Ultrasensitive Heterojunctions of Graphene and 2D Perovskites Reveal Spontaneous Iodide Loss

Despite the demonstrated high efficiency of perovskite solar cells and light-emitting devices, the understanding of the intrinsic stability of perovskites is far from complete. In this work, using an ultrasensitive, exfoliated 2D perovskite single-crystal sheet/graphene heterostructure device, we reveal spontaneous iodide loss as an important degradation pathway of 2D perovskite single crystals, which n-dopes the perovskite semiconductor by generating positively charged iodide vacancies. Furthermore, we show that covering perovskites with graphene can suppress the iodide loss, significantly improving perovskite stability. A perovskite phototransistor is demonstrated with a graphene/2D perovskite/graphene structure, which shows no degradation after 75 days. Our work not only provides important insights for future stable perovskite optoelectronic device development, but also demonstrates the potential of graphene as a promising sensitive diagnostic tool for device and material degradation studies. Metal halide perovskites have achieved remarkable success in lab-scale solar cells and light-emitting devices. However, instability issues impede their practical use. Various degradation paths of polycrystalline perovskites have been revealed under a range of external environmental stresses such as light, heat, and moisture. However, the understanding of the intrinsic stability of perovskites is far from complete. Here, we reveal spontaneous iodide loss as an important degradation path of 2D perovskite single crystals, enabled by an ultrasensitive, exfoliated 2D perovskite single-crystal sheet/graphene heterostructure device. Furthermore, covering perovskites with a graphene overlayer can suppress iodide loss, significantly improving perovskite stability. Our work provides important insights for future stable perovskite optoelectronic device development and demonstrates the potential of graphene as a promising diagnostic tool for device and material degradation. Using an ultrasensitive, exfoliated 2D perovskite single-crystal sheet/graphene heterostructure device, spontaneous iodide loss is revealed as an important degradation pathway of perovskites, which n-dopes perovskites by generating positively charged iodide vacancies. Furthermore, covering perovskites with graphene can suppress iodide loss, significantly improving perovskite stability. Our work not only provides important insights for future stable perovskite optoelectronic device development, but also demonstrates the potential of graphene as an encapsulant as well as a sensitive diagnostic tool for device and material degradation studies.