To probe the source of improvements in EQE and IQE, we performed time-resolved upconversion photoluminescence (TRUCPL) and UC threshold measurements. We performed these measurements on 5 mg/mL PbS films with and without 3 mM TCA. To probe the effect of increasing PbS film thicknesses, we also performed these measurements on 10, 25, and 50 mg/mL PbS films with 3 mM TCA. We note that the control devices (without TCA) for thicker PbS films lacked sufficient UC signal to perform TRUCPL and threshold measurements.