B-site doping of CsPbI3 quantum dot to stabilize the cubic structure for high-efficiency solar cells

We have explored that the phase transition of colloidal perovskite CsPbI3 quantum dot (QD) during synthesis and purification processes are mainly induced by the increase of particle size (crystal growth). To stabilize the cubic structure, the metal cations Mn2+ and Zn2+ with smaller ion radius than that of Pb2+ were doped into the QD. These not only caused the lattice constriction and increased the Goldschmidt tolerance factor of perovskite structure, but also enhanced the Pb-I binding energy, all of which improve the tolerance of phase transition induced by the growth of crystal size during purification process. Besides, the doped QD solutions and films show fewer defects and lower trap density than those of the undoped samples, owing to the alleviation of lattice distortion. The results reveal that the Zn-doped and Mn-doped QD solar cells display power conversion efficiency of 13.5% and 12.0%, respectively, much higher than that of the control device.