Spiro-Phenothiazine Based Hole-Transporting Materials for Highly Efficient and Stable Perovskite Solar Cells

Perovskites solar cells (PSCs) have emerged, since 2009, as the most promising technology to replace/complement crystalline silicon PV. [1] Outstanding results of PCE up to 26.7 % have been obtained using perovskites (eg. MAPbI 3 ) in just a few years of research. The continuous improvement of the efficiency in PSCs has been achieved using commercially available spiro-OMeTAD as hole-transporting material (HTM). However, spiro-OMeTAD is an expensive material due to its difficult purification and multi-step synthetic protocols (in harsh conditions) which limits its future use in large-scale applications. As a consequence, great efforts in the synthesis and characterization of alternative organic low-cost molecules for its application as HTMs have been reported in the recent years, including PAH-based, spiro-containing or dopant-free materials. [2] Our research group reported two doped-HTMs based on electron-rich spiranic scaffolds, namely, spiro-POZ and spiro-PTZ which exhibit a similar performance of the reference material and improved long-term stability (more than 300 days of exposure to ambient conditions and more than 1200 h under continuous 1 sun illumination) in sharp contrast with the reference of spiro-OMeTAD. [3] Motivated by these excellent results, we have designed four new derivatives based on spiro-PTZ functionalized with asymmetric diphenylamine units that have been incorporated in PSCs improving the PCE of the devices up to 25.75%, surpassing clearly the power conversion efficiency and stability of spiro-OMeTAD. Furthermore, large area mini module (25 cm 2 ) also shows an outstanding PCE above 22%, pointing spiro-PTZ derivatives as one of the most efficient HTMs reported in bibliography. References [1] A. Kojima, K. Teshima, Y. Shirai, T. Miyasaka, J. Am. Chem. Soc. 2009 , 131 , 6050-6051. [2] J. Urieta-Mora, I. García-Benito, A. Molina-Ontoria, N. Martín, Chem. Soc. Rev. 2018 , 47 , 8541-8571. [3] J. Urieta-Mora, I. García-Benito, L.-A. Illicachi, J. Calbo, J. Aragó, A. Molina-Ontoria, E. Ortí, N. Martín, M. K. Nazeeruddin, Sol. RRL 2021 , 5 , 2100650. Figure 1