Green Solvent Accelerates Spiro-OMeTAD Oxidation for Efficient Perovskite Solar Cells

As one of the most widely used hole transport materials (HTMs) in optoelectronics devices, 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9-spirobifluorene (spiro-OMeTAD) has endowed perovskite solar cells (PSCs) with record power conversion efficiencies (PCEs). However, the long oxidation time in the ambient atmosphere is time-consuming. Furthermore, commonly used solvents for spiro-OMeTAD film processing such as chlorobenzene (CB) are toxic, which severely hinders the commercialization of PSCs. Herein, ethyl acetate (EA) serves as a superior green solvent alternative to the typical processing solvent, which substantially reduces the oxidation time of spiro-OMeTAD. Without postoxidation treatment and any other additional oxidizing agents, the resultant device delivers a high PCE of 23.3%, significantly outperforming the CB-based device. It is also the highest efficiency obtained from nonhalogenated solvent-processed spiro-OMeTAD. The electrostatic potential mapping demonstrates that the electron density at nitrogen atoms of EA-processed spiro-OMeTAD is more delocalized, leading to a faster oxidation. Furthermore, the processing solvent EA is a green solvent with low toxicity, and the amount of HTMs used in the fabrication of solar cells can be dramatically reduced. This study provides a new solution for processing spiro-OMeTAD, which is ideal for the mass production of PSCs. A simple and efficient method for accelerating the oxidation process of spiro-OMeTAD is presented. By simply replacing the conventional processing solvent chlorobenzene with ethyl acetate, the oxidation process time is substantially reduced. Without postoxidation treatment and any other additional oxidizing agents, a high PCE of 23.3% is achieved, which marks the highest efficiency obtained from nonhalogenated solvent-processed spiro-OMeTAD.image (c) 2023 WILEY-VCH GmbH