Strategies to improve the performance of perovskite solar cells with Spiro-OMeTAD as HTM: A comprehensive review

The performance of perovskite solar cells (PSCs) is critically influenced by the properties of the hole transport layer (HTL), with Spiro-OMeTAD remaining the most widely adopted organic hole transfer materials (HTM) due to its favorable energy levels and compatibility with perovskite absorbers. However, its intrinsic limitations-such as low conductivity, susceptibility to environmental degradation, and interfacial instability-necessitate advanced engineering strategies. This review provides a comprehensive analysis of recent innovations in chemical and physical doping techniques aimed at enhancing Spiro-OMeTAD functionality. Chemical additives, including LiTFSI, tBP, and Co-complexes, have been shown to modulate charge carrier density and mobility, while physical treatments such as UV ozone exposure and CO 2 bubbling offer environmentally stable pathways for p-type doping. Furthermore, bilayer architecture and buffer layer integration have emerged as effective methods to suppress nonradiative recombination and optimize energy level alignment at the perovskite/HTL interface. Synergistic effects from light soaking, oxygen annealing, and molecular design of composite structures have led to significant improvements in power conversion efficiency and operational stability. By critically evaluating these strategies, this review lays the groundwork for the rational design of next-generation HTLs and highlights the pivotal role of Spiro-OMeTAD engineering in advancing the commercial viability of PSCs. • Comprehensively evaluates dopant, additive, and interfacial engineering strategies to optimize Spiro-OMeTAD for high-performance PSCs. • Summarizes recent chemical and physical doping approaches, including emerging oxidation pathways. • Strategies to suppress dopant diffusion, Li + migration, and over-oxidation that limit device operational stability. • Provides a perspective on advances, remaining challenges, and future research directions for Spiro-OMeTAD in PSCs.