Molecular Design of Metal Phthalocyanines with Strong Electron-Donating Substituents for Perovskite Solar Cells

Abstract

Perovskite solar cells have recently revolutionized the field of the emerging photovoltaic technologies, showing an impressive evolution in the last ten years jumping from an initial 3.8%1 to a 22.1%2 certified efficiency. Nonethless, there are still ongoing challenges to face in order to foresee their commercialization, some of which are related to the use of the expensive Spiro-OMeTAD as hole transport material (HTM) and to the active layer morphology, whose inhomogeneity can promote low-resistance shunting paths, loss of light absorption and perovskite degradation in the solar cells, undermining their photovoltaic performances and stability during time. Phthalocyanines are macrocyclic aromatic compounds that can potentially address both the issues: their p-type semiconducting properties make them appealing materials as hole transporters and at the state of the art, they have scored very high efficiencies3-4 in perovskite-based devices. Furthermore, they are potentially effective as surface passivants, reducing the active layer pinholes and increasing both stability and performances of the corresponding devices, because of their excellent thermal and chemical stability, hydrophobic carbon-based core and good processability within the solar cells. With the aim of addressing both the issues individually, in this contribution we will discuss our synthetic strategies for the preparation of several metal phthalocyanines, conveniently functionalized with strong electron-donating substituents and suitable functional groups, along with our first results of their implementation in perovskite-based devices.