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

Abstract

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 temperatures. A comprehensive investigation was conducted to study the effects of annealing temperatures ranging from 50 °C to 500 °C 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 TiO₂ 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 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 in the same device architecture. These findings demonstrate the potential of the ambient temperature curable TiO₂ ETL for large-area deposition and flexible PSCs.