Simulated Annealing Electro-Photonic Optimization Of Organic Solar Cells

Micro-patterned organic solar cells can exhibit enhanced light absorption properties due to a photonic crystal effect [Tumbleston et al., Appl. Phys. Lett. 94, 043305 (2009)]. Here, a three-dimensional model of light absorption and charge carrier transport in micro-patterned materials is presented and applied to the design of organic bulk heterojunction (BHJ) solar cells. Rigorous coupled wave analysis is used to simulate the multiple scattering and absorption of light in a layered solar cell device. The non-linearly coupled steady-state electric field and charge transport equations are solved iteratively by a sequence of linear partial differential equations (PDEs). Each linear PDE is discretized by an exponential upwind finite difference scheme, and the preconditioned conjugate gradient method is applied to the resulting algebraic system. The electro-photonic solver is coupled with the simulated annealing optimization algorithm to investigate the effect of micro-patterning upon performance of BHJ solar cells. Starting from the baseline configuration of a cell formed from flat layers of optimal thickness, the optimization algorithm leads to improvements of up to 15% in energy conversion efficiency by patterning both the front and back electrodes with a periodic ridge shape, with conformally coated layers in-between. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4748314]