those calculated from the 3D-KMC simulations. The site-resolved recombination rates as obtained from the 3D-ME and 3D-KMC simulations are excellently correlated. However, for sites at which the recombination rates from 3D-KMC simulations is relatively large, the 3D-ME simulations overestimate the recombination rate by a factor 2 3. As the recombination rate is largest in thin zones near the EML/HTL and EML/ETL interfaces, we view this overestimation as a consequence of neglecting the carrier concentration gradients in these regions on a 2—5 nm scale. The recombination rate on sites at which in the 3D-KMC simulation recombinations seldomly take place is underestimated by the 3D-ME simulations. To better visualize the site-resolved results, we show in Fig. 6 cross sections of the device in Fig. 3A and plot the 2D contour profile of carrier concentration and recombination rate. The “hotspots”correspond to sites with high carrier concentra tions or recombination rates. Consistent with Fig. 5, while the site-resolved carrier concentration in KMC is well-reproduced by ME, the site-resolved recombination rate shows some differences. The results of Fig. 6 are from the layer at x = 21 nm (the layer in the EML that is adjacent to the EML/HTL interface). The left panels are 3D-KMC results and the right panels are 3D-ME results. A color version of Fig. 6 can be found in Liu et ah, (“Three-DimensionalModeling of Bipolar Charge-Carrier Transport and Recombination in Disordered Organic Semiconductor Devices at Low Voltages” , Phys. Rev. Applied, vol. 10, 2018, 054007). In Eq. (4), recombination has been described as a “nearest-neighbor” process, instead of a “local” process with a rate at site i proportional to c/c$^{fi}$. I order to compare the effect of these two alternative approaches, we compare the results of 3D—ME and 3D—KMC simulations for a 100 nm single-layer device with a symmetric energy level structure as shown in the inset of Fig. 7 for the case of positive, negative and vanishing correlation between the HOMO and LUMO energies (see the top part of Fig. 7). As was shown in the literature, both types of disorder can be found in actual materials: electrostatic fields give rise to a positive correlation and configurational disorder can give rise to negative correlation. A robust model should be valid for all cases. Fig. 7 shows that KMC simulations reveal that the type of correlation has no significant C . “LOCAL” VERSUS “NEAREST-NEIGHBOR” DESCRIPTIONS OF R E COMBINATION