Carrier collection in optically resonant nanostructures for quantum dot solar cells

One of the most interesting - but often underappreciated - absorber materials for solar cells are PbS quantum dot (QD) layers. In principle, the tuneable bandgap, that derives from quantum confinement, together with strong absorption, which allows for thin and flexible layers, as well as the ease of fabrication in form of solution deposition, are each strong arguments for thin-film-QD absorber layer based solar cells. However, so far, those advantages have been met with notable disadvantages which have hindered a faster and more enthusiastic uptake of QD absorber layers in the scientific community. A major hindrance is the low diffusion length of charge carriers in the absorber, limiting the maximum possible absorber thickness, thus requiring an unsatisfying compromise between short-circuit current density (J SC ) and open-circuit voltage (V OC ). In this work, we lay out a path on how to address this issue, by introducing a 3-dimensionally structured p-n heterojunction ( Fig. 1 ) that can increase charge carrier generation, as well as improve extraction in comparison to flat cell geometries.