Proceedings of Materials for Sustainable Development Conference (MAT-SUS) (NFM22)
DOI: https://doi.org/10.29363/nanoge.nfm.2022.059
Publication date: 11th July 2022
All-perovskite tandem solar cells promise high photovoltaic performance at low cost. So far however, their efficiencies cannot compete with traditional inorganic multi-junction solar cells and they generally underperform in comparison to what is expected from the isolated single junction devices. Understanding performance losses in all-perovskite tandem solar cells is a crucial aspect that will accelerate advancement. Here, we perform extensive selective characterization of the individual sub-cells to disentangle the different losses and limiting factors in these tandem devices. We find that non-radiative losses in the high-gap subcell dominate the overall recombination losses in our baseline system as well as in the majority of literature reports. We consecutively improve the high-gap perovskite subcell through a multifaceted approach, allowing us to enhance the open-circuit voltage (VOC) of the subcell by up to 120 mV. Due to the (quasi) lossless indium oxide interconnect which we employ for the first time in all-perovskite tandems, the VOC improvements achieved in the high-gap perovskites translate directly to improved all-perovskite tandem solar cells with a champion VOC of 2.00 V and a stabilized efficiency of 23.7%. The efficiency potential of our optimized all-perovskite tandems reaches 25.2% and 27.0% when determined from electro- and photo-luminescence respectively, indicating significant transport losses as well as imperfect energy-alignment between the perovskite and the transport layers in the experimental devices. Further improvements to 28.4% are possible considering the bulk quality of both absorbers measured using photo-luminescence on isolated perovskite layers. Our insights therefore not only show an optimization example but a generalizable evidence-based strategy for optimization utilizing optical sub-cell characterization.