In situ Photocrosslinked Fluorinated Polyacrylate Layer for Interfacial Modification in Carbon-Based Perovskite Solar Cells

Abstract Carbon-based perovskite solar cells (C-PSCs) have attracted considerable attention owing to their low cost and excellent commercial potential. However, insufficient interfacial contact and unfavorable energy-level alignment at the perovskite/carbon interface often lead to severe nonradiative recombination and inefficient hole extraction, thus limiting device performance. Herein, two photocurable polyacrylates, poly(isopropyl acrylate) (poly(IPAc)) and fluorinated poly(1,1,1,3,3,3-hexafluoroisopropyl acrylate) (poly(HFIPAc)), are in situ polymerized as interfacial layers to investigate the molecular structure effect on the perovskite/carbon interface. A comparative study reveals that the poly(HFIPAc) layer with the electron-withdrawing effect of fluorine substituents strengthens polymer/carbon interactions. Compared with the poly(IPAc) interlayer, the as-formed poly(HFIPAc) layer exhibits better ability to enhance film crystallinity, reduce defect density, and optimize surface electronic structure and improve energy-level alignment at the interface of the perovskite and the carbon electrode. Consequently, the optimized carbon-based perovskite solar cell incorporating the poly(HFIPAc) interfacial layer achieves the champion power conversion efficiency (PCE) of 18.44%, significantly higher than that of the poly(IPAc)-treated PSCs. Meanwhile, the unencapsulated poly(HFIPAc)-treated device retains 90.5% of its initial efficiency after 1000 h of storage under ambient conditions. This work provides valuable insights on how molecular structure of polymers regulates the perovskite/carbon interface. It also provides a sustainable route toward cost-effective and stable carbon-based perovskite solar cells, taking advantage of the room-temperature UV-induced photopolymerization method and the HTL-free carbon-electrode architecture.