A study on the material characteristics of low temperature cured SnO2 films for perovskite solar cells under high humidity

Electron transport layer (ETL) plays a crucial role on the fabrication of perovskite solar cells (PSCs) by separating and transporting the charge carriers. Titanium dioxide (TiO2) has been extensively used as an ETL in PSCs; however, high temperature thermal annealing requirement impedes its integration with flexible polymer substrates for roll to roll fabrication. Herein, we have demonstrated that SnO2 is a potential ETL candidate when fabricated at low temperature (180 degrees C) using spin coating technique. XRD and XPS analysis revealed synthesis of rutile SnO2 tetragonal phase. TEM micrographs with SAED pattern proved formation of nanosized (3 to 4 nm) crystals of SnO2 with polycrystalline phase. FESEM analysis revealed the SnO2 nanocrystals fully covered the FTO surface and elemental mapping confirmed the uniformly distribution tin (Sn) and (O) elements throughout the surface. In addition to this, transmission analysis confirmed that SnO2 film exhibited good transmission property. PSCs were fabricated in ambient air (relative humidity ranges from 55% to 65%) with concentrated SnO2 colloidal solution and diluted SnO2 with different concentrations (1:1 v/v, 1:2 v/v, 1:4 v/v and 1:6 v/v). It was found that 1:4 v/v based diluted colloidal solution of SnO2 in DI water film exhibited the highest PSC performance of 8.51% in ambient conditions. Thus, low temperature solution processed SnO2 is an efficient ETL and well-suited for low cost automated fabrication of PSCs at large scale.