Direct interface engineering using dopant of hole transport layer for efficient inorganic perovskite solar cells

With respect to the aim of achieving a suitable optical band gap and high thermal and chemical stability in next-generation perovskite solar cells (PSCs), inorganic CsPbI₃ perovskite has gained significant attention. However, when it absorbs light, it quickly transforms into an undesired nonperovskite yellow phase at 25 °C. Therefore, it is crucial to stabilize the phase by reducing the defect density, which acts as a nonradiative recombination center at the interface of each layer. In this paper, we present an efficient interface treatment method that does not require any additional surface treatment such as annealing or coating, and the dopant Mn(TFSI)₂ is directly mixed with the hole transporting material instead of bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI). The use of Mn(TFSI)₂ as a dopant diminishes the interfacial defects between the perovskite and hole transporting layer, reducing nonradiative recombination, increasing the lifetime of the carrier, and improving the power conversion efficiency from 16.5% for the control device using conventional Li-TFSI as a dopant to 17.6%. Moreover, the Mn(TFSI)₂-doped device demonstrates superior long-term stability for 1000 h under ambient conditions without encapsulation, demonstrating 95% efficiency when compared with the initial performance. Therefore, Mn(TFSI)₂ is a more powerful dopant of HTL and can increase the power conversion efficiency of PSCs by passivating the interface between the perovskite and HTL. Using Mn(TFSI)₂, it is possible to quickly and effectively manufacture a stable inorganic perovskite device.