Halogen-free guanidinium-based perovskite solar cell with enhanced stability

Herein, we report a new halogen-free and excellent stable perovskite, GAPb(SCN)₃, which was prepared from the symmetric guanidinium cation (GA⁺) with nearly zero dipole moment, and pseudohalogen (SCN^-), for the fabrication of stable perovskite solar cells. GAPb(SCN)₃ exhibits an orthorhombic crystal phase, with optical band gap of 1.43 eV. The orthorhombic crystal phase shifted to a cubic phase, due to the formation of PbS beyond 150 °C. GAPb(SCN)₃ itself showed excellent stability upon being exposed to ambient conditions for 30 days, without degradation of its optical or crystallographic properties. This superior stability could be attributable to the strong electrostatic interaction between SCN^- and Pb²⁺, and hydrogen bonding between SCN^- and GA⁺. Even though it has a suitable band gap, it exhibited a significantly lower efficiency of ca. 0.11%. The very low performance could be attributable to the significantly low light absorption coefficient, and large non-radiative recombination of photo-induced charges via an oxidized form of S at the TiO₂/perovskite interface.