Improved Performances\nof CsPbBr<sub>3</sub> Perovskite\nSolar Cells via PbI<sub>2</sub> Additive

The emergence of CsPbBr<sub>3</sub> perovskite solar\ncells (PSCs)\nwith a band gap of approximately 2.3 eV has generated increasing interest\nstemming from their potential for high open-circuit voltage (<i>V</i><sub>oc</sub>), making them particularly suitable for use\nin tandem configurations or spectral splitting. However, the <i>V</i><sub>oc</sub> of PSCs currently falls short of its theoretical\nlimit, driven by trap-mediated charge recombination and energy band\nalignment mismatch. In this study, we present a straightforward additive\nengineering approach involving the introduction of PbI<sub>2</sub> species into the PbBr<sub>2</sub> precursor film to form the I–Pb–Br\ninteraction, retarding the rapid reaction between PbBr<sub>2</sub> and CsBr. This approach effectively suppresses the Pb-rich phase\nCsPb<sub>2</sub>Br<sub>5</sub>, eliminates pinholes on the CsPbBr<sub>3</sub> crystal, and obtains high-quality perovskite films, which\ncan significantly enhance the photovoltaic properties. Consequently,\nwe achieved CsPbBr<sub>3</sub> films characterized by enlarged crystal\nsize, complete coverage, high purity, and without pinhole presence,\nleading to a best-performed efficiency of 10.35% and a higher <i>V</i><sub>oc</sub> of up to 1.580 V compared to the power conversion\nefficiency (PCE) of 8.35% and a <i>V</i><sub>oc</sub> of\n1.442 V of the control device, along with exceptional operational\nstability.