We study the radiative decay, or fluorescence, of excitons in organic solar cells as a function of its geometrical parameters. Contrary to their nonradiative counterpart, fluorescence losses strongly depend on the environment. By properly tuning the thicknesses of the buffer layers between the active regions of the cell and the electrodes, the exciton lifetime and, hence, the exciton diffusion length can be increased. The importance of this phenomenon depends on the radiative quantum efficiency, which is the fraction of the exciton decay that is intrinsically due to fluorescence. Besides this effect, interferences within the cell control the efficiency of sunlight injection into the active layers. The optimal cell design must rely on a consideration of these two aspects. By properly managing fluorescence losses, one can significantly improve the cell performance. To demonstrate this fact, we use realistic material parameters inspired from literature data and obtain an increase of power-conversion efficiency from 11.3% to 12.7%. Conversely, not to take into account the strong dependence of fluorescence on the environment may lead to a suboptimal cell design and a degradation of cell performance. The presence of radiative losses, however small, significantly changes the optimal set of thicknesses. We illustrate the latter situation with experimental material data.

We present here the effect of the common Ag electrode thickness, h 3 , in both TRTC and ITO-tandem configurations and also the I sc as a function of the active layer thickness in both TRTC and ITO-single configurations for the nine cell presented in Table I.

We compare the performances of single cells, parallel and series homo-tandem solar cells by focusing on the effect of a central ultra thin metal film acting as an interconnecting layer in the series case or as an electrode in the parallel case. Cells with this metal film are found to outperform classic solar cells thanks to better interference management. Moreover, we find that photonic optimization from an absorption point of view can be accompanied by a reduction of the total amount of active material. We show that the best types of cell strongly depends on the maximum allowed active material thickness to ensure good carrier collection. We also compare ITO and a recently devised ITO-free alternative, the Two-Resonance Tapping Cavity, as transparent electrode and we show how this choice influences

We revisit the argument that link the efficiency of a solar cell to its reverse operation as a LED, in the case where the material is organic. In organic cells, exciton transport is an intermediate process between sunlight absorption and the generation of electric current. We show that quenching exciton radiation can be beneficial to cell efficiency, without contradicting the general rule prevailing for semiconductor cells. Our treatment allows us to discuss both bulk heterojunction and planar junctions.

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