Annealing-Free SnO2 Layers for Improved Fill Factor of Perovskite Solar Cells

Perovskitesolar cells (PSCs) have developed rapidly with simplifiedplanar structures, in which the electron transport layer (ETL) isone of the key components for high efficiency. As one of the mostwidely used ETLs for PSCs, a tin dioxide (SnO2) ETL isusually obtained by thermal annealing at around 150 degrees C, whichcomplicates the fabrication process and confines the application ofPSCs onto thermally sensitive flexible substrates. Here, we adoptedan annealing-free process for the first time, the negative pressureevaporation (NPE) method, to quickly prepare SnO2 ETLs(NPE-SnO2) within 1 minute at room temperature from widelyused commercial aqueous SnO2 colloid. The NPE process developedhere significantly improves the surface morphology and conductivityof SnO2 layers compared to the traditional thermally annealedones (A-SnO2). Detailed characterizations reveal that increasedoxygen vacancies and reduced hydroxyl defects contribute to higherconductivity of NPE-SnO2 and less interfacial recombinationof PSCs. Therefore, a PSC with NPE-SnO2 delivers an improvedfill factor (FF) of 82.33% and a higher power conversion efficiency(PCE) of 23.07%, which is the highest value based on annealing-freeSnO(2). To conclude, the NPE process is a universal techniqueto obtain high-quality semiconductor films from their wet state within1 min and opens up the possibility of fabricating functional layersof PSCs without thermal annealing.