Developing light-emitting diodes (LEDs) with the merits of low driving and high brightness has always been attractive. Considering the carrier dynamic process under electroexcitation, the built-in potential (V_bi) represents the moment that the photons start to be produced in a LED. However, it has not been carefully studied and discussed. Here, we observed that by employing an interface regulation strategy to enhance hole concentration, the V_bi of quantum dot LEDs (QLEDs) can be reduced. Combined with the characterization methods of Mott–Schottky (MS) and scanning Kelvin probe microscopy (SKPM), the key indicator of V_bi on driving voltage for QLEDs is confirmed. Profiting from the reduction of V_bi, a record-breaking ultra-low turn-on voltage of 2.2 V (@1 cd/m²) is achieved in a blue QLED. The blue QLED shows an advantage of high brightness under low driving voltages, i.e., 1000 cd/m²@3.10 V and 5000 cd/m²@3.88 V. This work proposes a reference strategy to predict and analyze the driving voltage issue, which is beneficial to facilitating the development of low-driving QLEDs in the future.