Tailoring solubility of methylammonium lead halide with non-stoichiometry molar ratio in perovskite solar cells: Morphological and electrical relationships for high current generation

Abstract

Recent studies have shown a highly efficient performance of perovskite solar cells (PSCs) of 22.7%. Although a number of efforts have been made to reproduce flat, uniform, and dense perovskite films using a stoichiometric ratio of 'CH(3)NH(3)l: PbI2: DMSO = 1:1:1', several complicated processes are required to achieve a regular grain-to-grain uniformity. Therefore, it was difficult to reproduce. This is because the conventional ratio of 'CH3NH3I: PbI2: DMSO = 1:1:1' can cause the CH3NH3I-PbI2-DMSO intermediate phase and the CH3NH3PbI3 crystal phase to coexist in solution. As a result, the CH3NH3PbI3 crystals in the solution may deteriorate the quality of the thin film. In this study, the non-stoichiometric molar ratio among CH3NH3I:PbI2:DMSO solutions was applied to control the quality of the perovskite layers. We successfully fabricated uniform and dense CH3NH3PbI3 PSCs, by simply manipulating CH3NH3PbI3 solubility with the different DMSO molar amounts. Further, a homogeneous grain size and a regular inter-grain arrangement with scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses were obtained in the optimized solubility. We also confirmed that the PSCs with the optimized condition exhibited higher J(sc) (Current density) and PCE (Power Conversion Efficiency), due to the Lamer model effect on the enhancement of the internal light absorption. Furthermore, the device with the optimized solubility exhibited enhanced electrical properties. Especially, the improved-electrical properties of the charge carrier-separation, mobility, collection, generation, and resistances were confirmed by photoluminescence (PL) quenching/mapping of the space-charge limited current (SCLC), the photo current density as a function of internal voltage (J(ph)-V-int) characteristic, and the impedance. Consequently, it was shown that tailoring the solubility of CH3NH3PbI3 can have a critical effect on the production of high quality perovskite thin films. These films will have an appropriate particle size and uniformity that will have a promising approach for generating high current densities.