Enhanced perovskite electronic properties via A-site cation engineering

Organic-inorganic halide perovskites have emerged as excellent candidates for low-cost photovoltaics and optoelectronics. While the predominant recent trend in designing perovskites for efficient and stable solar cells has been to mix different A-site cations, the role of A-site cations is still limited to tune the lattice and bandgap of perovskites. Herein we compare the optoelectronic properties of acetamidinum (Ace) and guanidinium (Gua) mixed methylammonium lead iodide perovskites and shed a light on the hidden role of A-site cation on the carrier mobility of mixed-cation lead iodide perovskites. The cations do not affect the bandgap of the perovskites since the orbitals from Ace and Gua do not contribute to the band edges of the material. However, the mobility of the Ace mixed perovskite is significantly enhanced to be an order of magnitude higher than that of the pristine perovskite. We apply the Ace mixed perovskite in hole-conductor-free printable mesoscopic perovskite solar cells and obtain a stabilized PCE of over 18% (certified 17.7%), which is the highest certified efficiency so far.