Thickness dependence of photovoltaic performance of additional spray coated solar cells

We report the photovoltaic performance of solar cells with various active layer thicknesses prepared through “additional spray coating” method, which includes the spraying of o-dichlorobenzene (viz. pristine solvent) after the conventional spray coating of a mixture of poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester as active layer solution.The thickness of the active layer for which maximal efficiency was achieved was found to be around 220 nm with highly efficient light harvesting and charge transfer due to the minimization of internal pinholes. Particularly, the short circuit current and fill factor did not decrease severely with the increment of the thickness of the active layer (even to as high as 737 nm). This is as opposed to the spin coated device, which performance gradually drops with increasing thickness. This trend may be ascribed to the formation of uneven pathway for charge carriers and more efficient light harvesting due to the interconnection of droplets formed by additional solvent spray coating.

► Thick solar cell organic active layers were prepared by spray coating.
► The optimum active layer thickness of our spray coated layers was around 220 nm.
► The performance for organic spray coating is independent of device thickness.
► Even at above 700 nm, the power conversion efficiency remains 85% of the best device.
► Moderate drops of efficiency come from uneven pathway for charge carriers.