Can Perovskite Light Emitting Diodes Achieve Maximum Efficiency at Sub-Band-Gap Voltages?

Ultra-low-voltage operation of perovskite light emitting diodes (PeLEDs) was demonstrated in recent years. However, the light output at such conditions from PeLEDs is usually very low, and the maximum external quantum efficiency (EQE) and power conversion efficiency (PCE) are typically achieved at large biases with significant power consumption. Here, we explore the possibility of achieving maxima in EQE and PCE at sub-band-gap voltages for PeLEDs. Our analysis consistently interprets otherwise scattered experimental data from the literature, identifies the limits for low-voltage operation, and elucidates optimization routes for sub-band gap high-radiance operation of PeLEDs.