Accounting for interference, scattering, and electrode absorption to make accurate internal quantum efficiency measurements in organic and other thin solar cells.

In solar cells, internal quantum effi ciency (IQE) is the ratio of the number of charge carriers extracted from the cell to the number of photons absorbed in the active layer. Because IQE measurements normalize the current generation effi ciency by the light absorption effi ciency, they separate electronic properties from optical properties and provide useful information about the electrical properties of cells that external quantum effi ciency measurements alone cannot. The magnitude of the IQE is inversely related to the amount of recombination that is occurring in the cell, while the spectral shape of the curve can provide information about the effi ciency of harvesting excitons in the cell or spatial dependence of charge recombination. [ 1 , 2 ] Effects like multiple exciton generation [ 3–5 ] and singlet exciton fi ssion [ 6 ] as well as bias-dependent photoconductivity [ 7 ] can lead to interesting spectral shapes and be detected by measuring IQEs greater than 100%. Despite its usefulness as a characterization tool, IQE is rarely reported. When IQE is reported, absorption is frequently not measured in actual devices; this can lead to errors since refl ective electrodes induce strong interference effects that substantially affect absorption. When absorption is measured in actual devices, parasitic absorptions are almost never taken into account. We hope that by demonstrating a straightforward method of measuring IQE, it will become a standard measurement and the community may benefi t from a better understanding of how the best performing cells work. Organic photovoltaics (OPVs) and other ultra-thin solar cells [ 8–11 ]