an anode;

a cathode;

an organic layer between the anode and the cathode and comprising an emission layer; and

a first exciton quenching layer between the anode and the emission layer and in direct contact with the emission layer,

wherein the emission layer comprises a host and a dopant,

the first exciton quenching layer comprises a first quenching material, and

the host, the dopant, and the first quenching material satisfy Equations 1-1 and 1-2:

wherein, in Equations 1-1 and 1-2,

T1(Q1) indicates a lowest excited triplet energy level of the first quenching material,

T1(H) indicates a lowest excited triplet energy level of the host, and

T1(D) indicates a lowest excited triplet energy level of the dopant,

wherein the first quenching material is represented by Formula 3:

Formula 3

wherein, in Formula 3,

X₁ is N-(L₄)_a4-(Ar₁)_b1, O, or S,

A is a substituted or unsubstituted C₆-C₂₀ aromatic ring,

R₁ to R₄ are each independently a group represented by Formula 10, hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a substituted or unsubstituted C₁-C₆₀ alkyl group, a substituted or unsubstituted C₂-C₆₀ alkenyl group, a substituted or unsubstituted C₂-C₆₀ alkynyl group, a substituted or unsubstituted C₁-C₆₀ alkoxy group, a substituted or unsubstituted C₃-C₁₀ cycloalkyl group, a substituted or unsubstituted C₂-C₁₀ heterocycloalkyl group, a substituted or unsubstituted C₃-C₁₀ cycloalkenyl group, a substituted or unsubstituted C₂-C₁₀ heterocycloalkenyl group, a substituted or unsubstituted C₆-C₆₀ aryl group, a substituted or unsubstituted C₆-C₆₀ aryloxy group, a substituted or unsubstituted C₆-C₆₀ arylthio group, a substituted or unsubstituted C₁-C₆₀ heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —Si(Q₁)(Q₂)(Q₃), or —B(Q₁)(Q₂),

Formula 10

wherein, in Formulae 3 and 10,

L₁ to L₄, L₃₁ and L₃₂ are each independently a substituted or unsubstituted C₃-C₁₀ cycloalkylene group, a substituted or unsubstituted C₁-C₁₀ heterocycloalkylene group, a substituted or unsubstituted C₃-C₁₀ cycloalkenylene group, a substituted or unsubstituted C₁-C₁₀ heterocycloalkenylene group, a substituted or unsubstituted C₆-C₆₀ arylene group, a substituted or unsubstituted C₁-C₆₀ heteroarylene group, a substituted or unsubstituted divalent non-aromatic condensed polycyclic group, or a substituted or unsubstituted divalent non-aromatic condensed heteropolycyclic group,

a1 to a4 and a31 to a32 are each independently 0, 1, 2, or 3,

Ar₁, Ar₃₁ and Ar₃₂ are each independently a substituted or unsubstituted C₃-C₁₀ cycloalkyl group, a substituted or unsubstituted C₁-C₁₀ heterocycloalkyl group, a substituted or unsubstituted C₃-C₁₀ cycloalkenyl group, a substituted or unsubstituted C₁-C₁₀ heterocycloalkenyl group, a substituted or unsubstituted C₆-C₆₀ aryl group, a substituted or unsubstituted C₁-C₆₀ heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, or a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group,

b1, b31, and b32 are each independently 1, 2, 3, 4, or 5,

Ar₃₁ and Ar₃₂ are optionally bound to each other to form a saturated or unsaturated ring,

c1 is 1, 2, 3, or 4, c2 is 1, 2, or 3, and c3 and c4 are each independently 1, 2, 3, 4, or 5, and

when c1 is 2 or greater, two of R₁(s) are optionally bound to form a saturated or unsaturated ring, when c2 is 2 or greater, two of R₂(s) are optionally bound to form a saturated or unsaturated ring, when c3 is 2 or greater, two of R₃(s) are optionally bound to form a saturated or unsaturated ring, and when c4 is 2 or greater, two of R₄(s) are optionally bound to form a saturated or unsaturated ring, and

Q₁ to Q₃ are each independently hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C₁-C₆₀ alkyl group, a C₂-C₆₀ alkenyl group, a C₂-C₆₀ alkynyl group, a C₁-C₆₀ alkoxy group, a C₃-C₁₀ cycloalkyl group, a C₁-C₁₀ heterocycloalkyl group, a C₃-C₁₀ cycloalkenyl group, a C₁-C₁₀ heterocycloalkenyl group, a C₆-C₆₀ aryl group, a C₁-C₆₀ heteroaryl group, a monovalent non-aromatic condensed polycyclic group, or a monovalent non-aromatic condensed heteropolycyclic group.