Bias, length, or coupling? What controls the quantum efficiency of molecular electroluminescence

Using currents to control light emission of individual molecules has multiple motivations, including OLED design and the developmentof display technologies, optical interconnects in nanoscale circuits, chemical reaction mapping and detection with molecular resolution,optoelectronic logic gates, or single photon sources for quantum control. Yet, experiments struggle to discern the specific roles ofintrinsic and extrinsic factors on the emitted power and the quantum efficiency. Among such factors, the applied potential, the electrodecoupling, and the molecular length are critical. Through carefully validated time-dependent quantum electrodynamics modeling, wedecipher how these parameters can be chosen to achieve an exponential enhancement in the electroluminescence efficiency of individualpolymers, with polyphenylene-vinylene as a case study. In particular, we show that the applied bias is the primary factor determiningemission power, while the quantum efficiency is mostly controlled by the polymer length.