(Invited) Hole-Transporting Materials for Perovskite Solar Cells: A Theoretical Insight

Hole-transporting materials (HTMs) are a crucial component in obtaining high power conversion efficiencies (PCEs) in perovskite-based solar cells (PSCs). They play the important roles of extracting the photogenerated holes, formed within the perovskite film, and transporting them to the electrodes. Among the wide number of chemical structures proposed as HTMs for PSCs, small organic molecules have received special attention with spiro-OMeTAD (2,2´,7,7´-tetrakis( N , N -di- p -methoxyphenylamine)-9,9´-spirobifluorene) as a reference. 1 In this communication, we first focus on how the donor ability and hole reorganization energy change with the chemical structure of the HTM. Sulfur-rich compounds, such as the anthracene-tetrathiophene ATT-OMe system displayed in Figure 1a, that have been used as HTMs in PSCs achieving remarkable PCEs, are theoretically described. 2 Second, we investigate a series of HTMs based on fused polyheteroaromatic molecules incorporating 7-azaindole terminal moieties bearing hydrogen-bond donor and hydrogen-bond acceptor sites (Figure 1b). The 7-azaindole units induce the hydrogen-bond self-assembly of the conjugated molecules thus increasing the supramolecular ordering in the HTM layer. The effects of this ordering on the charrier transport in the HTM semiconducting layer are theoretically discussed. 3 Third, we briefly present how the optical properties (energy bandgap) of Cs 2 AgBiBr 6 lead-free double perovskites can be tuned by substituting the monovalent Ag 1+ and trivalent Bi 3+ cations by divalent Sn 2+ , Ge 2+ and Zn 2+ cations. 4 Figure 1. Chemical structure of the sulfur-rich ATT-OMe (a) and the H-bond-promoting ADAI (b) HTM molecules. Both HTMs are based on an anthracene central core. References J. Urieta, I. García-Benito, A. Molina-Ontoria, N. Martín, Chem. Soc. Rev. 2016 , 47 , 8541. I. Zimmermann, J. Urieta-Mora, P. Gratia, J. Aragó, G. Grancini, A. Molina-Ontoria, E. Ortí, N. Martín, M. K. Nazeeruddin, ACS Appl. Mater. Interfac. 2017 , 7 , 1601674. P. Gómez, S. Georgakopoulos, M. Más-Montoya, J. Cerdá, J. Pérez, E. Ortí, J. Aragó, D. Curiel, J. Mater. Chem. C 2021 , 13 , 8620. P. Sebastiá-Luna, J. Calbo, N. Albiach-Sebastián, M. Sessolo, F. Palazón, E. Ortí, H. J. Bolink, Chem. Mater. 2021 , 33 , 8028. Figure 1