Tailoring interface and morphology of TiO2 electron transport layer with potassium bitartrate for high-performance perovskite solar cells

The performance of perovskite solar cells (PSCs) has rapidly improved, largely due to advancements in mitigating inherent defects and enhancing interface carrier transport properties. Herein, we provide a facile method to improve the morphology of TiO2 ETLs, suppress defects at interface, and tailor energy level alignment to enhance carrier separation and extraction efficiency by introducing potassium bitartrate (KBT) into the TiO2 electron transport layers (ETLs), achieving high-efficiency and stable PSCs. KBT molecules can enhance the surface smoothness of TiO2 ETLs, resulting in denser and more uniform perovskite films. In addition, the carboxyl groups, hydroxyl groups, and potassium cations containing in KBT improve charge transport efficiency at TiO2/perovskite interface by reducing non-radiative recombination centers in TiO2 and perovskite bottom as well as improving energy level matching. As a result, the target PSC exhibits an obvious improvement in performance with a champion efficiency of 23.35 %, which is greatly improved relative to the control (21.66 %). The long-term operational stability is also remarkably enhanced, after 800 h MPPT, PSCs with KBT remain over 80 % of its initial efficiency. PSCs with KBT-doped ETLs exhibit increased efficiency and stability, highlighting potential of KBT as an interface engineering tool for enhancing PSCs performance