Vapor assisted deposition of alkaline doped perovskites: Pure phase formation of CsxMA1−xPbI3

Abstract

Alkaline doping (Cs, Rb) in CH3NH3PbI3 (MAPbI3) is known to enhance the stability of perovskite solar cells. The films are usually deposited using anti-solvent method, which is tricky and not applicable for large scale deposition. Besides, in case of CsxMA1−xPbI3 the amount of Cs must be carefully controlled to prevent CsI phase formation. Herein, we report an atmospheric pressure vapor assisted solution process (AP-VASP) for the growth of Cs doped MAPbI3 perovskite films that features highly uniform morphology, pin-hole free films, large grain size, as well as being scalable. The CsxMA1−xPbI3 films are formed by the reaction of Cs doped PbI2 films with MAI vapor in a simple oven. We demonstrate a simple method for obtaining CsxMA1−xPbI3 films with Cs content as high as 20% without phase segregation of CsPbI3 or CsI. Impedance spectra measurements reveal that Cs incorporation into MAPbI3 increases recombination resistance, up to 83% (28 vs. 15 Ω cm2), resulting in higher open circuit voltage and efficiency. The photovoltaic performance is considerably improved by Cs doping, with the highest efficiency being 14.1% for the Cs0.1MA0.9PbI3 cells compared with 13% for the MAPbI3 ones. As expected, Cs0.1MA0.9PbI3 cells show better stability compared to MAPbI3 cells.