Pre‐Buried ETL with Bottom‐Up Strategy Toward Flexible Perovskite Solar Cells with Efficiency Over 23%

Abstract With rapid development of photovoltaic technology, flexible perovskite solar cells (f‐PSCs) have attracted much attention for their light weight, high flexibility and portability. However, the power conversion efficiency (PCE) achieved so far is not yet comparable to that of rigid devices. This is mainly due to the great challenge of depositing homogeneous and high‐quality perovskite films on flexible substrate. In this study, the pre‐buried 3‐aminopropionic acid hydroiodide (3AAH) additives into the electron transport layer (ETL) and modified the ETL/perovskite (PVK) interface by a bottom‐up strategy. 3AAH treatment induced a templated perovskite grain growth and improved the quality of the ETL. By this, the residual stresses generated in PVK during the annealing‐cooling process are released and converted into micro‐compressive stresses. As a result, the defect density of f‐PSCs with pre‐buried 3AAH is reduced and the photovoltaic performance is greatly improved, reaching an exceptional PCE of 23.36%. This strategy provides a new idea to bridge the gap between flexible and rigid devices.