The Effect of Lithium Doping in Solution-Processed Nickel Oxide Films for Perovskite Solar Cells

The effect of substitutional Li doping into NiO_x hole transporting layer (HTL) for use in inverted perovskite solar cells was systematically studied. Li doped NiO_x thin films with preferential crystal growth along the (111) plane were deposited using a simple solution-based process. Mott-Schottky analysis showed that hole carrier concentration (N_A ) is doubled by Li doping. Utilizing 4 % Li in NiO_x improved the power conversion efficiency (PCE) of solar devices from 9.0 % to 12.6 %. Photoluminescence quenching investigations demonstrate better hole capturing properties of Li:NiO_x compared to that of NiO_x , leading to higher current densities by Li doping. The electrical conductivity of NiO_x is improved by Li doping. Further improvements of the device were made by using an additional ZnO layer onto PCBM, to remove shunt paths, leading to a PCE of 14.2 % and a fill factor of 0.72.