Optimizing Hole Transport Materials for Perovskite Solar Cells: Spiro-OMeTAD Additives, Derivatives and Substitutes

Spiro-OMeTAD (2,2',7,7'-tetrakis (N, N-di-p-methoxyphenylamine) -9,9'-spirobifluorene) has been a key hole transport material (HTM) in perovskite solar cells (PSCs) due to its excellent charge transport properties and compatibility with high-efficiency devices. However, its widespread application in PSCs is hindered by the limitations such as environmental sensitivity, high production costs, and the optimal conductivity via chemical doping process. This review explores three critical approaches to addressing these challenges: 1) the Spiro-OMeTAD-based additives and specialized treatments, including oxygen-free processes, that enhance stability and performance; 2) the development of Spiro-OMeTAD derivatives designed to improve HTM properties such as moisture resistance; 3) the exploration of Spiro-OMeTAD substitutes with cost-effectiveness and better scalability. By examining these strategies, this review provides the insights based on the traditional Spiro-OMeTAD to improve the efficiency, stability, and commercial viability of PSCs. The findings are intended to guide future research and development in the advancing PSCs technology towards broader adoption.