The promise for next generation light-emitting device (LED) technologies is a major driver for research on nanocrystal quantum dots (QDs). The low efficiencies of current QD-LEDs are often attributed to luminescence quenching of charged QDs through Auger-processes. Although new QD chemistries successfully suppress Auger recombination, high performance QD-LEDs with these materials have yet to be demonstrated. Here, QD-LED performance is shown to be significantly limited by the electric field. Experimental field-dependent photoluminescence decay studies and tight-binding simulations are used to show that independent of charging, the electric field can strongly quench the luminescence of QD solids by reducing the electron and hole wavefunction overlap, thereby lowering the radiative recombination rate. Quantifying this effect for a series of CdSe/CdS QD solids reveals a strong dependence on the QD band structure, which enables the outline of clear design strategies for QD materials and device architectures to improve QD-LED performance.