Proceedings of Online School on Fundamentals of Emerging Solar Cells (PVSCHOOL)
Publication date: 29th January 2021
Perovskites offer exciting opportunities to realise efficient multi-junction photovoltaic devices. This requires high-VOC and often Br-rich perovskites which currently suffer from halide segregation. Here, we study triple-cation perovskite cells over a wide bandgap-range (~ 1.5-1.9eV). While all wide-gap cells (≥1.69eV) experience rapid phase segregation under illumination, the electroluminescence spectra are less affected by this process. The measurements reveal a low radiative efficiency of the mixed halide phase which explains the VOC-losses with increasing Br-content. Photoluminescence measurements on non-segregated partial cell stacks demonstrate that both transport layer (PTAA and C60) induce significant non-radiative interfacial recombination, especially in Br-rich (>30%) samples. Therefore, the presence of the segregated iodide-rich domains is not directly responsible for the VOC-losses. Moreover, LiF can only improve the VOC of cells that are primarily limited by the n-interface (≤1.75eV) resulting in 20% efficient 1.7eV bandgap cells. However, a simultaneous optimization of the p-interface is necessary to further advance larger bandgap (≥1.75eV) pin-type cells.