A method of forming optoelectronic conversion layer includes the following steps. A first substrate is provided, and an electrode layer is formed on the first substrate. A first metal precursor layer including one or plural of metal components is formed on the electrode layer. A second substrate is provided, and a nonmetal precursor layer including at least one nonmetal component is formed on the second substrate. The first substrate and the second substrate are then stacked so that the nonmetal precursor layer and the first metal precursor layer are in contact. A thermal treatment is performed to have the first metal precursor layer react with the nonmetal precursor layer for forming an optoelectronic conversion layer.