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.