Highly Efficient Monolithic Perovskite/TOPCon Silicon Tandem Solar Cells Enabled by “Halide Locking”

Perovskite/silicon tandem solar cells (TSCs) are promising candidates for commercialization due to their outstanding power conversion efficiencies (PCEs). However, controlling the crystallization process and alleviating the phases/composition inhomogeneity represent a considerable challenge for perovskite layers grown on rough silicon substrates, ultimately limiting the efficiency and stability of TSC. Here, this study reports a "halide locking" strategy that simultaneously modulates the nucleation and crystal growth process of wide bandgap perovskites by introducing a multifunctional ammonium salt, thioacetylacetamide hydrochloride (TAACl), to bind with all types of cations and anions in the mixed halide perovskite precursor. The approach not only enables excellent compositional uniformity in the wet-film stage but also induces preferred orientation along the (001) plane following nucleation, leading to enhanced homogeneity of the perovskite film in both vertical and horizontal directions over long-length scales. The resulting wide-bandgap perovskite solar cells yield exceptional open-circuit voltage-fill factor products (V_OC × FF) of 1.074 and 1.040 in small- (0.0414 cm²) and large-area (1.0208 cm²) devices, respectively. Corresponding large-area tandem solar cells based on the Tunnel Oxide Passivated Contact (TOPCon) silicon subcells achieve a record PCE of 31.32% with a remarkable V_OC of 1.931 V and FF of 81.54%.