combination occurs and to determine, for example, the thickness of the recombination zone and the current density. The methods and models described herein can be used advantageously in complex stack arrangements and devices to predict quickly and precisely properties such as the efficiency of the charge recombination, emissions and current densities. For example, layer thicknesses of the ETL, EML and HTL can be automatically determined to maximize light output by simulating as described above for various layer thicknesses and picking the design that works best. More generally, one can consider a partial input specification of composition and geometry of the device to be designed. Simulations as above can be automatically done for several cases, where each case is defined by selecting values as needed for device parameters to complete the input specification. Typically a simulation space is defined by selecting the parameters to be varied in the design process, and the corresponding ranges over which they can vary. E.g., EML thickness in a range of 20 nm to 100 nm could be a first such parameter, ETL thickness in a range from 5 nm to 30 nm could be a second such parameter and HTL thickness in a range from 5 nm to 30 nm could be a third such parameter. The cases are determined by systematically exploring this simulation space and providing the resulting optimized device configuration as an output. I this example, the result would be optimized ETL, EML, LITL thicknesses as determined by simulations as described above. The optimization to be used depends on the kind of device being designed. E.g., for a light emitting diode, light emission at the device’sintended operating point could be maximized. For a solar cell, parameters such as open circuit voltage, short circuit current and/or fill factor can be maximized. Figs. 1A-B show exemplary simulation times for several simulation approaches vs. applied voltage. Fig. 2 shows dependence of part of the recombination rate prefactor on various parameters. Fig. 3A show a device configuration as used in simulations. Fig. 3B shows simulation results for the configuration of Fig. 3A. BRIEF DESCRIPTION OF THE DRAWINGS