Two-Dimensional Perovskite Quantum Dot Building Blocks toward Efficient 2D/3D Perovskite Heterostructures in Photovoltaics.

Two-dimensional/three-dimensional (2D/3D) perovskite solar cells (PSCs) have attracted considerable attention due to their promising performance and environmental stability. However, conventional in situ grown 2D/3D perovskites form a layered structure with 2D organic spacer layers aligned parallel to the 3D perovskite, impeding out-of-plane carrier transport. Moreover, the distinct cation size between 2D and 3D perovskites triggers ion diffusion at the heterointerface, leading to the formation of a mixed-phase 2D perovskite and increased defect density, which severely limits device performance. To address these issues, we synthesized 2D perovskite quantum dots (QDs) modified with poly(3-hexylthiophene) (P3HT), acting as building blocks, which were subsequently deposited onto a 3D perovskite film to construct novel 2D QDs@P3HT/3D PSCs. This strategy effectively suppresses defect accumulation caused by mixed phases in traditional 2D/3D perovskite. Furthermore, this design facilitates additional vertical carrier transport pathways, alleviating the out-of-plane carrier transport limitation in conventional layered 2D/3D perovskite. As a result, the optimized devices achieve a power conversion efficiency of 25.04% and exhibit remarkable stability, retaining over 93% of their initial efficiency after 1200 h of aging under 85% relative humidity at 25 °C. This work offers a viable strategy to balance efficiency and stability in perovskite photovoltaics.