SnO₂ ink engineering for printing efficient flexible perovskite solar modules

Flexible perovskite solar cells have broader prospects for application over their rigid counterparts. However, they are normally prepared by the spin coating process, which is not conducive to scaling up. One of the considerable barriers to scaling up stems from the printing of electron transport layers (ETLs), with tin oxide (SnO₂) being a commonly used material. Here, poly(acrylic acid) (PAA) is introduced into the SnO₂ nanocrystals ink to engineer the ink to enhance the dispersion of nanocrystals and slow down solvent evaporation, ensuring the printed ETLs having optimized coverage and morphology. Concurrently, the buried interface is refined by PAA, which enhances charge transfer and suppresses nonradiative recombination. The flexible device modified by PAA achieves a high efficiency of 22.46% (certified at 21.56%) and retains 89.3% of its initial value after 3000 bending cycles and 92.4% after 2000 hours of storage. The printed 30 centimeter-by-30 centimeter flexible module attains an impressive efficiency of 16.40% (certified at 16.28%).