Quantum confinement in the spectral response of n-doped germanium quantum dots embedded in an amorphous Si layer for quantum dot-based solar cells

Quantum dot solar cells are based on the concept of harvesting different parts of the solar light spectrum with a single, cheap semiconductor by simply changing the size of the nanoparticles. Of the many compositions explored, germanium is one of the most interesting as it has the major advantage of a large Bohr radius, which allows for the fabrication of larger particles. Moreover, germaniums possess very high optical absorption, and a small band gap give it free parameters to optimize the quantum dot solar cell. In a previous work, the germanium quantum dots were used in a Gratzel type solar cell containing an electrolyte, which is not desirable for applications. In this work instead, the n-doped germanium quantum dots were combined with a p-doped a-Si layer, making it the first all solid-state solar cell made from nanoparticles from a gas aggregation nanoparticle source. Remarkably, the effect of quantum confinement in both the germanium quantum dot assembled layer and a-Si was observed by peaks in the spectral response experiments. This work forms an important step toward realizing a germanium quantum dot based solar cell and studying quantum dot based solids.