In Figure , we summarize these results by plotting the percent improvement in the φ ET2 × (1-φ BT ) term and the φ ET1 term for different PbS concentrations. The contributions from triplet extraction decrease with an increase in PbS thickness. Meanwhile, the improvements in the φ ET2 × (1-φ BT ) term increase sharply with PbS concentration. There is a nearly (2500 ± 500)% improvement in the φ ET2 × (1-φ BT ) term while there is a (4 ± 2)% improvement in the φ ET1 term for 50 mg/mL PbS films. This suggests that the issues of back energy transfer to PbS QDs are far more severe for thicker PbS films, resulting in larger improvements in EQE upon the introduction of TCA as a blocker layer. By successfully addressing the bottleneck of back energy transfer while maintaining forward energy transfer, we are able to achieve manyfold higher IQEs for strongly absorbing UC films. Anti-Counterfeiting Demonstration: