Method to Inhibit Perovskite Solution Aging: Induced by Perovskite Microcrystals

Abstract

The main feature of perovskite solar cells (PSCs) is that the perovskite layer can be fabricated by the solution method, while the long-time stability of the precursor solution is critical. During the fabrication of formamidinium (FA)-based PSCs, the introduction of methylammonium cations (MA+) in the precursor solution can accelerate the crystallization process of the perovskite layer, stabilize the perovskite structure, and passivate defects. However, MA+ is easy to deprotonate to generate MA molecules, and it then condensates with formamidinium iodide (FAI) to form adverse byproducts. Herein, perovskite microcrystals (MCs) for preparing perovskite precursor solution were investigated in details, which can improve the long-term stability of the precursor solution and the perovskite film. We found that FA+ in MC solution was confined in the three-dimensional scaffold, preventing it from reacting with MA+. Meanwhile, MCs can effectively promote nucleation to form large grains in perovskite films. The photoelectric conversion efficiency (PCE) of the device with 3 week-aged MC solution remains at 90% and is only reduced by 10% after 160 h of continuous operation, which far exceeds the performance of the PCE of those based on mixed monomer powder (MP) solution. Therefore, perovskite MCs, an effective reactive inhibitor to improve the stability of perovskite precursor solutions, are of great significance for large-scale commercial fabrication.

Unraveling the Influence of Solvent on Side Reactions between Formamidinium Lead Triiodide and Methylammonium Cations

“…It is worth noting that we employ FAPbI 3 single crystals to prepare the precursor solution instead of using FAI and PbI 2 . This choice minimizes the influence of impurities in PbI 2 . , The precursor solution undergoes aging in a glovebox with inert nitrogen gas at room temperature (25 °C), effectively eliminating the influence of external environmental factors such as water, oxygen, and temperature. ESI-MS technology is used to detect the reaction products of the aging solution …”

“…Several factors affect the reactivity of FAPbI 3 perovskites in the presence of MA + cations. First, temperature is the most critical factor affecting the deprotonation of MA + ; higher temperatures promote the deprotonation of MA + . , Second, alkaline impurities in PbI 2 have also been found to be important factors in inducing deprotonation and subsequent reactions. , However, some studies have reported that Lewis base additives could stabilize the precursor solution and inhibit the generation of MFAI. ,,, At the same time, other literatures persist that Lewis acid additives could inhibit the generation of MFAI. ,, These results indicate that the aging mechanism of the FAPbI 3 perovskite precursor solution is still very complex and unclear. Another factor that cannot be ignored for the aging of the precursor solution is the solvent itself.…”

Growth mechanism of metal halide perovskite single crystals in solution

“…Short-term and long-term stability of precursors is critical in perovskite solution systems. [58][59][60] On the one hand, aging of the precursor affects the crystallinity of the MHP SCs. It has been reported that with the increase of aging resistance time of precursor solution, the colloid clusters in solution can maintain a larger volume for a long time.…”

By adding different perovskite seeds to obtain high-quality perovskite films

“…Spin-coating process is relatively simple, which is the current method of perovskite light absorption layer. According to the different steps can be further divided into one-step process [4][5][6] , and two-step process [7,8] . Among them, the one-step process refers to add all the raw materials of perovskite into the solvent, and then form the precursor solution after completely dissolved.…”