Modulation of SpiroOMeTAD Hole-Transport Layers for Carbon-Based Perovskite Solar Cells

Carbon-based perovskite solar cells (C-PSCs) exhibit superior stability, yet their power conversion efficiencies are often constrained by inefficient charge carrier transport and collection, leading to significant energy losses in charge transfer dynamics. The hole transport layer (HTL) is pivotal for enhancing C-PSC performance; however, its intrinsic deficiencies, such as low conductivity and poor interfacial properties, necessitate precise modulation of both electrical characteristics and interface contacts. This review focuses on recent advancements in modulating HTLs, particularly through doping strategies and other methods aimed at improving electrical properties and interfacial engineering in C-PSCs. We place special emphasis on the practical application progress of carbon nanomaterials, particularly asymmetric carbon nanohorns (ACNHs), in modifying Spiro-OMeTAD-based HTLs for C-PSCs, highlighting their role in enhancing conductivity, reducing hysteresis, and improving long-term stability. This work summarizes recent material innovations, functionalization approaches, and underlying mechanisms, providing insightful perspectives for developing high-performance and durable HTLs for next-generation C-PSCs.