Inclusion of polysaccharides in perovskite thin films: from in-solution interaction to film formation and stability.

Despite perovskite solar cells (PSCs) being among the most promising photovoltaic technologies, their widespread adoption requires further advancements in material processability and long-term stability. Polysaccharides have emerged as effective additives for assisted perovskite thin film crystallization in one step dripping-free deposition. Here, with the aim of rationalising their effect, the role of the hydroxyl groups (-OH) in the polymer structure, affecting the formation of perovskite-polymer nanocomposites, has been thoroughly analysed by comparing two celluloses, hydroxyethyl cellulose (HEC) and cellulose acetate (CAT), in which some of the -OH groups are replaced by acetyl groups. The combination of nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and rheological analysis showed that HEC strongly interacts with perovskite precursors already in solution, retards DMSO evaporation and then modifies the crystallisation dynamics process, resulting in a film characterised by highly uniform grain structure and improved film stability, with a power conversion efficiency (PCE) of 15.89%. In contrast, CAT with partially substituted -OH groups showed weaker interactions resulting in non-uniform crystal growth and poor film morphology. Furthermore, Energy Dispersive X-ray Reflectivity (EDXR), Atomic Force Microscopy (AFM), and X-ray Diffraction (XRD) confirm that HEC-based films maintain structural stability under light-aging conditions, whereas pristine methylammonium lead iodide (MAPbI) undergoes significant degradation. These findings highlight the potential of HEC as an intrinsic stabilizer for perovskite films, paving the way for more durable and scalable PSC technologies.