Although there is an improvement in Dexter energy transfer efficiency from QDs upon introduction of the TCA layer, this improvement accounts for only a small fraction of the improvement in EQE. Using Equation , we calculated the percent improvement in the remaining φET2 x (1 -φBT) term which includes the improvements resulting from back transfer alleviation (see Figure ). For this calculation, we used our measured values for EQE, φET1, and DBP/rubrene PLQY (~38%), and we assumed the φTTA to be 31% based on measurements from Di et al. We note that there may be minor changes in φTTA upon introduction of TCA as an interlayer due to changes in rubrene crystallization. Under the assumption of minimal changes in φTTA, we found that there are massive improvements in the φET2 x (1 -φBT) term, especially at thicker PbS QD films (see Figure ). For all thicknesses of PbS films, we observe a significant increase in the φET2 x (1 -φBT) term upon the introduction of 3 mM TCA. With increasing PbS film thickness, the decline in φ ET2 × (1-φ BT ) is substantial for samples without TCA (orange bars), while the decline is significantly mitigated for 3 mM and 6 mM TCA samples (blue and yellow bars in Figure ). This is likely due to the spatial separation of the donor (rubrene/DBP) and acceptor (PbS QDs) in the FRET-based energy transfer using 3 mM (~10 nm thickness) and 6 mM TCA (~18 nm thickness).