A metallic salt comprising: at least one anion having a heterocyclic aromatic structure represented by one of Formulae 1 to 3; and a metallic cation: wherein, in Formulae 1 to 3, each X is independently N, P, or As, one of A 1 and A 2 is an electron-donating group, and the other one is an electron-withdrawing group, ring Ar 1 and ring Ar 2 are each independently an aromatic group selected from a substituted or unsubstituted C6 to C24 arylene group and a substituted or unsubstituted C4 to C24 heteroarylene group, wherein the aromatic group comprises a single aromatic ring, two or more aromatic rings which are fused together, or two or more aromatic rings which are connected covalently via a single bond, -O-, -S-, -C(=O)-, -S(=O) 2 -, -Si(R a)(R b)- wherein R a and R b are each independently a C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkylene group, or -C(=O)-NH-, and wherein Ar 1 and Ar 2 are each independently unsubstituted or substituted with at least one of an electron-donating group and an electron-withdrawing group, L is a linker group, and is a single bond, -O-, -S-, -C(=O)-, -S(=O) 2 -, -Si(R a)(R b)- wherein R a and R b are each independently a C1 to C10 alkyl group, -C(=O)-NH-, a substituted or unsubstituted C1-C12 alkylene group, a substituted or unsubstituted C2-C12 alkenylene group, a substituted or unsubstituted C2-C12 alkynylene group, a substituted or unsubstituted C6-C12 arylene group, or a substituted or unsubstituted C4-C12 heteroarylene group, wherein the linker group is unsubstituted or substituted with at least one of an electron-donating group and an electron-withdrawing group, and wherein the linker group is non-condensed or condensed with at least one of Ar 1 and Ar 2, m is an integer from 1 to 5, and n is an integer from 1 to 5, wherein the electron-donating group comprises at least one selected from -C n H 2n+1, -OC n H 2n+1, -NH 2, -NH(C n H 2n+1), -N(C n H 2n+1) 2, -OH, -NH(COC n H 2n+1), -N(COC n H 2n+1) 2, -OCOC n H 2n+1, -CH 2 (C n H 2n+1), -CH(C n H 2n+1) 2, -C(C n H 2n+1) 3, -SC n H 2n+1, -N(CH 2 CH 2) 2 O, -P 2, -P OH, a phenyl group, and a vinyl group, wherein n is an integer from 1 to 10. wherein, in Formulae 1 to 3, each X is independently N, P, or As, one of A 1 and A 2 is an electron-donating group, and the other one is an electron-withdrawing group, ring Ar 1 and ring Ar 2 are each independently an aromatic group selected from a substituted or unsubstituted C6 to C24 arylene group and a substituted or unsubstituted C4 to C24 heteroarylene group, wherein the aromatic group comprises a single aromatic ring, two or more aromatic rings which are fused together, or two or more aromatic rings which are connected covalently via a single bond, -O-, -S-, -C(=O)-, -S(=O) 2 -, -Si(R a)(R b)- wherein R a and R b are each independently a C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 alkylene group, or -C(=O)-NH-, and wherein Ar 1 and Ar 2 are each independently unsubstituted or substituted with at least one of an electron-donating group and an electron-withdrawing group, L is a linker group, and is a single bond, -O-, -S-, -C(=O)-, -S(=O) 2 -, -Si(R a)(R b)- wherein R a and R b are each independently a C1 to C10 alkyl group, -C(=O)-NH-, a substituted or unsubstituted C1-C12 alkylene group, a substituted or unsubstituted C2-C12 alkenylene group, a substituted or unsubstituted C2-C12 alkynylene group, a substituted or unsubstituted C6-C12 arylene group, or a substituted or unsubstituted C4-C12 heteroarylene group, wherein the linker group is unsubstituted or substituted with at least one of an electron-donating group and an electron-withdrawing group, and wherein the linker group is non-condensed or condensed with at least one of Ar 1 and Ar 2, m is an integer from 1 to 5, and n is an integer from 1 to 5, wherein the electron-donating group comprises at least one selected from -C n H 2n+1, -OC n H 2n+1, -NH 2, -NH(C n H 2n+1), -N(C n H 2n+1) 2, -OH, -NH(COC n H 2n+1), -N(COC n H 2n+1) 2, -OCOC n H 2n+1, -CH 2 (C n H 2n+1), -CH(C n H 2n+1) 2, -C(C n H 2n+1) 3, -SC n H 2n+1, -N(CH 2 CH 2) 2 O, -P 2, -P OH, a phenyl group, and a vinyl group, wherein n is an integer from 1 to 10.