Comparison between 1D and 2D optoelectronic simulation of organic solar cell

One of central challenge in organic solar cells (OSC) is the light coupling into the active layer of the solar cell in order to increase its efficiency [1]. Several solutions can be used to increase the light harvesting such as back contact gratings or metallic nanoparticles. For the complexity of the problem, new design techniques are necessary to develop and simulate high performance organic solar cells. The transfer matrix method [2], typically used to obtain the optical absorption in OSC, is not suitable to estimate the light harvesting in solar cell with grating configuration. 2D and 3D electromagnetic simulation is required for this scope [3]. Electromagnetic simulation gives information on the optical behavior of the solar cell but they must be coupled with driftdiffusion modeling in order to obtain also electrical characteristics of the cell. The final scope of this work is to perform a whole 3D simulation of organic solar cell with the possibility of studying any cell architecture and materials. As first step we started from a flat case in order to compare the transfer matrix formalism with the coupled electromagnetic and drift diffusion simulations in order to confirm the reliability of our method. We studied a flat organic solar cell with the following structure : Glass/ITO/PEDOT/P3HT:PCBM/Al. We compared the transfer matrix method with 2D electromagnetic simulation of flat and homogeneous organic solar cells and we report in figure 1a the generation rate within the active layer for different active layer thicknesses. As it is possible to see the two different methods led to the same results. The generation rate profile has been then imported into the Tibercad simulator for drift diffusion simulations. These simulations allowed us to extract the I-V characteristics of the organic solar cell. Drift diffusion calculations have been performed starting by the generation rate obtained both from transfer matrix method and electromagnetic simulations. In figure 1b the comparison between the obtained I-V characteristics of the OSC with 200 nm active layer thickness are reported. Also for the electrical characteristics the two different methods give approximately the same results, the difference in terms of power conversion efficiency is of only 0,1 %. The obtained results show that this method can be used to design, in a fast way, new architectures of organic solar cell considering also back contact grating or nanoparticles for plasmonic effects.