Modifying Additive Engineering with 2D-MXene in Perovskite Layer for Highly Efficient Inverted Perovskite Solar Cells Exceeding 23% Efficiency

Abstract

On account of the excellent photovoltaic properties and solution processability of the perovskite, a number of studies have been conducted on the perovskite as a next-generation solar cell. The rapid increase of the power conversion efficiency (PCE) of the perovskite solar cells (PSCs) has been achieved in the last decade, however, it has been implemented only in the conventional (n-i-p) structure of the PSCs. The inverted (p-i-n) structure, which has low-temperature processability, negligible hysteresis effects, and better device stability than n-i-p structure, is in the spotlight. Furthermore, p-i-n structure is suitable for fabricating tandem solar cells that can overcome the Shockley-Queisser limit (S-Q limit) of single junction solar cell. In order to catch up with the efficiency of the n-i-p structure, numerous efforts have been made in the p-i-n structure. Due to the ionic nature of perovskite, which generates defect states, a typical method is to use an additive to passivate the defects in the perovskite layer. The perovskite crystal can be passivated during crystal growth process with incorporated additive or prevent halide ion migration which leads to decrease efficiency of solar cells and device stability with placing additive material between perovskite and electron transporting layer (ETL). A new family of 2D materials, called MXene, has emerged as a great candidate for additives in PSCs replacing other materials due to its outstanding electrical conductivity, tunable optical properties, and robust physical, chemical properties. Since MXene’s surface has negatively charged groups (e.g. -OH, -O, -F, and -Cl), it is reasonable to expect that interaction of MXene with Pb2+ ion in perovskite not only passivates the defect sites of the perovskite but also affects to the crystal growth of perovskite. Moreover, MXene would decrease the charge transfer resistance in PSCs by its high electrical conductivity, increase the thermal stability by its good thermal conductivity. Lastly, incorporation of MXene in the perovskite cause the change of work function of perovskite to improve the device performances. Herein, we demonstrate the affect of MXene as an additive in the p-i-n PSCs by engineering two different incorporating methods. We compared the difference in the mechanism of each crystal growth when MXene is added by two different methods, following compare the differences in morphology of perovskite and device performance according to each method. Consequently, the short-circuit current density (Jsc) and open-circuit voltage (Voc) are greatly improved, so that obtain over 23% of PCE.