Synergetic Effect of Chloride Doping and CH₃ NH₃ PbCl₃ on CH₃ NH₃ PbI_3-x Cl_x Perovskite-Based Solar Cells

The chloride-doped CH₃ NH₃ PbI_3-x Cl_x perovskite has attracted great attention owing to clear performance enhancement by using a Cl additive and by the controversial arguments on Cl function and the mechanism behind it. Herein, a series of CH₃ NH₃ PbI_3-x Cl_x perovskites with various Cl content was prepared through a gas/solid reaction between CH₃ NH₂ gas and HPbI_3-x Cl_x (x=0-1). The small amount of Cl doping in CH₃ NH₃ PbI_3-x Cl_x (x=0.05) could lead to band gap broadening and significantly increase the perovskite grain size, and the phase-pure CH₃ NH₃ PbI_2.95 Cl_0.05 perovskites exhibited up to 17.44 % efficiency. For Cl contents higher than 0.1 (x>0.1), CH₃ NH₃ PbCl₃ formed and coexisted with CH₃ NH₃ PbI_3-x Cl_x , and CH₃ NH₃ PbCl₃ could help to improve the thermal stability of CH₃ NH₃ PbI_3-x Cl_x . However, the excessive co-existing wide-band-gap CH₃ NH₃ PbCl₃ perovskites would inhibit the electron transfer and lead to a deterioration of photovoltaic performance.