Enhanced performance of CH3NH3PbI3−x Cl x perovskite solar cells by CH3NH3I modification of TiO2-perovskite layer interface

In this work, perovskite solar cells (PSCs) with CH 3 NH 3 PbI 3- x Cl x as active layer and spiro-OMeTAD as hole-transport media have been fabricated by one-step method. The methylammonium iodide (CH 3 NH 3 I) solution with different concentrations is used to modify the interface between mesoporous TiO 2 (meso-TiO 2 ) film and CH 3 NH 3 PbI 3− x Cl x perovskite layer. Several techniques including X-ray diffraction, scanning electron microscopy, optical absorption, electrochemical impedance spectroscopy (EIS) and photoluminescence are used to investigate the effect of the interfacial modification. It is found that the interfacial modification by CH 3 NH 3 I enhance the crystallinity and increase the grain size of CH 3 NH 3 PbI 3− x Cl x layer, and improve the surface wetting properties of perovskite precursor on meso-TiO 2 film. The sunlight absorption and external quantum efficiency of PSCs in the visible region with wavelength less than 600 nm have been improved. The Nyquist plots obtained from the EIS suggest that the CH 3 NH 3 I modification can reduce the charge recombination rates. The photoluminescence measurement shows that the exciton dissociation in the modified devices is more effective than that in the control samples. The photovoltaic performance of the modified devices can be significantly improved with respect to the reference (control) devices. The CH 3 NH 3 I modified devices at the optimized concentration demonstrate the average power conversion efficiency of 12.27 % in comparison with the average efficiency of 9.68 % for the reference devices.