The Effect of Residual PbI₂ on the Performance of FAPbI₃ Perovskite Solar Cells

This study explores the influence of residual lead iodide (PbI<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>) on the performance of FAPbI<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> perovskite solar cells fabricated using a two-step close-space vapor transport process. The cells are fabricated in an n-i-p structure with the PbI<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> at the interface between the SnO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> electron contact and the FAPbI<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3.</inf> The PbI<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> content is quantified by a reaction extent parameter (y), determined from relative x-ray diffraction peak intensities. When y is within the optimal range of 0.01 to 0.1, the PbI<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> enhances solar cell performance by passivating the contact. However, excessive PbI<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> leads to low photogenerated carrier collection, while low PbI<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> levels (y < 0.01) fail to adequately passivate material imperfections. These findings highlight the critical role of precise PbI<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> control in achieving high-efficiency perovskite solar cells.