Effects of guanidinium cations on structural, optoelectronic and photovoltaic properties of perovskites

Guanidinium (GA) cations are intentionally introduced in MAPbI 3 perovskite by considering its potential capability of stabilizing the material through plenty of hydrogen bonds and mitigating hysteresis because of the zero dipole moment. The configurations of GA cation in film and its effects on structural, optoelectronic and photovoltaic properties of perovskite have been comprehensively studied by systematically modulating the GA ratio. It has been demonstrated that moderate GA cations can effectively passivate the defect surrounding perovskite grains, yielding an enhanced efficiency as high as ~19.2% in a p-i-n type planar solar cells with the GA ratio of 15%. Further increasing the GA ratio deteriorates device performance, as extra GA cations hinder grain growth and thus reduce the grain size, which facilitates the defect generation around the enhanced interface. Moreover, a new two-dimensional (2D) layered perovskite phase that features alternating GA and MA cations in the interlayer space (ACI) appears ultimately, while the ACI phase typically suffers from slow charge transportation across the parallel PbI 2 octahedral layers separated by large A-site cations.