Perovskite solar cells: Li-TFSI and t-BP-based chemical dopant engineering in spiro-OMeTAD

Organic-inorganic lead halide perovskite solar cells (PSCs) offer promising aspects such as high efficiency, low-cost, and flexible. The booming growth of PSCs cannot be achieved without the application of chemical dopant engineering. The hole-transporting layer (HTL) in PSCs are critical for predicting device performance and are a major bottleneck for further improving device stability and efficiency. Li-TFSI/t-BP, which are widely used in the doping of hole-transporting materials (HTMs), are essential for the preparation of high-performance devices, and although many novel dopants have been reported, the state-of-the-art devices are still based on this bi-doping system. This review summarizes the latest advances in the modification of the Li-TFSI/t-BP bi-doping system in PSCs. It systematically presents the mechanism of Li-TFSI/t-BP doping of spiro-OMeTAD and the major factors affecting this doping reaction. The modification strategy of the Li-TFSI/t-BP bi-doping system and the application of co-dopant in this system have been focused on. In addition, the selection of doping methods for different doping systems, mainly divided into liquid-liquid, liquid-solid, and gas-solid contact doping methods, is briefly introduced. Finally, the corresponding design principles of the doping system and the subsequent development perspectives in this field are discussed in detail.