Working Principle of Integrated Perovskite-Organic Solar Cells

While perovskite-organic tandem solar cells have gained significant attention for their potential to achieve high efficiencies and stability, a somewhat similar class of devices, termed "integrated" solar cells, has emerged. These devices differ by processing the bulk-heterojunction directly atop the perovskite without intermediate charge transport or interconnecting layers. Numerous reports continue to highlight increasing efficiencies, while the underlying mechanisms are often misunderstood. As a result, there are persistent claims that such integrated cells benefit from the extension of the spectral absorption or might even offer a pathway to surpass the detailed-balance limit of single-junctions. To evaluate their photovoltaic potential, here, we provide the first comprehensive explanation of the operation principle of these integrated perovskite-organic cells. Unlike tandem devices, which are connected in series through an interconnect, integrated cells are a parallel connection of the subcells, where the organic subcell comprises a charge extraction barrier. Our model accurately reproduces device characteristics from both our lab and the literature. Validation through subcell-selective characterization and drift-diffusion simulations confirms its applicability. We reveal that the hole extraction barrier in the organic subcell cannot be overcome without compromising the overall device performance. Integrated devices are, therefore, single-junction devices that cannot rival tandem devices in surpassing the detailed-balance limit.