Interfacial engineering of front-contact with finely tuned polymer interlayers for high-performance large-area flexible perovskite solar cells

Inverted perovskite solar cells (PSCs) have stood out from the promising candidates for portable power source applications. Their advantageous features such as high efficiency, low cost, light weight and flexibility can be retained when a robust and compact hole transport layer (HTL) is fabricated using a low-temperature technology. To maximize the mechanical feature, the integration of graphene-derived nanomaterials is a method of choice owing to their superior physical and mechanical properties. Herein, we report an innovative method of fabricating efficient PSCs by means of inserting conjugated polyelectrolyte PTFTS interlayers between the perovskite and graphene oxide (GO) HTL. Results show that the amphiphilic polymer interlayer facilitates the growth of perovskite grains, passivates interfacial trap-states, forms better energetic alignment, and increases intermolecular interaction between PTFTS and perovskite. More importantly, strong binding force between GO and PTFTS enables uniform interlayer films obtained from a simple dip-coating method. The facile processability of the PTFTS-modified GO has been successfully extended to scalable fabrication of flexible device (1.08 cm²) with excellent device efficiency over 17.0%, the highest reported value so far for large-area flexible PSCs. This front-contact interfacial engineering offers an efficient strategy towards the widespread application of solution-processable graphene materials in practical perovskite devices.