Solar cell with extremely thin absorber on highly structured substrate

We report the optical, structural and photovoltaic properties of an extremely-thin-absorber (eta) solar cell on highly porous TiO2 substrates. Nano-crystalline absorber layers with a local thickness of only 150 nm have been prepared. This small absorber thickness allows good carrier collection even for absorber material with poor transport properties. The morphology of the highly structured TiO2 substrate produces strong internal light scattering, resulting in an enhancement of the optical path length by a factor 5. With 150 nm thick CdTe absorber layers, the eta solar cells produce an open-circuit voltage of 0.67 V and a short-circuit current of 8.9 mA cm−2 for 100 mW cm−2 illumination. Alloying the CdTe with Hg improves the short-circuit current to 15 mA cm−2.