O3 fast and simple treatment-enhanced p-doped in Spiro-MeOTAD for CH3NH3I vapor-assisted processed CH3NH3PbI3 perovskite solar cells

We demonstrate a simple and fast post-deposition treatment with high process compatibility on the hole transport material（HTM） Spiro-MeOTAD in vapor-assisted solution processed methylammonium lead triiodide（CH3NH3PbI3）-based solar cells. The prepared Co-doped p-type Spiro-MeOTAD films are treated by O3 at room temperature for 5 min,10 min, and 20 min, respectively, prior to the deposition of the metal electrodes. Compared with the traditional oxidation of Spiro-MeOTAD films overnight in dry air, our fast O3 treatment of HTM at room temperature only needs just 10 min,and a relative 40.3% increment in the power conversion efficiency is observed with respect to the result of without-treated perovskite solar cells. This improvement of efficiency is mainly attributed to the obvious increase of the fill factor and short-circuit current density, despite a slight decrease in the open-circuit voltage. Ultraviolet photoelectron spectroscopy（UPS） and Hall effect measurement method are employed in our study to determine the changes of properties after O3 treatment in HTM. It is found that after the HTM is exposed to O3, its p-type doping level is enhanced. The enhancement of conductivity and Hall mobility of the film, resulting from the improvement in p-doping level of HTM, leads to better performances of perovskite solar cells. Best power conversion efficiencies（PCEs） of 13.05% and 16.39% are achieved with most properly optimized HTM via CH3NH3I vapor-assisted method and traditional single-step method respectively.