New architecture for accurate characterization of the behavior of individual sub-cells within a tandem organic solar cell

The great challenge to improve the performance of a tandem organic solar cell is how we can measure the true behavior of its individual sub-cells. In this work, we develop a new architecture of the tandem solar cell to directly and accurately measure I-V and quantum efficiency of the individual sub-cells by using a very thin, semi-transparent metal interlayer with different surface modification as anode and cathode. Separate measurements of reference cells are used in the conventional method to evaluate the contribution of every individual sub-cell in a tandem structure. The discrepancy between the summations of two individual sub-cells in a tandem device and the sum of conventional two reference cells is significant. This great discrepancy is mainly ascribed to the light trapping effect from the rough silver interlayer connection. This work demonstrates that direct measuring of individual sub-cells in a tandem structure is the only way to evaluate the true contribution of each sub-cell, thus having important impact on the study of fundamentals and on the improvement of tandem solar cells.