a cation represented by Formula 3 and

a counter anion,

wherein, in Formula 3,

R₁′, R₂′, R₃′, R₄′, and R₅′ are each independently a hydrogen atom, a halogen atom, a C1-C20 alkyl group, or a C1-C20 haloalkyl group,

R₆′, R₇′, R₈′, R₉′, R₁₀′, R₁₁′, R₁₂′, R₁₃′, R₁₄′, and R₁₅′ are each independently a hydrogen atom, a halogen atom, a hydroxy group, a cyano group, a substituted or unsubstituted C1-C30 alkyl group, a substituted or unsubstituted C1-C30 alkoxy group, a substituted or unsubstituted C3-C30 cycloalkyl group, a substituted or unsubstituted C6-C30 aryl group, or a substituted or unsubstituted C6-C30 heteroaryl group, or R₁₀′ and R₁₁′ join to form a ring system, and

at least two of R₆′, R₇′, R₈′, R₉′, R₁₂′, R₁₃′, R₁₄′, and R₁₅′ are iodine atoms.