Tailoring Perovskite Adjacent Interfaces by Conjugated Polyelectrolyte for Stable and Efficient Solar Cells

Interface engineering is an effective means to enhance the performance of thin-film devices, such as perovskite solar cells (PSCs). Herein, a conjugated polyelectrolyte, poly[(9,9-bis(3 '-((N,N-dimethyl)-N-ethyl-ammonium)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)]di-iodide (PFN-I), is used at the interfaces between the hole transport layer (HTL)/perovskite and perovskite/electron transport layer simultaneously, to enhance the device power conversion efficiency (PCE) and stability. The fabricated PSCs with an inverted planar heterojunction structure show improved open-circuit voltage (V-oc), short-circuit current density (J(sc)), and fill factor, resulting in PCEs up to 20.56%. The devices maintain over 80% of their initial PCEs after 800 h of exposure to a relative humidity 35-55% at room temperature. All of these improvements are attributed to the functional PFN-I layers as they provide favorable interface contact and defect reduction.