Modeling optical effects and thickness dependent current in polymer bulk-heterojunction solar cells

Device characteristics of polymer based bulk-heterojunction photovoltaic cells incorporating poly[2-methoxy-5-($2^{\prime }$ -ethyl-hexyloxy)-1,4-phenylene vinylene] and methanofullerene ([6,6]-phenyl ${\mathrm{C}}_{61}$ -butyric acid methyl ester) as the active materials are examined as a function of active layer thickness. The dependence of short circuit current on optical effects and its oscillatory variation on the polymer layer thickness is explained by solving the short circuit current using the drift-diffusion equations, where the light intensity calculated from the optical transfer matrix theory is used as the input for optical carrier generation. Furthermore, the effects of polymer layer thickness on other device operation parameters such as open-circuit voltage, fill factor, and series resistivity are measured. Considering the variation of above mentioned parameters, an optimized power conversion efficiency as high as 1.8% (under simulated air mass 1.5 global conditions) was achieved for a device with a polymer layer thickness of $55\mathrm{nm}$ .