On the Role of Carboxylated Polythiophene in Defect Passivation of CsPbI 2 Br Surface for Efficient and Stable All‐inorganic Perovskite Solar Cells

Improved film surface is a prerequisite to achieve high photovoltaic performance of inorganic perovskite solar cells because defective (under-coordinated) lead ions derived from imperfect lattice structure of the film surface or grain boundaries the principal nonradiative recombination centers in the inorganic perovskite absorber. In this study, we suggest poly[3-(4-carboxybutyl)thiophene-2,5-diyl] (P3CT), a carboxylated p-type conjugated polymer, as a passivating agent of the CsPbI2Br layer to tailor electronic properties of a perovskite absorber. With the P3CT passivation, the defective sites of the perovskite film surface were improved and stabilized, which can suppress nonradiative recombination to promote charge transport of CsPbI2Br-based all-inorganic perovskite solar cells. Consequently, the P3CT passivation delivers a power conversion efficiency (PCE) of 12.25% and decent long-term stability of CsPbI2Br perovskite solar cells, which surpasses the pristine device without the passivation. The electricity generation capability under indoor light source of the passivated device is also studied, demonstrating a promising PCE of 27.47%. This work unveils the role of P3CT as a passivating agent to passivate the defective sites of CsPbI2Br perovskite film surface and grain boundaries, which facilitates charge transport and reduced carrier recombination of CsPbI2Br absorber in solar cell devices.