Organic solar cells have great potential for upscaling due to roll-to-roll processing and a low energy
payback time, making them an attractive sustainable energy source for the future. Active layers coated
with water-dispersible Landfester particles enable greater control of the layer formation and easier access
to the printing industry, which has reduced the use of organic solvents since the 1980s. Through ptychographic
X-ray computed tomography (PXCT), we image quantitatively a roll-to-roll coated photovoltaic
tandem stack consisting of one bulk heterojunction active layer and one Landfester particle active layer.
We extract the layered morphology with structural and density information including the porosity present
in the various layers and the silver electrode with high resolution in 3D. The Landfester particle layer is
found to have an undesired morphology with negatively correlated top- and bottom interfaces, wide
thickness distribution and only partial surface coverage causing electric short circuits through the layer.
By top coating a polymer material onto the Landfester nanoparticles we eliminate the structural defects
of the layer such as porosity and roughness, and achieve the increased performance larger than 1 V expected
for a tandem cell. This study highlights that quantitative imaging of weakly scattering stacked layers of
organic materials has become feasible by PXCT, and that this information cannot be obtained by other
methods. In the present study, this technique specifically reveals the need to improve the coatability and
layer formation of Landfester nanoparticles, thus allowing improved solar cells to be produced.