Low-temperature curable TiO₂ sol for separator and HTM-free carbon-based perovskite solar cells

In this study, we present the development of an ambient temperature curable TiO2 mesoporous layer for perovskite solar cells (PSCs), eliminating the need for a binder and enabling the use of environmentally friendly solvents. The TiO2 layer was synthesized via a hydrothermal method followed by minimal post-processing techniques. The resulting anatase TiO2 sol was optimized to be compatible with various coating techniques such as spin coating, dip coating, and spray coating, allowing for its application at sub-50 C-degrees temperatures. A comprehensive investigation was conducted to study the effects of annealing temperatures ranging from 50 C-degrees to 500 C-degrees on the crystallographic, morphological, electrical, and surface properties of the TiO2 films derived from the TiO2 sol. Contact angle measurements were employed to analyse the change in surface energy resulting from different sintering temperatures and its influence on the growth of the perovskite film on the TiO2 films. To evaluate the performance of the TiO(2 )electron transport layers (ETLs) annealed at different temperatures, carbon-based perovskite solar cells (CPSCs) were fabricated. The results revealed that the CPSCs utilizing the TiO2 ETL annealed at 50 C-degrees exhibited the highest efficiency of 11.1%, accompanied by an open circuit voltage of 0.98 V and a current density of 22.3 mA cm(-2). Notably, the developed TiO2 ETL outperformed the commercial TiO2 ETL sintered at 500 C-degrees in the same device architecture. These findings demonstrate the potential of the ambient temperature curable TiO2 ETL for large-area deposition and flexible PSCs.