Universal buried interface modification with lead iodide for efficient and stable perovskite solar cells†

A controlled amount of excess lead iodide (PbI₂) in the perovskite precursor has been widely used in perovskite solar cells (PSCs) to enhance the device's performance by passivating defects. However, an excessive amount of PbI₂ can lead to significant hysteresis and reduced stability. Managing the excess PbI₂ in the perovskite bulk and on the top (exposed) surface is achievable, but the bottom surface presents a challenge. This study offers a method for adjusting the amount of excess PbI₂ in perovskite solar cells at both the bottom surface and the bulk of the perovskite layer. This treatment, known as buried interface modification, is effective for both negative-intrinsic-positive (n-i-p) and positive-intrinsic-negative (p-i-n) structures, achieving efficiencies of 25.9% and 24.6%, respectively, with negligible hysteresis and excellent stability of over 1000 hours under light at the maximum power point.