Accurate characterization of triple-junction Polymer Solar Cells

Triple-junction device architectures represent a promising strategy to highly efficient organic solar cells. Accurate characterization of such devices is challenging, especially with respect to determining the external quantum efficiency (EQE) of the individual subcells. The specific light bias conditions that are commonly used to determine the EQE of a subcell of interest cause an excess of charge generation in the two other subcells. This results in the build-up of an electric field over the subcell of interest, which enhances current generation and leads to an overestimation of the EQE. A new protocol, involving optical modeling, is developed to correctly measure the EQE of triple-junction organic solar cells. Apart from correcting for the build-up electric field, the effect of light intensity is considered with the help of representative single-junction cells. The short-circuit current density (J_SC) determined from integration of the EQE with the AM1.5G solar spectrum differs by up to 10% between corrected and uncorrected protocols. The results are validated by comparing the EQE experimentally measured to the EQE calculated via optical-electronic modeling, obtaining an excellent agreement.