Incorporating polyvinyl pyrrolidone in green anti-solvent isopropanol: A facile approach to obtain high efficient and stable perovskite solar cells

Polymer additive is an effective candidate for passivating perovskite layers, which can lead to high efficiency and stability for perovskite solar cells (PSCs). Herein, we introduce a nontoxic, environment-friendly poly (4-vinylpyridine) (PVP) additives, which is beneficial in optimizing perovskite films, into the green anti-solvent isopropanol. Analysis of the photoluminescence imaging and transient spectroscopic measurements confirm the reduction in nonradiative recombination in the passivated device. The Fourier transform infrared spectroscopy and Hydrogen nuclear magnetic spectra indicate that PVP can efficiently passivate the perovskites via sharing the lone pair electrons of carbon-oxygen double bond (C=O) with uncoordinated lead ions. Furthermore, an extra hydrogen bond between PVP and CH3NH3+ (Methylammonium, MA+) can be observed by the Hydrogen Magnetic Resonance Spectroscopy. The C-O band locks MA+ through hydrogen bond which suppresses ion migration and further stabilizes the perovskite crystal structure. As a result, the power conversion efficiency of PSC increases from 15.2% to 18.2%. This work provides an environment-friendly method to introduce polymers into the fabrication of highly efficient and stable PSCs.