High‐Performance Planar Solar Cells Based On CH 3 NH 3 PbI 3‐ x Cl x Perovskites with Determined Chlorine Mole Fraction

Solution‐processable hybrid perovskite solar cells are a new member of next generation photovoltaics. In the present work, a low‐temperature two‐step dipping method is proposed for the fabrication of CH 3 NH 3 PbI 3‐ x Cl x perovskite films on the indium tin oxide glass/poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) substrate. The bandgaps of the CH 3 NH 3 PbI 3‐ x Cl x perovskite films are tuned in the range between 1.54 and 1.59 eV by adjusting the PbCl 2 mole fraction ( n Cl /( n Cl + n I )) in the initial mixed precursor solution from 0.10 to 0.40. The maximum chlorine mole fraction measured by a unique potentiometric titration method in the produced CH 3 NH 3 PbI 3‐ x Cl x films can be up to 0.220 ± 0.020 ( x = 0.660 ± 0.060), which is much higher than that produced by a one‐step spin‐coating method (0.056 ± 0.015, x = 0.17 ± 0.04). The corresponding solar cell with the CH 3 NH 3 PbI 2.34±0.06 Cl 0.66±0.06 perovskite film sandwiched between PEDOT:PSS and C 60 layers exhibits a power conversion efficiency as high as 14.5%. Meanwhile, the open‐circuit potential ( V oc ) of the device reaches 1.11 V, which is the highest V oc reported in the perovskite solar cells fabricated on PEDOT:PSS so far.