Despite the remarkable progress in perovskite optoelectronic devices, the realization of high-performance and stable devices based on low-bandgap mixed lead (Pb)-tin (Sn) halide remains highly challenging. Here we present a promising strategy to improve the performance and stability of mixed lead-tin halide perovskite photovoltaics by using metal-organic frameworks (MOFs) as additives, including UiO-66 and UiO-66-NH2. Compared with UiO-66, the electron-donating amine group of UiO-66-NH2 can interact with under-coordinated metal cations in the perovskite crystals (i.e., Pb2+ or Sn2+), leading to efficient trap-state passivation and thus superior device performance. With interfacial engineering via molecular doping, the resultant devices exhibit a high-power conversion efficiency of 13.93% and substantially improved ambient stability. To the best of our knowledge, the device performance demonstrated herein represents the highest value ever reported for CH3NH3SnxPb1−xI3-based perovskite solar cells with an active area larger than 0.1 cm2. Importantly, this strategy is also applicable to perovskite photodetectors (PDs), delivering record-high performance for low-bandgap (≤1.3 eV) perovskite PDs. This work provides a new route to simultaneously improve the performance and stability of mixed Pb-Sn perovskite photovoltaics based on a facile strategy, which can accelerate perovskite-based optoelectronics toward future commercialization.