and n-type organic semiconductor materials, a solvent, and an additive, the additive containing 1, 8-iodooctane (DIO) and 1-chloronaphthalene (CN) that has a total volume not greater than 3 vol % based on a total volume of the solvent and the additive; preparing an assembly having a substrate, a first electrode layer, and a first transporting layer; coating the active layer solution on the first transporting layer to form a wet active layer; drying the wet active layer at a temperature not greater than 60° C.; and forming a second transporting layer and a second electrode layer on the active layer.