Hot charge carriers in tin-based perovskite solar cells to exceed the Shockley-Queisser limit

• Applicant: Dr. Simon Kahmann
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2018 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 408012143

Generated charge carriers in solar cells lose a considerable portion of their energy as heat due to thermalisation. This loss process commonly limits the maximum achievable power conversion efficiency of solar cells to approximately 33%. In this project, I shall investigate a material system – tin perovskite – in which charge carriers cool down slowly enough to enable a successful harvesting of the additional energy. The successful implementation would double the theoretically achievable power conversion efficiency to 66%.My focus first lies on elucidating the origin of the unexpectedly long lifetime of hot-carriers in tin-perovskite. These investigations will chiefly be carried out through time resolved photoluminescence spectroscopy on single crystals, since this technique allows for a good assessment of the carrier lifetime and single crystals tend to exhibit a higher material quality than the thin films used in devices. Compositional variation will allow for the optimisation of the hot-carrier lifetime and furthermore give rise to a deeper understanding of the atomic impacts on the lifetime.Following these fundamental studies, the carrier cooling will be optimised for thin films usable in solar cells. This especially concerns the passivation of electrical trap states at grain boundaries.In the last phase of the project, the extraction of hot-carriers is to be demonstrated. This will require to establish a proper electrical contact to the material. To this end, I propose to use low-dimensional nanomaterials, whose properties I studied during my doctoral work.Analogous to the perovskite absorption layer, all necessary contacting layers ought to be deposited from solution, to allow for a cheap and easy processing. This is a crucial requirement for the later large-scale production of solar cells.

• DFG Programme: Research Fellowships
• International Connection: Netherlands
• Host: Professorin Dr. Maria A. Loi