Halide Segregation versus Interfacial Recombination in Bromide-Rich Wide-Gap Perovskite Solar Cells

Perovskites offer exciting opportunities to realize efficient multijunction 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 (∼1.5–1.9 eV). While all wide-gap cells (≥1.69 eV) 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 nonsegregated partial cell stacks demonstrate that both transport layers (PTAA and C60) induce significant nonradiative 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 (≤1.75 eV), resulting in 20% efficient 1.7 eV bandgap cells. However, a simultaneous optimization of the p-interface is necessary to further advance larger bandgap (≥1.75 eV) pin-type cells.