Cross-linked polyelectrolyte reinforced SnO₂ electron transport layer for robust flexible perovskite solar cells

SnO₂ electron transport layer (ETL) is a vital component in perovskite solar cells (PSCs), due to its excellent photoelectric properties and facile fabrication process. In this study, we synthesized a water-soluble and adhesive polyelectrolyte with ethanolamine (EA) and poly-acrylic acid (PAA). The linear PAA was crosslinked by EA, forming a 3D network that stabilized the SnO₂ nanoparticle dispersion. An organic–inorganic hybrid ETL is developed by introducing the cross-linked PAA-EA into SnO₂ ETL, which prevents nano particle agglomeration and facilitates uniform SnO₂ film formation with fewer defects. Additionally, the PAA-EA-modified SnO₂ facilitated a uniform and compact perovskite film, enhancing the interface contact and carrier transport. Consequently, the PAA-EA-modified PSCs exhibited excellent PCE of 24.34% and 22.88% with high reproducibility for areas of 0.045 and 1.00 cm², respectively. Notably, owing to structure reinforce effect of PAA-EA in SnO₂ ETL, flexible device demonstrated an impressive PCE of 23.34% while maintaining 90.1% of the initial PCE after 10,000 bending cycles with a bending radius of 5 mm. This successful approach of polyelectrolyte reinforced hybrid organic–inorganic ETL displays great potential for flexible, large-area PSCs application.