In this work, we have measured the absolute PLQY of TPE-BBT in THF solution to be 4.17% using an integrating sphere instrument. The high PLQY and suitable absorption and emission wavelength suggest that TPE-BBT could be a reliable PLQY standard for NIR-II materials. TPE-BBT solution exhibits negligible concentration-dependent PLQY changes within the absorbance range of 0.01 to 0.1 at 808 nm at room temperature, and no aggregation was observed within this range. Using the PLQY value of the TPE-BBT solution as a standard, we successfully measured and calibrated the PLQY for two commercially available NIR-II PLQY standards, namely IR-26 (PLQY = 0.0301% in DCE) and IR-1061 (PLQY = 0.193% in DCM). The calibrated value of IR-26 enables the relative PLQY measurements to show only slight deviations from the absolute value, accurately reflecting the PLQY of the samples. Our results confirm that the THF solution of TPE-BBT can serve as a reliable PLQY standard for NIR-II fluorophores.