Optical modeling and optimization of multilayer organic photovoltaic cells

We show that the spectral position of the maxima in the exciton generation rate G in a photovoltaic cell, taking into account the spectral energy distribution in the AM1,5G solar spectrum, is determined by the absorption bands of its donor and acceptor materials. It varies slightly as the thicknesses of the layers in the cell change. Interference of light affects only the magnitude of these maxima. For a cell based on a CuPc (copper phthalocyanine)-C60 (fullerene) heterojunction, the G maxima are located at 640 nm, 720 nm (absorption in CuPc) and close to 495 nm (absorption in C60). The photovoltaic cell can be optimized using the ratio of the magnitudes of these maxima and their variations as layer thicknesses are varied and the exciton diffusion length is taken into account.(authors)