The role of masking and aperture size for accurate measurement of performance parameters of DSSCs

Abstract

DSSC efficiency is often reported with very little or no consideration of the cell area for which they are reported. Area masking of cells is almost always used for the measurement of cell performance parameters (Jsc, Voc, and FF). Although edge masking is required to exclude edge effects, a variety of masking including masking a major portion of the cells are frequently used to boost the apparent efficiency of the cell. In this work, it will be shown that the reported efficiency of a cell is strongly dependent on the exposed area. Two different kinds of cells have been considered in this work to elucidate the area effect: first is a large active area cell whose performance metrics are obtained by masking various fraction of the active area. Second, cells were fabricated with active areas ranging from small to large. A comparison of these two kinds of cells demonstrates that the cells with smaller areas show area-dependent performance parameters. A cell with a 4 mm² exposed area will show a higher efficiency of 10.47 % while the efficiency will drop to ∼ 3 % as the area increases to 60 mm² or higher. Such area dependence can be avoided if the cell area/exposed area selected is 60 mm² or above. The reason for the area dependence has been identified to be due to the presence of trap states and not due to scattering which is sometimes used in the literature to explain the area dependence.