Multifunctional Polymer‐Regulated SnO2 Nanocrystals Enhance Interface Contact for Efficient and Stable Planar Perovskite Solar Cells

Abstract Perovskite solar cells (PSCs) have rapidly developed and achieved power conversion efficiencies of over 20% with diverse technical routes. Particularly, planar‐structured PSCs can be fabricated with low‐temperature (≤150 °C) solution‐based processes, which is energy efficient and compatible with flexible substrates. Here, the efficiency and stability of planar PSCs are enhanced by improving the interface contact between the SnO 2 electron‐transport layer (ETL) and the perovskite layer. A biological polymer (heparin potassium, HP) is introduced to regulate the arrangement of SnO 2 nanocrystals, and induce vertically aligned crystal growth of perovskites on top. Correspondingly, SnO 2 –HP‐based devices can demonstrate an average efficiency of 23.03% on rigid substrates with enhanced open‐circuit voltage ( V OC ) of 1.162 V and high reproducibility. Attributed to the strengthened interface binding, the devices obtain high operational stability, retaining 97% of their initial performance (power conversion efficiency, PCE > 22%) after 1000 h operation at their maximum power point under 1 sun illumination. Besides, the HP‐modified SnO 2 ETL exhibits promising potential for application in flexible and large‐area devices.